ORCID Profile
0000-0002-1345-3821
Current Organisations
F. Hoffmann-La Roche Ltd
,
University of Basel
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Nanomaterials | Central Nervous System | Biomechanics | Psychology | Learning, Memory, Cognition And Language | Medical Devices | Human Movement and Sports Science | Sensory Processes, Perception And Performance | Nanotechnology | Sensor Technology (Chemical aspects) | Biomedical Engineering | Biomechanical Engineering | Radiology And Organ Imaging |
Diagnostic Methods | Mental health | Nervous system and disorders | Health related to ageing | Health Status (e.g. Indicators of Well-Being) | Medical instrumentation | Biological sciences | Diagnostic methods
Publisher: Public Library of Science (PLoS)
Date: 17-10-2007
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 03-2007
DOI: 10.1016/J.PAIN.2006.08.013
Abstract: The insula is involved in processing noxious information. It is consistently activated by acute noxious stimuli, can elicit pain on stimulation, and lesions encompassing the insula can alter pain perception. Anatomical tracing, electrophysiological and functional brain imaging investigations have suggested that the insula is somatotopically organized with respect to noxious cutaneous inputs. It has also recently been revealed that the anterior insula displays differential activation during cutaneous compared with muscle pain. Given this difference, it is important to determine if an insula somatotopy also exists for muscle pain. Using high-resolution functional magnetic resonance imaging (fMRI) we compared insula activation patterns in 23 subjects during muscle and cutaneous pain induced in the right leg and forearm. Group and frequency analyses revealed somatotopically organized signal increases in the posterior contralateral (left) and ipsilateral (right) anterior insula. Within the posterior contralateral insula, signal increases during both cutaneous and muscle forearm pain were located lateral and anterior to those evoked by leg pain, whereas in the ipsilateral anterior insula the pattern was reversed. Furthermore, within the ipsilateral anterior insula, muscle pain activated a region anterior to that activated by cutaneous pain. This somatotopic organization may be crucial for pain localization or other aspects of the pain experience that differ depending on both stimulation site and type of tissue activated. This study reveals that the insula is organized somatopically with respect to muscle and cutaneous pain and that this organization is further separated according to the tissue in which the pain originates.
Publisher: American Physiological Society
Date: 05-2017
DOI: 10.1152/JAPPLPHYSIOL.00775.2016
Abstract: Sustained physical exercise leads to a reduced capacity to produce voluntary force that typically outlasts the exercise bout. This “fatigue” can be due both to impaired muscle function, termed “peripheral fatigue,” and a reduction in the capacity of the central nervous system to activate muscles, termed “central fatigue.” In this review we consider the factors that determine the recovery of voluntary force generating capacity after various types of exercise. After brief, high-intensity exercise there is typically a rapid restitution of force that is due to recovery of central fatigue (typically within 2 min) and aspects of peripheral fatigue associated with excitation-contraction coupling and reperfusion of muscles (typically within 3–5 min). Complete recovery of muscle function may be incomplete for some hours, however, due to prolonged impairment in intracellular Ca 2+ release or sensitivity. After low-intensity exercise of long duration, voluntary force typically shows rapid, partial, recovery within the first few minutes, due largely to recovery of the central, neural component. However, the ability to voluntarily activate muscles may not recover completely within 30 min after exercise. Recovery of peripheral fatigue contributes comparatively little to the fast initial force restitution and is typically incomplete for at least 20–30 min. Work remains to identify what factors underlie the prolonged central fatigue that usually accompanies long-duration single joint and locomotor exercise and to document how the time course of neuromuscular recovery is affected by exercise intensity and duration in locomotor exercise. Such information could be useful to enhance rehabilitation and sports performance.
Publisher: Wiley
Date: 31-08-2016
DOI: 10.1113/EP085907
Publisher: Oxford University Press (OUP)
Date: 08-02-2006
Publisher: American Physiological Society
Date: 09-2016
DOI: 10.1152/JAPPLPHYSIOL.00293.2016
Abstract: This article reviews the use of transcranial magnetic stimulation (TMS) over the motor cortex to make estimates of the level of voluntary drive to muscles. The method, described in 2003 (Todd et al. J Physiol 551: 661-671, 2003), uses a TMS pulse to produce descending corticospinal volleys that synaptically activate motoneurons, resulting in a muscle twitch. Linear regression of the superimposed twitch litude and voluntary force (or torque) can generate an “estimated” resting twitch for muscles involved in a task. This procedure has most commonly been applied to elbow flexors but also to knee extensors and other muscle groups. Data from 44 papers using the method were tabulated. We identify and discuss five major technical challenges, and the frequency with which they are addressed. The technical challenges include inadvertent activation of the cortical representation of antagonist muscles, the role of antagonist torques at the studied joint, uncertainty about the effectiveness of the TMS pulse in activating the motoneuron pool, the linearity of the voluntary force (or torque) and superimposed twitch relationship, and variability in the TMS-evoked EMG and force/torque responses. The ideal situation in which the descending corticospinal volleys recruit all of the agonist motoneurons and none of the antagonist motoneurons is unlikely to ever occur, and hence results must be carefully examined to assess the authenticity of the voluntary activation estimates in the context of the experimental design. A partial compromise lies in the choice of stimulus intensity. We also identify aspects of the procedure that require further investigation.
Publisher: American Physiological Society
Date: 09-2021
DOI: 10.1152/JAPPLPHYSIOL.00078.2021
Abstract: Upper limb motor impairment is a common manifestation after stroke, compromising independence in fundamental daily activities involving the ability to reach, grasp, and manipulate objects. The upper limb Physiological Profile Assessment (PPA) offers a means of quantifying performance of the in idual sensorimotor domains that are essential for upper limb function. Establishing in idual performance profiles based on age- and sex-based normative scores may facilitate in idualized treatment decisions by identifying the stroke patient’s specific strengths and limitations.
Publisher: American Physiological Society
Date: 02-2014
Publisher: American Physiological Society
Date: 11-2022
DOI: 10.1152/JAPPLPHYSIOL.00064.2022
Abstract: Sensations of breathing are thought to be impaired following chronic tetraplegia. The detection threshold for an added resistive load during inspiration was higher in people with tetraplegia than in healthy able-bodied participants. However, for inspiratory loads above the detection threshold, the perceived magnitude of a resistive load as a function of the peak inspiratory pressure was greater in tetraplegia. Load magnitude perception was comparable between participant groups when peak pressure was ided by maximal inspiratory pressure.
Publisher: Springer Science and Business Media LLC
Date: 26-01-2011
DOI: 10.1007/S00221-011-2552-Z
Abstract: When two motor cortical stimuli are delivered with an interstimulus interval of 50-200 ms, the response (motor evoked potential MEP) to the second stimulus is typically suppressed. This phenomenon is termed long-interval intracortical inhibition (LICI), although data from one subject suggest that facilitation is possible. Moreover, we recently showed that suppression can be mediated at a spinal level. We characterized LICI more fully by exploring a broad range of contraction strengths and test stimulus intensities. MEPs were evoked in first dorsal interosseous by transcranial magnetic stimulation over the motor cortex. Single test and paired (conditioning-test interval of 100 ms) stimuli at intensities of 100-160% resting motor threshold were delivered at rest or during brief contractions of 10, 25, or 100% maximal voluntary force. Inhibition or facilitation was quantified with the standard ratio in which conditioned MEPs were expressed as a percentage of unconditioned MEPs. Inhibition was greatest at weak-moderate contraction strengths and least at rest and during maximal efforts. Both at rest and during maximal efforts, MEPs evoked by strong stimuli were facilitated. In a subset of subjects, cervicomedullary stimulation was used to activate the corticospinal tract to identify possible spinal influences on changes to MEPs. Contraction strength and test stimulus intensity each had different effects on unconditioned and conditioned MEP size, and hence, LICI is highly dependent on both factors. Further, because motoneurons are facilitated during contraction but disfacilitated after a strong conditioning stimulus, the standard ratio of LICI is of questionable validity during voluntary contractions.
Publisher: American Physiological Society
Date: 03-2020
DOI: 10.1152/JAPPLPHYSIOL.00831.2019
Abstract: A premotor potential, or Bereitschaftspotential (BP), is a low- litude negativity in the electroencephalographic activity (EEG) of the sensorimotor cortex. It begins ~1 s prior to the onset of inspiration in the averaged EEG. Although normally absent during quiet breathing in healthy, younger people, inspiration-related BPs are present in people with respiratory disease and healthy, older people, indicating a cortical contribution to quiet breathing. People with tetraplegia have weak respiratory muscles and increased neural drive during quiet breathing, indicated by increased inspiratory muscle activity. Therefore, we hypothesized that BPs would be present during quiet breathing in people with tetraplegia. EEG was recorded in 17 people with chronic tetraplegia (14M, 3 female 22–51 yr C3–C7, American Spinal Injury Association Impairment Scale A–D yr postinjury). They had reduced lung function and respiratory muscle weakness [FEV 1 : 54 ± 19% predicted, FVC: 59 ± 22% predicted and MIP: 56 ± 24% predicted (mean ± SD)]. Participants performed quiet breathing and voluntary self-paced sniffs (positive control condition). A minimum of 250 EEG epochs during quiet breathing and 60 epochs during sniffs, time-locked to the onset of inspiration, were averaged to determine the presence of BPs at Cz, FCz, C3, and C4. Fifteen participants (88%) had a BP for the sniffs. Of these 15 participants, only one (7%) had a BP in quiet breathing, a rate similar to that reported during quiet breathing in young able-bodied participants (12%). The findings suggest that, as in young able-bodied people, a cortical contribution to quiet breathing is absent in people with tetraplegia despite higher neural drive. NEW & NOTEWORTHY People with tetraplegia have weak respiratory muscles, increased neural drive during quiet breathing, and a high incidence of sleep-disordered breathing. Using electroencephalographic recordings, we show that inspiratory premotor potentials are absent in people with chronic tetraplegia during quiet breathing. This suggests that cortical activity is not present during resting ventilation in people with tetraplegia who are awake and breathing independently.
Publisher: Wiley
Date: 13-10-2017
DOI: 10.1113/JP274866
Publisher: American Physiological Society
Date: 02-2022
DOI: 10.1152/JAPPLPHYSIOL.00478.2021
Abstract: During swallowing, we observed two distinct, stereotyped muscle activation patterns that define the horizontal (monophasic, maximal EMG) and oblique (biphasic, submaximal EMG) neuromuscular compartments of genioglossus. In contrast, volitional tongue protrusions produced uniform activation across compartments. This provides evidence for task-dependent, functionally discrete neuromuscular control of the oblique and horizontal compartments of genioglossus. The magnitude and temporal patterning of genioglossus EMG during swallowing may help guide electrode placement in tongue EMG studies.
Publisher: Wiley
Date: 07-12-2015
DOI: 10.1113/JP271108
Publisher: Wiley
Date: 30-11-2009
Publisher: Wiley
Date: 14-03-2011
DOI: 10.1002/MUS.21938
Abstract: After maximal voluntary contractions (MVCs), responses to corticospinal tract stimulation change differently in arm and leg muscles. This study we examined responses in the first dorsal interosseous muscle (FDI). Stimulation of the corticospinal tract at the cervicomedullary motor evoked potentials in FDI. Stimuli were delivered before and after 10-s and 1-min MVCs. The reproducibility of changes in the cervicomedullary motor evoked potentials (CMEPs) was investigated. F-waves tested motoneuron excitability. After the MVCs, the CMEP area was initially variable. By ~1 min after 10-s and 1-min MVCs, CMEPs in relaxed muscle decreased to 63 ± 15% and 52 ± 32%, respectively, of control and remained depressed for ~10 min. Responses evoked 2 days apart varied between subjects but not between days. After 10-s MVCs, F-waves were reduced at rest. During weak contraction, CMEPs but not F-waves were depressed. Our results suggest that contraction produces changes at the corticomotoneuronal synapses to FDI. In addition, motoneuron excitability is reduced.
Publisher: Wiley
Date: 28-03-2017
DOI: 10.1111/PSYP.12865
Abstract: Up to a third of the population experiences pain when seeing another in pain. The mechanisms underlying such vicarious sensory experiences are thought to reflect hyperactive mirror systems (threshold theory) or dysfunctional processing and representation of oneself versus others (self/other theory). This study investigated whether the tendency to experience vicarious pain corresponds to disinhibited physiological reactivity toward other's emotions, and/or greater empathic mimicry of other's physiological state (respiratory behavior) during fear, pain, and positive emotion. Fifty healthy in iduals aged 18-55 years (23 vicarious pain responders) completed empathy- and anxiety-related questionnaires, and a film task. Respiration was measured noninvasively with piezoelectric respiration belts while participants viewed emotional film clips depicting three emotions (fear ain ositive) interspersed with neutral clips. The emotional stimuli depicted scenes in which the characters showed increases or decreases in respiration. The results suggest that vicarious pain responders do not mimic emotional respiratory behavior. Rather, vicarious pain responders had a significantly slower respiration rate for all emotional stimuli (M
Publisher: Oxford University Press (OUP)
Date: 03-2013
DOI: 10.5665/SLEEP.2458
Abstract: To characterize tongue and lateral upper airway movement and to image tongue deformation during mandibular advancement. Dynamic imaging study of a wide range of apnea hypopnea index (AHI), body mass index (BMI) subjects. Not-for-profit research institute. 30 subjects (aged 31-69 y, AHI 0-75 events/h, BMI 17-39 kg/m2). Subjects were imaged using dynamic tagged magnetic resonance imaging during mandibular advancement. Tissue displacements were quantified with the harmonic phase technique. Mean mandibular advancement was 5.6 ± 1.8 mm (mean ± standard deviation). This produced movement through a connection from the ramus of the mandible to the pharyngeal lateral walls in all subjects. In the sagittal plane, 3 patterns of posterior tongue deformation were seen with mandibular advancement—(A) en bloc anterior movement, (B) anterior movement of the oropharyngeal region, and (C) minimal anterior movement. Subjects with lower AHI were more likely to have en bloc movement (P = 0.04) than minimal movement. Antero-posterior elongation of the tongue increased with AHI (R = 0.461, P = 0.01). Mean anterior displacements of the posterior nasopharyngeal and oropharyngeal regions of the tongue were 20% ± 13% and 31% ± 17% of mandibular advancement. The posterior tongue compressed 1.1 ± 2.2 mm supero-inferiorly. Mandibular advancement has two mechanisms of action which increase airway size. In subjects with low AHI, the entire tongue moves forward. Mandibular advancement also produces lateral airway expansion via a direct connection between the lateral walls and the ramus of the mandible.
Publisher: American Physiological Society
Date: 03-2009
DOI: 10.1152/JAPPLPHYSIOL.91365.2008
Abstract: Joint position sense is believed to be mediated by muscle afferent signals. Because a “phantom” hand produced by a sensory and motor nerve block appears to move in the direction of voluntary effort, signals of “motor command” or “effort” can influence perceived joint position. To determine whether this occurs when sensory signals are available, three studies assessed position sense when motor command and afferent signals were available, but joint movement was prevented. First, the hand was positioned to stop movement at the proximal joint of the middle finger, and movement at the distal joint was impossible because the muscles had been “disengaged”. Voluntary efforts produced illusory position changes in the direction of the effort (12.6 ± 2.0° distal joint 12.3 ± 2.3° proximal joint for efforts at 30% maximum means ± SD). Second, when subjects attempted to move the index finger under isometric conditions, the index finger appeared to move 7.4 ± 1.2° in the direction of efforts. These illusions graded with the level of effort (10 or 30% maximum) and far exceeded any real joint movement. Finally, because changes in muscle afferent feedback might have accompanied the voluntary efforts, all forearm and hand muscles were completely paralyzed by locally infused rocuronium. During paralysis, passive wrist position was signaled accurately, but, during attempted efforts (30% maximum), perceived wrist position changed by 9.7 ± 4.9°. Before paralysis, isometric efforts changed it by 6.7 ± 3.6°. Thus all studies concur: when joint movement is prevented, signals of motor command contribute to joint position sense.
Publisher: Springer Science and Business Media LLC
Date: 09-07-2015
Publisher: Wiley
Date: 05-10-2012
DOI: 10.1002/MUS.23438
Abstract: Costal diaphragm electromyography (EMG) remains unpopular due to the risk of pneumothorax. In this study we assessed the safety of the "trans-intercostal" method of diaphragm EMG using B-mode ultrasound. Twenty healthy subjects participated in this investigation. The diaphragm and the lung were visualized in the most distal intercostal space (dICS) with ultrasound. The risk of pneumothorax was assessed at the mid-clavicular, anterior, and mid-axillary levels, during normal and deep breathing, in supine and upright postures. The dICS at the anterior axillary level was the safest landmark for diaphragm EMG during normal breathing, with the subject supine. The mid-clavicular level is the least optimal location for EMG. The upright position and deep breaths increase the risk of pneumothorax. The safety of the trans-intercostal method of diaphragm EMG depends on the anatomic level chosen to insert the needle, patient position, and breathing pattern. Hence, we have developed a safety algorithm for electromyographers.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 07-2013
Publisher: Elsevier BV
Date: 02-2008
DOI: 10.1016/J.NEUROIMAGE.2007.10.045
Abstract: Gender greatly influences pain processing. Not only do females display greater pain sensitivity, many chronic pain conditions affect females more than males. Although gender-based differences in pain sensitivity may be related to cultural and social factors, animal studies also reveal gender differences in pain sensitivity, suggesting that physiological factors may contribute to differences in the processing of pain in males and females. It has been recently reported that noxious cutaneous heat stimuli evoke gender-based differences in activity in some brain regions. Given that most chronic pain conditions, including those with gender bias are of "deep" origin (e.g. arising in muscle, joints or viscera), we investigated whether gender differences also exist in the central processing of muscle pain. In 24 healthy adults we used functional magnetic resonance imaging (fMRI) to measure signal intensity changes during muscle and cutaneous pain induced by intramuscular and subcutaneous injections of hypertonic saline, respectively. In addition to activating the "pain neuromatrix", i.e. cingulate, insular, somatosensory and cerebellar cortices, both muscle pain and cutaneous pain evoked gender-based differences in the mid-cingulate cortex, dorsolateral prefrontal cortex, hippoc us and cerebellar cortex. These differences may reflect differences in emotional processing of noxious information in men and women and may underlie the gender bias that exists in many chronic pain conditions.
Publisher: Wiley
Date: 13-02-2009
Publisher: American Physiological Society
Date: 05-2020
DOI: 10.1152/JAPPLPHYSIOL.00790.2019
Abstract: Simultaneous electromyographic recordings from the human costal and crural diaphragm during voluntary augmented breathing and involuntary rebreathing show that the increase in inspiratory crural diaphragm activity was ~60% of the increase in costal diaphragm activity. However costal to crural diaphragm activation did not differ between the two tasks. The dissociation in the litude of activation of the costal and crural diaphragm becomes apparent only as the drive to breathe increases above tidal breathing.
Publisher: Elsevier BV
Date: 06-1989
DOI: 10.1016/0013-4694(89)90229-0
Abstract: Somatosensory evoked potentials to electrical stimulation of muscle and cutaneous afferents from the foot were recorded in normal human subjects using multiple channels centred on the vertex and referenced to the contralateral earlobe. Low-threshold muscle afferents were selectively activated by an insulated microelectrode inserted percutaneously at the motor point of abductor hallucis. Low-threshold cutaneous and joint afferents of the hallux or second toe were stimulated with ring electrodes. The posterior tibial and sural nerves were stimulated at the ankle through surface electrodes. The cerebral distribution of the initial cortical response (N33-P40) to stimulation of muscle afferents largely paralleled that to stimulation of its parent nerve, the posterior tibial nerve (which contains afferents of muscle, cutaneous and joint origin). They were maximal slightly posterior and ipsilateral to the vertex. The cutaneous-joint afferent projection from the hallux paralleled that from the sural nerve and both were less lateralized than the tibial and abductor hallucis projections.
Publisher: American Physiological Society
Date: 02-2016
Abstract: Motoneurons often fire repetitively and for long periods. In sustained voluntary contractions the excitability of motoneurons declines. We provide the first detailed description of the time course of human motoneuron recovery after sustained activity at a constant discharge rate. We recorded the discharge of single motor units (MUs, n = 30) with intramuscular wire electrodes inserted in triceps brachii during weak isometric contractions. Subjects ( n = 15) discharged single MUs at a constant frequency (∼10 Hz) with visual feedback for prolonged durations (3–7 min) until rectified surface electromyogram (sEMG) of triceps brachii increased by ∼100%. After a rest of 1–2, 15, 30, 60, 120, or 240 s, subjects briefly resumed the contraction with the target MU at the same discharge rate. Each MU was tested with three to four rest periods. The magnitude of sEMG was increased when contractions were resumed, and the target motoneuron discharged at the test frequency following rest intervals of 2–60 s ( P = 0.001–0.038). The increased sEMG indicates that greater excitatory drive was needed to discharge the motoneuron at the test rate. The increase in EMG recovered exponentially with a time constant of 28 s but did not return to baseline even after a rest period of ∼240 s. Thus the decline in motoneuron excitability from a weak contraction takes several minutes to recover fully.
Publisher: Wiley
Date: 12-2002
DOI: 10.1113/JPHYSIOL.2002.032854
Abstract: Voluntary contractions induce thixotropic changes in intrafusal muscle fibres and hence, by induction or removal of "slack", the background discharge and sensitivity of spindle endings to stretch is altered. This study assessed whether such changes also altered the "excitability" of the motor cortex. Eleven subjects performed a series of voluntary conditioning contractions of the wrist flexors designed to remove slack in the intrafusal fibres (contract and test at intermediate length, termed "contract-test") or to introduce slack (contract at long length and test at intermediate length, termed "contract-long"). Surface electromyographic recordings were made from one wrist flexor, flexor carpi radialis. Subjects relaxed after each contraction, and 10 s later a test stimulus was applied to elicit a tendon tap response, H-reflex, or motor-evoked potential (MEP) to transcranial magnetic stimulation in the flexor carpi radialis. Each of the three test stimuli was applied during 15 consecutive pairs of contractions ("contract-long" and "contract-test"). Three subjects repeated the protocol using transmastoid electrical stimulation as the test stimulus to evoke a cervicomedullary motor-evoked potential (CMEP). For the group of subjects, after conditioning contractions designed to induce slack there was a significant reduction in the litude of the tendon reflex, no significant change in the H-reflex, and a small but significant reduction in the litude of the MEP. In one subject the CMEP was significantly reduced, while it was unchanged in two others. In the absence of corresponding changes in the H-reflex (or CMEP), changes in the size of the response to motor cortical stimulation suggest that the level of motor cortical "excitability" changes according to naturally induced variations in the discharge of muscle spindle afferents.
Publisher: Frontiers Media SA
Date: 2013
Publisher: American Physiological Society
Date: 07-2009
DOI: 10.1152/JAPPLPHYSIOL.91635.2008
Abstract: Neuromuscular electrical stimulation (NMES) generates contractions by activation of motor axons (peripheral mechanism), but the afferent volley also contributes by recruiting spinal motoneurons synaptically (central mechanism), which recruits motoneurons according to Henneman's size principle. Thus, we hypothesized that contractions that develop due to a combination of peripheral and central mechanisms will fatigue less rapidly than when electrically evoked contractions are generated by the activation of motor axons alone. Plantar-flexion torque evoked by NMES over the triceps surae was compared in five able-bodied subjects before (Intact) and during (Blocked) a complete anesthetic block of the tibial and common peroneal nerves. In the Blocked condition, plantar-flexion torque could only develop from the direct activation of motor axons beneath the stimulating electrodes. NMES was delivered using three protocols: protocol A, constant 100 Hz for 30 s protocol B, four 2-s bursts of 100 Hz alternating with 20-Hz stimulation and protocol C, alternating 100 Hz bursts (1 s on, 1 s off) for 30 s. The percent change in evoked plantar flexion torque from the beginning to the end of the stimulation differed ( P 0.05) between Intact and Blocked conditions for all protocols (Intact: protocol A = +125%, B = +230%, C = +78% Blocked: protocol A = −79%, B = −15%, C = −35%). These results corroborate previous evidence that NMES can evoke contractions via the recruitment of spinal motoneurons in addition to the direct recruitment of motor axons. We now show that NMES delivered for periods of up to 30 s generates plantar-flexion torque which decreases when only motor axons are recruited and increases when the central nervous system can contribute.
Publisher: Wiley
Date: 05-03-2018
DOI: 10.1113/JP275816
Publisher: Springer Science and Business Media LLC
Date: 11-1992
DOI: 10.1007/BF00227850
Publisher: American Physiological Society
Date: 15-08-2012
DOI: 10.1152/JAPPLPHYSIOL.00111.2012
Abstract: The plantarflexors of the lower limb are often assumed to act as independent actuators, but the validity of this assumption is the subject of considerable debate. This study aims to determine the degree to which passive changes in gastrocnemius muscle length, induced by knee motion, affect the tension in the adjacent soleus muscle. A second aim is to quantify the magnitude of myofascial passive force transmission between gastrocnemius and adjacent soleus. Fifteen healthy volunteers participated. Simultaneous ultrasound images of the gastrocnemius and soleus muscles were obtained during passive knee flexion (0–90°), while keeping the ankle angle fixed at either 70° or 115°. Image correlation analysis was used to quantify muscle fascicle lengths in both muscles. The data show that the soleus muscle fascicles elongate significantly during gastrocnemius shortening. The approximate change in passive soleus force as a result of the observed change in fascicle length was estimated and appears to be N, but this estimate is sensitive to the assumed slack length of soleus.
Publisher: American Physiological Society
Date: 02-2010
Publisher: American Thoracic Society
Date: 07-2008
Publisher: Oxford University Press (OUP)
Date: 1992
Abstract: In contrast to the cortical connections to and from the muscles of the hand, the transmission of an afferent volley from the intercostal muscles to the cerebral cortex takes approximately 10 ms longer than it takes a cortical motor volley to reach the muscle. This disparity in afferent and efferent cortical transmission times could be due to a slower peripheral conduction velocity of intercostal muscle afferents or a slower afferent conduction within the central nervous system. The present study derived peripheral and central conduction times for the truncal muscles from the onsets of the mechanically evoked intercostal and abdominal spinal reflexes and the onsets of the cortical sensory potentials. Mean latencies of the ipsilateral intercostal and abdominal reflexes (evoked and recorded in the mid-clavicular line) were 11.9 +/- 0.7 (SEM) ms and 13.7 +/- 0.9 ms, respectively calculated peripheral conduction velocities were 69.4 +/- 4.1 m/s and 56.2 +/- 2.3 m/s (assuming equal velocities for the sensory and motor axons and an intraspinal delay of 1 ms). Central sensory conduction time (spinal cord to cortex) was calculated by subtracting the peripheral conduction times for the intercostal and abdominal afferents (5.5 +/- 0.3 ms and 6.4 +/- 0.4 ms) from the onsets of the cortical sensory potentials (19.4 +/- 0.8 ms and 25.3 +/- 12.3 ms) central sensory conduction times (14.2 +/- 1.7 ms and 18.6 +/- 2.3 ms) were 8-11 ms longer than central motor conduction times. These results demonstrate that peripheral conduction velocities of intercostal and abdominal afferents are not slow, and that, when compared with the extremities, there is a relatively long central conduction time for proprioceptive information from the trunk to the cerebral cortex.
Publisher: Elsevier BV
Date: 03-2014
DOI: 10.1016/J.APMR.2013.09.017
Abstract: To determine whether impaired performance in a range of vision, proprioception, neuropsychological, balance, and mobility tests and pain and fatigue are associated with falls in people with multiple sclerosis (PwMS). Prospective cohort study with 6-month follow-up. A multiple sclerosis (MS) physiotherapy clinic. Community-dwelling people (N=210 age range, 21-74y) with MS (Disease Steps 0-5). Not applicable. Incidence of falls during 6 months' follow-up. In the 6-month follow-up period, 83 participants (39.7%) experienced no falls, 57 (27.3%) fell once or twice, and 69 (33.0%) fell 3 or more times. Frequent falling (≥3) was associated with increased postural sway (eyes open and closed), poor leaning balance (as assessed with the coordinated stability task), slow choice stepping reaction time, reduced walking speed, reduced executive functioning (as assessed with the difference between Trail Making Test Part B and Trail Making Test Part A), reduced fine motor control (performance on the 9-Hole Peg Test [9-HPT]), and reported leg pain. Increased sway with the eyes closed, poor coordinated stability, and reduced performance in the 9-HPT were identified as variables that significantly and independently discriminated between frequent fallers and nonfrequent fallers (model χ(2)3=30.1, P<.001). The area under the receiver operating characteristic curve for this model was .712 (95% confidence interval, .638-.785). The study reveals important balance, coordination, and cognitive determinants of falls in PwMS. These should assist the development of effective strategies for prevention of falls in this high-risk group.
Publisher: American Physiological Society
Date: 03-2010
Abstract: The parasternal intercostal muscles are obligatory inspiratory muscles. To test the hypothesis that they are also involved in trunk rotation and to assess the effect of any postural role on inspiratory drive to the muscles, intramuscular electromyographic (EMG) recordings were made from the parasternal intercostals on the right side in six healthy subjects during resting breathing in a neutral posture (“neutral breaths”), during an isometric axial rotation effort of the trunk to the right (“ipsilateral rotation”) or left (“contralateral rotation”), and during resting breathing with the trunk rotated. The parasternal intercostals were commonly active during ipsilateral rotation but were consistently silent during contralateral rotation. In addition, with ipsilateral rotation, peak parasternal inspiratory activity was 201 ± 19% (mean ± SE) of the peak inspiratory activity in neutral breaths ( P 0.001), and activity commenced earlier relative to the onset of inspiratory flow. These changes resulted from an increase in the discharge frequency of motor units (14.3 ± 0.3 vs. 11.0 ± 0.3 Hz P 0.001) and the recruitment of new motor units. The majority of units that discharged during ipsilateral rotation were also active in inspiration. However, with contralateral rotation, parasternal inspiratory activity was delayed relative to the onset of inspiratory flow, and peak activity was reduced to 72 ± 4% of that in neutral breaths ( P 0.001). This decrease resulted from a decrease in the inspiratory discharge frequency of units (10.5 ± 0.2 vs. 12.0 ± 0.2 Hz P 0.001) and the derecruitment of units. These observations confirm that in addition to an inspiratory function, the parasternal intercostal muscles have a postural function. Furthermore the postural and inspiratory drives depolarize the same motoneurons, and the postural contraction of the muscles alters their output during inspiration in a direction-dependent manner.
Publisher: Wiley
Date: 16-01-2020
DOI: 10.1113/JP278769
Publisher: American Physiological Society
Date: 08-2009
DOI: 10.1152/JAPPLPHYSIOL.00163.2009
Abstract: Inspiratory muscles are uniquely adapted for endurance, but their function is compromised in chronic obstructive pulmonary disease (COPD) due to increased loads, reduced mechanical advantage, and increased ventilatory requirements. The hyperinflation of COPD reduces the flow and pressure-generating capacity of the diaphragm. This is compensated by a threefold increase in neural drive, adaptations of the chest wall and diaphragm shape to accommodate the increased volume, and adaptations of muscle fibers to preserve strength and increase endurance. Paradoxical indrawing of the lower costal margin during inspiration in severe COPD (Hoover's sign) correlates with high inspiratory drive and severe airflow obstruction rather than contraction of radially oriented diaphragm fibers. The inspiratory muscles remain highly resistant to fatigue in patients with COPD, and the ultimate development of ventilatory failure is associated with insufficient central drive. Sleep is associated with reduced respiratory drive and impairments of lung and chest wall function, which are exaggerated in COPD patients. Profound hypoxemia and hypercapnia can occur in rapid eye movement sleep and contribute to the development of cor pulmonale. Inspiratory muscles adapt to chronic loading with an increased proportion of slow, fatigue-resistant fiber types, increased oxidative capacity, and reduced fiber cross-sectional area, but the capacity of the diaphragm to increase ventilation in exercise is compromised in COPD. In COPD, neural drive to the diaphragm increases to near maximal levels in exercise, but it does not develop peripheral muscle fatigue. The improvement in exercise capacity and dyspnea following lung volume reduction surgery is associated with a substantial reduction in neural drive to the inspiratory muscles.
Publisher: American Physiological Society
Date: 09-2022
DOI: 10.1152/JAPPLPHYSIOL.00083.2021
Abstract: Our findings indicate that 30% of participants had regional heterogeneity in reflex morphology (excitation/inhibition) to brief pulses of negative upper-airway pressure across anterior oblique, anterior horizontal, posterior oblique, and posterior horizontal regions of the genioglossus muscle. Reflex excitation litude was proportional to prestimulus drive, with increased activation in oblique compared with horizontal regions of the posterior tongue. People with narrower upper-airway anatomy tended to have increased genioglossus reflex litude to negative pressure pulses during wakefulness.
Publisher: Springer Science and Business Media LLC
Date: 06-12-2017
DOI: 10.1038/SC.2016.162
Abstract: Within-participant randomised controlled trial. To determine whether strength training combined with usual care increases strength in partially paralysed muscles of people with recent spinal cord injury (SCI) more than usual care alone. SCI units in Australia and India. Thirty people with recent SCI undergoing inpatient rehabilitation participated in this 12-week trial. One of the following muscle groups was selected as the target muscle group for each participant: the elbow flexors, elbow extensors, knee flexors or knee extensors. The target muscle on one side of the body was randomly allocated to the experimental group and the same muscle on the other side of the body was allocated to the control group. Strength training was administered to the experimental muscle but not to the control muscle. Participants were assessed at baseline and 12 weeks later. The primary outcome was maximal isometric muscle strength, and the secondary outcomes were spasticity, fatigue and participants' perception of function and strength. There were no dropouts, and participants received 98% of the training sessions. The mean (95% confidence interval (CI)) between-group difference for isometric strength was 4.3 Nm (1.9-6.8) with a clinically meaningful treatment effect of 2.7 Nm. The mean (95% CI) between-group difference for spasticity was 0.03/5 points (-0.25 to 0.32). Strength training increases strength in partially paralysed muscles of people with recent SCI, although it is not clear whether the size of the treatment effect is clinically meaningful. Strength training has no deleterious effects on spasticity.
Publisher: Wiley
Date: 07-2016
DOI: 10.1113/JP272663
Publisher: Wiley
Date: 11-04-2003
DOI: 10.1002/MUS.10375
Abstract: To investigate the ability of ultrasonography to estimate muscle activity, we measured architectural parameters (pennation angles, fascicle lengths, and muscle thickness) of several human muscles (tibialis anterior, biceps brachii, brachialis, transversus abdominis, obliquus internus abdominis, and obliquus externus abdominis) during isometric contractions of from 0 to 100% maximal voluntary contraction (MVC). Concurrently, electromyographic (EMG) activity was measured with surface (tibialis anterior only) or fine-wire electrodes. Most architectural parameters changed markedly with contractions up to 30% MVC but changed little at higher levels of contraction. Thus, ultrasound imaging can be used to detect low levels of muscle activity but cannot discriminate between moderate and strong contractions. Ultrasound measures could reliably detect changes in EMG of as little as 4% MVC (biceps muscle thickness), 5% MVC (brachialis muscle thickness), or 9% MVC (tibialis anterior pennation angle). They were generally less sensitive to changes in abdominal muscle activity, but it was possible to reliably detect contractions of 12% MVC in transversus abdominis (muscle length) and 22% MVC in obliquus internus (muscle thickness). Obliquus externus abdominis thickness did not change consistently with muscle contraction, so ultrasound measures of thickness cannot be used to detect activity of this muscle. Ultrasound imaging can thus provide a noninvasive method of detecting isometric muscle contractions of certain in idual muscles.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 09-2005
DOI: 10.1249/01.MSS.0000177583.41245.F8
Abstract: To compare effects on strength in the early phase of resistance training with one or three sets and fast or slow speeds. A total of 115 healthy, untrained subjects were randomized to a control group or one of four training groups: one set fast (approximately 140 degrees.s(-1)), three sets fast, one set slow (approximately 50 degrees.s(-1)), or three sets slow. All subjects attended training 3 x wk(-1) for 6 wk. Subjects in the training groups performed unilateral elbow flexion contractions with a target six- to eight-repetition maximum load. Control subjects sat at the training bench but did not train. One repetition maximum strength, arm circumference, and biceps skinfold thickness were measured before and after training. One slow set increased strength by 25% (95% CI 13-36%, P < 0.001). Three sets of training produced greater increases in strength than one set (difference = 23% of initial strength, 95% CI 12-34%, P < 0.001) and fast training resulted in a greater increase in strength than slow training (difference = 11%, 95% CI 0.2-23%, P = 0.046). The interaction between sets and speed was negative (-15%) and of borderline significance (P = 0.052), suggesting there is a benefit of training with three sets or fast speeds, but there is not an additive benefit of training with both. Three sets of exercise produce twice the strength increase of one set in the early phase of resistance training. Training fast produces greater strength increases than training slow however, there does not appear to be any additional benefit of training with both three sets and fast contractions.
Publisher: Wiley
Date: 07-1991
DOI: 10.1113/JPHYSIOL.1991.SP018681
Abstract: 1. We investigated the possibility of a cortical contribution to human respiration by recording from the scalp of awake subjects the premotor cerebral potentials that are known to precede voluntary limb movements. 2. Electroencephalographic activity (EEG) was recorded from scalp electrodes and averaged for 1.8-2.0 s before the time at which airway pressure exceeded an inspiratory or expiratory threshold. Clear premotor cerebral potentials were recorded during brisk, self-paced nasal inhalations or exhalations. In ten subjects, a slow cortical negativity (Bereitschaftspotential) was apparent in the averaged EEG, commencing 1.2 +/- 0.3 s before the onset of inspiratory (scalene) or expiratory (abdominal) muscle activity (EMG). It was maximal at the vertex, with a mean slope of 12.3 +/- 5.8 microV/s, and was followed by a post-movement positivity. 3. In four subjects the inspiratory premotor potential culminated in a large negativity, the motor potential, which began 24 +/- 15 ms before the onset of scalene EMG. It is argued that such a short latency is consistent with a volitionally generated respiratory command which travels relatively directly to the respiratory muscles, having a total central delay which is no longer than that for voluntary finger movements. 4. That the respiratory premotor and motor potentials did not originate in subcortical structures was supported by their absence in a patient suffering from chronic reflexogenic hiccups, in whom cerebral activity was back-averaged from each brisk hiccup. 5. During quiet breathing, in which subjects were relaxed and distracted from thinking about their respiration, no premotor cerebral potentials preceding inspiration could be detected. This failure was not due to the slow rate of rise of inspiratory activity during quiet breathing as compared with a brisk sniff, because premotor potentials were detected when subjects intermittently generated slow active expiratory efforts. 6. These observations suggest that during quiet breathing the cerebral cortex does not contribute to respiratory drive on a breath-by-breath basis. Conversely, the presence of clear premotor cerebral potentials when subjects performed self-paced inspiratory or expiratory manoeuvres illustrates the powerful cortical projection to human respiratory muscles.
Publisher: American Physiological Society
Date: 04-2006
DOI: 10.1152/JAPPLPHYSIOL.01303.2005
Abstract: This is a study of the ability of blindfolded human subjects to match the position of their forearms before and after eccentric exercise. The hypothesis tested was that the sense of effort contributed to forearm position sense. The fall in force after the exercise was predicted to alter the relationship between effort and force and thereby induce position errors. In the arms-in-front posture, subjects had their unsupported reference arm set to one of two angles from the horizontal, 30 or 60°, and they matched its position by voluntary placement of their other arm. Matching errors were compared with a task where the arms were counterweighted, so could be moved in the vertical plane with minimal effort, and where the arms were moved in the horizontal plane. In these latter two tasks, the intention was to test whether removal of an effort sensation from holding the arm against gravity influenced matching performance. It was found that, although absolute errors for counterweighted and horizontal matching were no larger than for unsupported matching, their standard deviations, 6.1 and 6.8°, respectively, were significantly greater than for unsupported matching (4.6°), indicating more erratic matching. The eccentric exercise led, the next day, to a fall in maximum voluntary muscle torque of ≥15%. This was accompanied by a significant increase in matching errors for the unsupported matching task from 2.7 ± 0.5 to 0.8 ± 0.7° but not for counterweighted (1.4 ± 0.2 to −0.2°± 1.1°) or horizontal matching (−1.3 ± 0.7° to −1.8 ± 0.7°). This, it is postulated, is because the reduced voluntary torque after exercise was accompanied by a greater effort required to support the arms, leading to larger matching errors. However, effort is only able to provide positional information for unsupported matching where gravity plays a role. In gravity-neutral tasks like counterweighted or horizontal matching, a change in the effort-force relationship after exercise leaves matching accuracy unaffected.
Publisher: BMJ
Date: 09-1994
DOI: 10.1136/THX.49.9.881
Abstract: Although psychological distress predicts mortality in asthma, an underlying physiological link has not been shown. This study examined relations between impaired voluntary drive to breathe and measures of mood states. The level of maximal voluntary activation of the diaphragm and elbow flexors was measured in a previous study using a sensitive modification of the twitch interpolation technique in 11 asthmatic and 10 control subjects. In this study psychological distress was assessed using the Profile of Mood States questionnaire and measures of distress were compared with the muscle voluntary activation results. For the asthmatic subjects, depressed mood increased the risk of impaired maximal voluntary activation of the diaphragm by 3.5 times (95% CI 1.09 to 11.3). No such association was observed in control subjects. These results suggest that depressed mood may predispose an asthmatic patient to impaired voluntary activation of the diaphragm. Such in iduals would be at increased risk of rapidly developing ventilatory failure if faced with severe airway narrowing.
Publisher: Wiley
Date: 09-2008
Publisher: Springer Science and Business Media LLC
Date: 03-04-2003
DOI: 10.1007/S00221-003-1379-7
Abstract: A long-duration, submaximal contraction of a hand muscle increases central fatigue during a subsequent contraction in the other hand. However, this 'cross-over' of central fatigue between limbs is small and the location within the central nervous system at which this effect occurs is unknown. We investigated this 'cross-over' by measurement of the force and EMG responses to transcranial magnetic stimulation of the motor cortex (TMS). To produce central fatigue, we used sustained maximal voluntary contractions (MVCs). In the first study, subjects (n=10) performed four 1-min sustained MVCs of the elbow flexors, alternating between the left and right arms (two MVCs per arm). The sustained MVCs were performed consecutively with no rest periods. In the second study, the same subjects made two sustained 1-min MVCs with the same arm with a 1-min rest between efforts. During each sustained MVC, a series of TMS and brachial plexus stimuli were delivered. Surface EMG was recorded from biceps brachii and brachioradialis muscles bilaterally. Voluntary activation was estimated during each MVC using measurement of the force increments to TMS. On average during each sustained MVC, voluntary activation declined by 7-12% (absolute change, P<0.001) and voluntary force declined by 35-45% MVC (P<0.001), whereas the cortical motor-evoked potential increased (P<0.001) and the subsequent silent period lengthened (P<0.001). The average voluntary activation and voluntary force were similar during two sustained MVCs performed by the same arm, when separated by 1 min of rest. However, when the 1-min rest interval was replaced with a sustained contraction performed by the other arm, the average voluntary activation was 2.9% worse in the second contraction (absolute change, P<0.05), while it did not alter voluntary force production or the EMG responses to TMS. Therefore, in maximal exercise of 4 min duration, the 'cross-over' of central fatigue between limbs is small in the elbow flexors and has a minor functional effect. Our data suggest that voluntary drive from the motor cortex is slightly less able to drive the muscle maximally after a fatiguing voluntary contraction on the contralateral side.
Publisher: Wiley
Date: 16-01-2012
DOI: 10.1002/NBM.1801
Abstract: Muscle stiffness has been reported to increase following eccentric muscle exercise, but to date only indirect methods have been used to measure it. This study aimed to use Magnetic Resonance Elastography (MRE), a noninvasive imaging technique, to assess the time-course of passive elasticity changes in the medial gastrocnemius and soleus muscles before and after a bout of eccentric exercise. Shear storage modulus (G') and loss modulus (G'') measurements were made in eight healthy subjects for both muscles in vivo before, one hour after, 48 hours after and 1 week after eccentric exercise. The results show a 21% increase in medial gastrocnemius storage modulus following eccentric exercise with a peak occurring ~48 hours after exercise (before exercise 1.15 ± 0.23 kPa, 48 hours after 1.38 ± 0.27 kPa). No significant changes in soleus muscle storage modulus were measured for the exercise protocol used in this study, and no significant changes in loss modulus were observed. This study provides the first direct measurements in skeletal muscle before and after eccentric exercise damage and suggests that MRE can be used to detect the time course of changes to muscle properties.
Publisher: Frontiers Media SA
Date: 2011
Publisher: American Physiological Society
Date: 09-2005
Abstract: The neural mechanisms underlying the sense of joint position and movement remain controversial. While cutaneous receptors are known to contribute to kinesthesia for the fingers, the present experiments test the hypothesis that they contribute at other major joints. Illusory movements were evoked at the interphalangeal (IP) joints of the index finger, the elbow, and the knee by stimulation of populations of cutaneous and muscle spindle receptors, both separately and together. Subjects matched perceived movements with voluntary movements of homologous joints on the contralateral side. Cutaneous receptors were activated by stretch of the skin (using 2 intensities of stretch) and vibration activated muscle spindle receptors. Stimuli were designed to activate receptors that discharge during joint flexion. For the index finger, vibration was applied over the extensor tendons on the dorsum of the hand, to evoke illusory metacarpophalangeal (MCP) joint flexion, and skin stretch was delivered around the IP joints. The strong skin stretch evoked the illusion of flexion of the proximal IP joint in 6/8 subjects (12 ± 5°, mean ± SE). For the group, strong skin stretch delivered during vibration increased the perceived flexion of the proximal IP joint by eight times with a concomitant decrease in perceived flexion of the MCP joint compared with vibration alone ( P 0.05). For the elbow, vibration was applied over the distal tendon of triceps brachii and skin stretch over the dorsal forearm. When delivered alone, strong skin stretch evoked illusory elbow flexion in 5/10 subjects (9 ± 4°). Simultaneous strong skin stretch and vibration increased the illusory elbow flexion for the group by 1.5 times compared with vibration ( P 0.05). For the knee, vibration was applied over the patellar tendon and skin stretch over the thigh. Skin stretch alone evoked illusory knee flexion in 3/10 subjects (8 ± 4°) and when delivered during vibration, perceived knee flexion increased for the group by 1.4 times compared with vibration ( P 0.05). Hence inputs from cutaneous receptors, muscle receptors, and combined inputs from both receptors likely subserve kinesthesia at joints throughout the body.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 02-2006
DOI: 10.1016/J.PAIN.2005.11.003
Abstract: All pain is unpleasant, but different perceptual and emotional qualities are characteristic of pain originating in different structures. Pain of superficial (cutaneous) origin usually is sharp and restricted, whereas pain of deep origin (muscle/viscera) generally is dull and diffuse. Despite the differences it has been suggested previously that all pain is mediated by an invariant set ("neuromatrix") of brain structures. However, we report here, using functional magnetic resonance imaging (fMRI), that striking regional differences in brain activation patterns were the rule. Signal differences were found in regions implicated in emotion (perigenual cingulate cortex), stimulus localization and intensity (somatosensory cortex) and motor control (motor cortex, cingulate motor area). Further, most fMRI signal changes matched perceived changes in pain intensity. These findings clearly indicate that distinct neural activity patterns in distinct sets of brain structures are evoked by pain originating from different tissues of the body. Further, we suggest that these differences underlie the different perceptual and emotional reactions evoked by deep versus superficial pain.
Publisher: Wiley
Date: 08-2005
Publisher: Wiley
Date: 28-11-2019
DOI: 10.1113/JP278630
Abstract: How we judge the location of our body parts can be affected by a range of factors that change how our brain interprets proprioceptive signals. We examined the effect of several such factors on how we perceive an object's width and the spacing between our thumb and fingers when grasping. Grasp‐related perceptions were slightly wider when using all digits, in line with our tendency to grasp larger objects with the entire hand. Surprisingly, these perceptions were not affected by the frames of reference for judgements (object width versus grasp aperture), whether the object was grasped actively or passively, or the strength of the grasp. These results show that the brain maintains a largely stable representation of the hand when grasping stationary objects. This stability may underpin our dexterity when grasping a vast array of objects. Various factors can alter how the brain interprets proprioceptive signals, leading to errors in how we perceive our body and execute motor tasks. This study determined the effect of critical factors on hand‐based perceptions. In Experiment 1, 20 participants grasped without lifting an unseen 6.5 cm‐wide object with two grasp configurations: thumb and all fingers, and thumb and index finger. Participants reported perceived grasp aperture (body reference frame) or perceived object width (external reference frame) using visual charts. In Experiment 2, 20 participants grasped the object with three grasp intensities (1, 5 and 15% maximal grasp force) actively or passively and reported perceived grasp aperture. A follow‐up experiment addressed whether results from Experiment 2 were influenced by the external force applied during passive grasp. Overall, there was a mean difference of 0.38 cm (95% confidence interval (CI), 0.12 to 0.63) between the two grasp configurations (all digits compared to thumb and index finger). Perceived object width compared to perceived grasp aperture differed by only −0.04 cm (95% CI, −0.30 to 0.21). There was no real effect of grasp intensity on perceived grasp aperture (−0.01 cm 95% CI, −0.03 to 0.01) or grasp type (active versus passive 0.18 cm 95% CI, −0.19 to 0.55). Overall, grasp‐related perceptions are slightly wider when using all digits, in line with our tendency to grasp larger objects with the entire hand. The other factors – frame of reference, grasp intensity and grasp type – had no meaningful effect on these perceptions. These results provide evidence that the brain maintains a largely stable representation of the hand.
Publisher: Public Library of Science (PLoS)
Date: 17-01-2019
Publisher: Elsevier BV
Date: 06-2002
Abstract: To examine the contributions of sensorimotor factors to postural control and falling in people with prior polio and to determine whether these contributions differ from those found in normal populations. Survey and case-control study. A falls and balance laboratory in Australia. Forty persons with prior polio (age range, 28-71 y) and 38 age- and sex-matched control subjects. Not applicable. Lower-limb muscle strength, sway, vision, lower-limb sensation, reaction time, foot-tapping speed, and falls. Compared with the control subjects, the prior polio subjects performed similarly in sensory tests but worse in tests that involved a motor component. Within the prior polio group, lower-limb strength was strongly associated with postural sway on a compliant surface and explained more of the variance in sway than in control subjects. Prior polio subjects who fell multiple times had reduced lower-limb strength, slower reaction time, lower foot-tapping speed, and increased sway compared with those who fell less often. However, the rate of decline in lower-limb strength within the prior polio group did not exceed normal, age-related changes. This investigation of prior polio subjects provides an appropriate model for studying muscle weakness as a falls risk factor. Weakness was directly associated with falls, and had an indirect effect mediated through increased sway.
Publisher: Public Library of Science (PLoS)
Date: 13-06-2016
Publisher: Wiley
Date: 08-1988
DOI: 10.1113/JPHYSIOL.1988.SP017208
Abstract: 1. Microneurographic techniques were employed to record unitary activity from afferents associated with digital joints of six conscious human subjects. Of 120 single afferents s led from the median and ulnar nerves at the wrist, eighteen (15%) were classified as joint afferents the majority of the s le (72.5%) were of cutaneous origin, and 12.5% were from muscle spindles and tendon organs. 2. Of the eighteen joint afferents six were tonically active in the rest position of the hand. All except two were recruited or accelerated their background discharge during passive joint movement. Three tonically active afferents were responsive to passive movement throughout the physiological range. The majority of the afferents, including the other three tonically active units, responded only towards the limits of joint rotation. 3. As a group, the s le of joint afferents had a limited capacity to signal the direction of joint movement. Nine of the sixteen joint afferents sensitive to movement responded in two axes of angular displacement, and two responded in all three axes. In any one axis of rotation eight afferents were activated in both directions of movement. However, one afferent, associated with the interphalangeal joint of the thumb, responded uni-directionally throughout the physiological range of joint movement and was thereby capable of adequately encoding joint position and movement. 4. Twenty-one of twenty-nine slowly adapting and eleven of eighteen rapidly adapting cutaneous afferents tested were activated by joint movement, but only towards the limits of joint rotation half of the thirty-two movement-sensitive afferents were bi-directionally responsive. Muscle spindle afferents responded to stresses applied to the joint only if the resulting passive movement stretched the parent muscle. 5. It is concluded that human joint afferents possess a very limited capacity to provide kinaesthetic information, and that this is likely to be of significance only when muscle spindle afferents cannot contribute to kinaesthesia.
Publisher: American Physiological Society
Date: 15-05-2015
DOI: 10.1152/JAPPLPHYSIOL.01103.2014
Abstract: This study assessed the effects of inhaled lignocaine to reduce upper airway surface mechanoreceptor activity on 1) basal genioglossus and tensor palatini EMG, 2) genioglossus reflex responses to large pulses (∼10 cmH 2 O) of negative airway pressure, and 3) upper airway collapsibility in 15 awake in iduals. Genioglossus and tensor palatini muscle EMG and airway pressures were recorded during quiet nasal breathing and during brief pulses (250 ms) of negative upper-airway pressure. Lignocaine reduced peak inspiratory (5.6 ± 1.5 vs. 3.8 ± 1.1% maximum mean ± SE, P 0.01) and tonic (2.8 ± 0.8 vs. 2.1 ± 0.7% maximum P 0.05) genioglossus EMG during quiet breathing but had no effect on tensor palatini EMG (5.0 ± 0.8 vs. 5.0 ± 0.5% maximum P = 0.97). Genioglossus reflex excitation to negative pressure pulses decreased after anesthesia (60.9 ± 20.7 vs. 23.6 ± 5.2 μV P 0.05), but not when expressed as a percentage of the immediate prestimulus baseline. Reflex excitation was closely related to the change in baseline EMG following lignocaine ( r 2 = 0.98). A short-latency genioglossus reflex to rapid increases from negative to atmospheric pressure was also observed. The upper airway collapsibility index (%difference) between nadir choanal and epiglottic pressure increased after lignocaine (17.8 ± 3.7 vs. 28.8 ± 7.5% P 0.05). These findings indicate that surface receptors modulate genioglossus but not tensor palatini activity during quiet breathing. However, removal of input from surface mechanoreceptors has minimal effect on genioglossus reflex responses to large (∼10 cmH 2 O), sudden changes in airway pressure. Changes in pressure rather than negative pressure per se can elicit genioglossus reflex responses. These findings challenge previous views and have important implications for upper airway muscle control.
Publisher: American Physiological Society
Date: 12-2010
Abstract: Flexor digitorum profundus (FDP), the sole flexor of the fingertips, is critical for tasks such as grasping. It is a compartmentalized multitendoned muscle with both neural and mechanical links between the fingers. We determined whether voluntary activation (VA), the level of neural drive to muscle, could be measured separately in its four compartments, whether VA differed between the fingers, and whether maximal voluntary contraction (MVC) force and VA changed when the non-test fingers were extended from full flexion to 90° flexion to partially “disengage” the test finger. Transcranial magnetic stimulation (TMS) of the motor cortex was used to measure VA, in a position in which only FDP generated force at the fingertip. Despite differences among the fingers in MVCs, VA for each finger was ∼92% ( n = 8), with no differences between fingers. When the test finger was partially disengaged by extending the other fingers to 90° flexion, performance was more variable both within and between subjects. MVCs decreased significantly by about 25–40% for the four fingers. However, VA was not significantly changed ( n = 6) and was similar for the four fingers. In both positions, there were strong linear relationships between the voluntary forces and the superimposed twitch sizes, indicating that the method to measure VA was very reliable. Our results indicate that maximal VA is similar for all four compartments of FDP when force production by the other fingers is unconstrained. When altered mechanical connections between the compartments decrease voluntary force output there is little difference in neural drive.
Publisher: American Physiological Society
Date: 06-2006
Publisher: Wiley
Date: 04-10-2013
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 10-2013
DOI: 10.1016/J.PAIN.2013.05.024
Abstract: Pain is fundamental to survival, as are our perceptions of the environment. It is often assumed that we see our world as a read-out of the sensory information that we receive yet despite the same physical makeup of our surroundings, in iduals perceive differently. What if we "see" our world differently when we experience pain? Until now, the causal effect of experimental pain on the perception of an external stimulus has not been investigated. Eighteen (11 female) healthy volunteers participated in this randomised repeated-measures experiment, in which participants estimated the distance to a switch placed on the table in front of them. We varied whether or not the switch would instantly stop a stimulus, set to the participant's pain threshold, being delivered to their hand, and whether or not they were required to reach for the switch. The critical result was a strong interaction between reaching and pain [F(1,181)=4.8, P=0.03], such that when participants experienced pain and were required to reach for a switch that would turn off the experimental stimulus, they judged the distance to that switch to be closer, as compared to the other 3 conditions (mean of the true distance 92.6%, 95% confidence interval 89.7%-95.6%). The judged distance was smaller than estimates in the other 3 conditions (mean±SD difference >5.7%±2.1%, t(181) >3.5, P<0.01 for all 3 comparisons). We conclude that the perception of distance to an object is modulated by the behavioural relevance of the object to ongoing pain.
Publisher: American Physiological Society
Date: 10-2008
DOI: 10.1152/JAPPLPHYSIOL.01246.2007
Abstract: This study compared the contribution of supraspinal fatigue to muscle fatigue in old and young adults. Transcranial magnetic stimulation (TMS) of motor cortex was used to assess voluntary activation during maximal voluntary contractions (MVCs) of elbow flexor muscles in 17 young adults (25.5 ± 3.6 yr mean ± SD) and 7 old adults (73.0 ± 3.3 yr). Subjects performed a fatigue task involving six sustained MVCs (22-s duration, separated by 10 s). Young adults exhibited greater reductions in maximal voluntary torque (67 ± 15% of baseline) than the old (37 ± 6% P 0.001). Increments in torque (superimposed twitch) generated by TMS during sustained MVCs increased for the young and old ( P 0.001) but were larger for the old adults at the start of the sustained contractions and during recovery ( P 0.05). Voluntary activation was less for the old adults at the start of some sustained contractions and during recovery ( P = 0.02). Motor-evoked potential area increased similarly with age during the fatiguing task but was greater for the old adults than young during recovery. Silent period duration lengthened less for the old adults during the fatigue task. At the end of the fatiguing task, peak relaxation rate of muscle fibers had declined more in the young than the old adults. The greater endurance with age is largely due to a difference in mechanisms located within the muscle. However, recovery from the fatiguing exercise is impaired for old adults because of greater supraspinal fatigue than in the young.
Publisher: Springer Science and Business Media LLC
Date: 12-01-2010
DOI: 10.1038/SC.2009.191
Abstract: A randomized controlled trial. To determine the effectiveness of electrical stimulation (ES)-evoked muscle contractions superimposed on progressive resistance training (PRT) for increasing voluntary strength in the quadriceps muscles of people with spinal cord injuries (SCI). Sydney, Australia. A total of 20 people with established SCI and neurologically induced weakness of the quadriceps muscles participated in the trial. Participants were randomized between experimental and control groups. Volunteers in the experimental group received ES superimposed on PRT to the quadriceps muscles of one leg thrice weekly for 8 weeks. Participants in the control group received no intervention. Assessments occurred at the beginning and at the end of the 8-week period. The four primary outcomes were voluntary strength (Nm) and endurance (fatigue ratio) as well as the performance and satisfaction items of the Canadian Occupational Performance Measure (COPM points). The between-group mean differences (95% confidence interval (CI)) for voluntary strength and endurance were 14 Nm (1-27 P=0.034) and 0.1 (-0.1 to 0.3 P=0.221), respectively. The between-group median differences (95% CI) for the performance and satisfaction items of the COPM were 1.7 points (-0.2 to 3.2 P=0.103) and 1.4 points (-0.1 to 4.6 P=0.058), respectively. ES superimposed on PRT improves voluntary strength, although there is uncertainty about whether the size of the treatment effect is clinically important. The relative effectiveness of ES and PRT is yet to be determined.
Publisher: American Physiological Society
Date: 02-2007
DOI: 10.1152/JAPPLPHYSIOL.00683.2006
Abstract: Neural drive to inspiratory pump muscles is increased under many pathological conditions. This study determined for the first time how neural drive is distributed to five different human inspiratory pump muscles during tidal breathing. The discharge of single motor units ( n = 280) from five healthy subjects in the diaphragm, scalene, second parasternal intercostal, third dorsal external intercostal, and fifth dorsal external intercostal was recorded with needle electrodes. All units increased their discharge during inspiration, but 41 (15%) discharged tonically throughout expiration. Motor unit populations from each muscle differed in the timing of their activation and in the discharge rates of their motor units. Relative to the onset of inspiratory flow, the earliest recruited muscles were the diaphragm and third dorsal external intercostal (mean onset for the population after 26 and 29% of inspiratory time). The fifth dorsal external intercostal muscle was recruited later (43% of inspiratory time P 0.05). Compared with the other inspiratory muscles, units in the diaphragm and third dorsal external intercostal had the highest onset (7.7 and 7.1 Hz, respectively) and peak firing frequencies (12.6 and 11.9 Hz, respectively both P 0.05). There was a unimodal distribution of recruitment times of motor units in all muscles. Neural drive to human inspiratory pump muscles differs in timing, strength, and distribution, presumably to achieve efficient ventilation.
Publisher: American Physiological Society
Date: 12-2020
DOI: 10.1152/JAPPLPHYSIOL.00610.2020
Abstract: When the inspiratory muscles are fatigued with repeated sustained maximal efforts, supraspinal fatigue, a component of central fatigue, contributes to the loss in maximal inspiratory pressure. The presence of supraspinal fatigue was confirmed by the increase in litude of twitch-like increments in pressure evoked by motor cortical stimulation during maximal efforts, indicating that motor cortical output was not maximal as extra muscle force could be generated to increase inspiratory pressure.
Publisher: Wiley
Date: 18-12-2017
DOI: 10.1113/JP274781
Publisher: American Physiological Society
Date: 04-2011
DOI: 10.1152/JAPPLPHYSIOL.00454.2010
Abstract: Maintenance of airway patency during breathing involves complex interactions between pharyngeal dilator muscles. The few previous studies of geniohyoid activity using multiunit electromyography (EMG) have suggested that geniohyoid shows predominantly inspiratory phasic activity. This study aimed to quantify geniohyoid respiration-related activity with single motor unit (SMU) EMG recordings. Six healthy subjects of normal body mass index were studied. Intramuscular EMG recordings of geniohyoid activity were made with a monopolar needle with subjects in supine and seated positions. The depth of the geniohyoid was identified by ultrasound, and the electrode position was confirmed with maneuvers to isolate activity in geniohyoid and genioglossus. Activity was recorded at 85 sites in the geniohyoid during quiet breathing (45 supine and 40 seated). When subjects were supine, 33 sites (73%) showed no activity during breathing and 10 (22%) showed tonic activity. In addition, one site showed a tonic SMU with increased expiratory discharge, and one site in another subject had one unit with expiratory phasic activity. When subjects were seated, 27 sites (68%) in the geniohyoid showed no activity, 12 sites (30%) showed tonic activity that was not respiration related, and one unit at one site showed phasic expiratory activity. The average peak discharge frequency of geniohyoid motor units was 16.2 ± 3.1 impulses/s during the “geniohyoid maneuver,” which was the first part of a swallow. In contrast to previous findings, the geniohyoid shows some tonic activity but minimal respiration-related activity in healthy subjects in quiet breathing. The geniohyoid has little active role in airway stability under these conditions.
Publisher: BMJ
Date: 09-1986
Abstract: Maximal voluntary strength (torque) of the flexors and extensors of the elbow was measured in 56 normal subjects and 18 hemiparetic subjects. In normal subjects the ratio of extension to flexion strength averaged 55% and did not differ significantly between sides or sexes. The ratio of maximal extensor to flexor strength on the clinically unaffected side of hemiparetic subjects was the same as that for the normal subjects but it was significantly increased on the affected side. This increase indicates that the elbow flexors were relatively more weakened than the extensors on the hemiparetic side, a conclusion contrary to conventional clinical teaching. The increase in the ratio was not the result of co-contraction of either muscle group. A possible physiological basis for the observed distribution of weakness is suggested.
Publisher: American Physiological Society
Date: 03-2010
Abstract: The corticospinal pathway is the major pathway controlling human voluntary movements. After strong voluntary contractions, the efficacy of corticospinal transmission to elbow flexors is reduced for ∼90 s, and this limits motoneuronal output. This reduction may reflect activity-dependent changes at cortico-motoneuronal synapses. We investigated whether similar changes occur in a leg muscle, tibialis anterior (TA). Electrical stimuli over high thoracic vertebrae activated corticospinal axons to evoke an EMG response in TA (TMEP). Stimuli were delivered before and after short 10-s and prolonged 1-min maximal contractions (MVCs) of ankle dorsiflexors. In two studies, stimuli were given with the muscle relaxed. In other studies, stimuli were given during weak contraction. After a 10-s MVC ( study 1, n = 10), TMEPs increased immediately to 349 ± 335% (mean ± SD) of control values. By 1 min after contraction, TMEPs decreased to 38 ± 28% of control and remained depressed for min. Facilitation (191 ± 133% control) and depression (18 ± 22% control) occurred over the same time course after the 1-min MVC ( study 2, n = 10). When tested during weak contraction ( study 3, n = 10), TMEPs showed less facilitation (131 ± 41% control) and less depression (67 ± 21% control) and responses returned to baseline over ∼15 min. In contrast to TMEPs, H-reflexes in TA were little changed after a 10-s MVC ( study 4, n = 7). Our findings reveal an immediate facilitation and subsequent longer-lasting depression in corticospinal transmission to TA, which originate at a premotoneuronal site. This behavior differs markedly from that in elbow flexor muscles and suggests that activity-dependent changes in the motor pathway may be muscle specific.
Publisher: American Physiological Society
Date: 02-2009
DOI: 10.1152/JAPPLPHYSIOL.90939.2008
Abstract: Control of posture and movement requires control of the output from motoneurons. Motoneurons of human lower limb muscles exhibit sustained, submaximal activity to high-frequency electrical trains, which has been hypothesized to be partly triggered by monosynaptic Ia afferents. The possibility to trigger such behavior in upper limb motoneurons and the potential unique role of Ia afferents to trigger such behavior remain unclear. Subjects ( n = 9) received high-frequency trains of electrical stimuli over biceps brachii and flexor pollicis longus (FPL). We chose to study the FPL muscle because it has weak monosynaptic Ia afferent connectivity and it is involved in fine motor control of the thumb. Two types of stimulus trains (100-Hz bursts and triangular r s) were tested at five intensities below painful levels. All subjects exhibited enhanced torque in biceps and FPL muscles after both types of high-frequency train. Torques also persisted after stimulation, particularly for the highest stimulus intensity. To separate the evoked torques that resulted from a peripheral mechanism (e.g., muscle potentiation) and that which resulted from a central origin, we studied FPL responses to high-frequency trains after complete combined nerve blocks of the median and radial nerves ( n = 2). During the blocks, high-frequency trains over the FPL did not yield torque enhancements or persisting torques. These results suggest that enhanced contractions of central origin can be elicited in motoneurons innervating the upper limb, despite weak monosynaptic Ia connections for FPL. Their presence in a recently evolved human muscle (FPL) indicates that these enhanced contractions may have a broad role in controlling tonic postural outputs of hand muscles and that they may be available even for fine motor activities involving the thumb.
Publisher: Springer International Publishing
Date: 2014
Publisher: Wiley
Date: 16-07-2012
DOI: 10.1002/MUS.23356
Abstract: In this study we compared passive mechanical properties of gastrocnemius muscle-tendon units, muscle fascicles, and tendons in control subjects and people with ankle contractures after spinal cord injury. Passive gastrocnemius length-tension curves were derived from passive ankle torque-angle data obtained from 20 spinal cord injured subjects with ankle contractures and 30 control subjects. Ultrasound images of muscle fascicles were used to partition length-tension curves into fascicular and tendinous components. Spinal cord injured subjects had stiffer gastrocnemius muscle-tendon units (stiffness index: 74.8 ± 27.0 m(-1) ) than control subjects (54.4 ± 17.7 m(-1) ) (P = 0.004). Muscle-tendon slack lengths, as well as slack lengths and changes in length of fascicles and tendons, were similar in the two groups. People with ankle contractures after spinal cord injury have stiff gastrocnemius muscle-tendon units. It is not clear whether this reflects changes in properties of muscle fascicles or tendons.
Publisher: American Physiological Society
Date: 10-2003
Abstract: Motor or sensory activity in one arm can affect the other arm. We tested the hypothesis that a voluntary contraction can affect the motor pathway to the contralateral homologous muscle and investigated whether alterations in sensory input might mediate such effects. Responses to transcranial magnetic stimulation [motor-evoked potentials (MEPs)], stimulation of the descending tracts [cervicomedullary MEPs (CMEPs)], and peripheral nerve stimulation (H-reflex) were recorded from the relaxed right flexor carpi radialis (FCR), while the left arm underwent unilateral interventions (5 s duration) that included voluntary contraction, muscle contraction evoked through percutaneous stimulation, tendon vibration, and cutaneous and mixed nerve stimulation. During moderate to strong voluntary wrist flexion on the left, MEPs in the right FCR increased, CMEPs were unaffected, and the H-reflex was depressed. These results are consistent with an increase in excitability of the motor cortex, no effect on the motoneuron pool, and presynaptic inhibition of Ia afferents. In contrast, percutaneous muscle stimulation facilitated both MEPs and the H-reflex. However, muscle contraction produced by a combination of voluntary effort and electrical stimulation also reduced the contralateral H-reflex. After voluntary contractions, the H-reflex remained depressed for 35 s, but after stimulationevoked contractions, it rapidly returned to baseline. Under both conditions, MEPs recovered rapidly. After voluntary contractions, CMEPs were also depressed for approximately 10 s despite their lack of change during contractions. Wrist tendon vibration (100 Hz) did not affect, and 20-Hz median nerve stimulation or forearm medial cutaneous nerve stimulation mildly facilitated, the H-reflex without affecting MEPs. Voluntary wrist extension, similarly to wrist flexion, increased MEPs and depressed H-reflexes. However, ankle dorsiflexion facilitated the H-reflex akin to the Jendrassik maneuver. These data suggest that a unilateral voluntary muscle contraction has contralateral effects at both cortical and segmental levels and that the segmental effects are not replicated by stimulated muscle contraction or by input from muscle spindles or non-nociceptive cutaneous afferents.
Publisher: Elsevier BV
Date: 02-2000
DOI: 10.1016/S0006-3223(99)00285-1
Abstract: Carefully designed controlled studies are essential in further evaluating the therapeutic efficacy of transcranial magnetic stimulation (TMS) in psychiatric disorders. A major methodological concern is the design of the "sham" control for TMS. An ideal sham would produce negligible cortical stimulation in conjunction with a scalp sensation akin to real treatment. Strategies employed so far include alterations in the position of the stimulating coil, but there has been little systematic study of their validity. In this study, we investigated the effects of different coil positions on cortical activation and scalp sensation. In nine normal subjects, single TMS pulses were administered at a range of intensities with a "figure eight" coil held in various positions over the left primary motor cortex. Responses were measured as motor-evoked potentials in the right first dorsal interosseus muscle. Scalp sensation to TMS with the coil in various positions over the prefrontal area was also assessed. None of the coil positions studied met the criteria for an ideal sham. Arrangements associated with a higher likelihood of scalp sensation were also more likely to stimulate the cortex. The choice of a sham for TMS involves a trade-off between effective blinding and truly inactive "stimulation." Further research is needed to develop the best sham condition for a range of applications.
Publisher: SAGE Publications
Date: 16-10-2014
Abstract: Background. Surface electrical stimulation of the abdominal muscles, with electrodes placed in the posterolateral position, combined with a voluntary cough can assist clearance of airway secretions in in iduals with high-level spinal cord injury (SCI). Objective. To determine whether an increase in stimulus intensity of the trains of electrical stimuli delivered to the expiratory muscles has an increasing effect on a stimulated voluntary cough and to determine at which stimulus intensity a plateau of cough peak expiratory flow occurs. Methods. In 7 healthy in iduals with a SCI at and above C7, gastric pressure ( P ga ), esophageal pressure ( P es ), peak expiratory cough flow (PEF cough ), and expiratory volume were measured as participants coughed voluntarily with simultaneous trains of electrical stimuli delivered over the abdominal muscles (50 Hz, 1-s duration). The intensity of the stimulation was increased incrementally. Results: A plateau in PEF cough occurred in all 7 in iduals at a mean of 211 ± 29 mA (range 120-360 mA). Peak values reached for P ga , P es , and PEF cough were 83.0 ± 8.0 cm H 2 O, 66.1 ± 5.6 cm H 2 O, and 4.0 ± 0.4 l/s respectively. Conclusions. The plateau in expiratory cough flow that was associated with increasing expiratory pressures is indicative of dynamic airway compression. This suggests that the evoked cough will be effective in creating more turbulent airflow to further assist in dislodging mucus and secretions.
Publisher: Wiley
Date: 04-10-2016
DOI: 10.1111/APHA.12792
Abstract: Knowledge of which body parts belong to us is referred to as the sense of body ownership. There is increasing evidence that this important aspect of human proprioception is highly malleable. Research into ownership of in idual body parts was stimulated by Botvinick and Cohen's rubber-hand illusion (Nature 391,1998, 756), which demonstrated that an artificial body part can be incorporated in one's body representation and can cause real body parts to be sensed erroneously. Here, we review key studies that have advanced our understanding of the sense of body ownership, including the important role played by multisensory integration and spatiotemporal congruence of sensory signals. We also discuss our recent discovery that body ownership can be induced in response to movement stimuli by signals from a single class of sensory receptor, namely muscle spindles.
Publisher: Frontiers Media SA
Date: 2012
Publisher: Wiley
Date: 28-09-2012
Publisher: Wiley
Date: 08-2019
DOI: 10.1113/JP278335
Publisher: Wiley
Date: 28-10-2011
Publisher: Wiley
Date: 17-12-2016
DOI: 10.1113/JP273200
Publisher: Wiley
Date: 09-2003
Publisher: Wiley
Date: 10-1990
DOI: 10.1113/JPHYSIOL.1990.SP018247
Abstract: 1. Microneurographic techniques were used to isolate single afferent axons within cutaneous and motor fascicles of the median and ulnar nerves at the wrist in thirteen subjects. Of the sixty-five identified afferents, eleven innervated the interphalangeal and metacarpophalangeal joints, sixteen innervated muscle spindles, three innervated Golgi tendon organs and thirty-five supplied the glabrous skin of the hand. 2. Intrafascicular stimulation through the recording microelectrode, using trains of constant-voltage positive pulses (0.3-0.8 V, 0.1-0.2 ms, 1-100 Hz) or constant-current biphasic pulses (0.4-13.0 microA, 0.2 ms, 1-100 Hz), evoked specific sensations from sites associated with some afferent species but not others. 3. Microstimulation of eight of the eleven joint afferent sites (73%) evoked specific sensations. With four, subjects reported innocuous deep sensations referred to the relevant joint. With the other four, the subjects reported a sensation of joint displacement that partially reflected the responsiveness of the afferents to joint rotation. 4. Microstimulation of fourteen of the sixteen muscle spindle afferent sites (88%) generated no perceptions when the stimuli did not produce overt movement. However, subjects could correctly detect the slight movements generated when the stimuli excited the motor axons to the parent muscle. 5. With seven of the nine rapidly adapting (type RA or FAI) cutaneous afferents (88%) microstimulation evoked sensations of 'flutter-vibration', and with two of eight slowly adapting (type SAI) afferents (25%) it evoked sensations of 'sustained pressure'. Of the eighteen SAII afferents, which were classified as such by their responses to planar skin stretch, the majority (83%) generated no perceptions, confirming previous work, but three evoked sensations of movements or pressure. 6. The present results suggest a relatively secure transmission of joint afferent traffic to perceptual levels, and it is concluded that the human brain may be able to synthesize meaningful information on joint displacement on the basis of impulses in a single joint afferent. This could partly compensate for the low responsiveness of in idual joint afferents within the physiological range of joint displacements. Although single muscle spindle afferents can adequately encode joint position and movement, the results suggest that the brain needs the information from more than one muscle spindle afferent to perceive changes in joint angle.
Publisher: Frontiers Media SA
Date: 13-05-2015
Publisher: Wiley
Date: 08-2005
Publisher: American Physiological Society
Date: 08-2008
Abstract: These studies investigated whether a single electrical stimulus over the thoracic spine activates corticospinal axons projecting to human leg muscles. Transcranial magnetic stimulation of the motor cortex and electrical stimulation over the thoracic spine were paired at seven interstimulus intervals, and surface electromyographic responses were recorded from rectus femoris, tibialis anterior, and soleus. The interstimulus intervals (ISIs) were set so that the first descending volley evoked by cortical stimulation had not arrived at (positive ISIs), was at the same level as (0 ISI) or had passed (negative ISIs) the site of activation of descending axons by the thoracic stimulation at the moment of its delivery. Compared with the responses to motor cortical stimulation alone, responses to paired stimuli were larger at negative ISIs but reduced at positive ISIs in all three leg muscles. This depression of responses at positive ISIs is consistent with an occlusive interaction in which an antidromic volley evoked by the thoracic stimulation collides with descending volleys evoked by cortical stimulation. The cortical and spinal stimuli activate some of the same corticospinal axons. Thus it is possible to examine the excitability of lower limb motoneuron pools to corticospinal inputs without the confounding effects of changes occurring within the motor cortex.
Publisher: American Psychiatric Association Publishing
Date: 06-1999
Abstract: The efficacy and safety of left prefrontal repetitive transcranial magnetic stimulation (rTMS) for treating resistant major depression were examined in a double-blind, controlled study. Eighteen medication-resistant depressed subjects were randomly assigned to 2 weeks of real or sham rTMS, then permitted up to 4 weeks of real rTMS. Effects on mood, neuropsychological function, EEG, and hearing were assessed. The groups receiving real and sham rTMS improved in mood significantly over the 2-week double-blind period, but there was no significant difference between groups. Repetitive transcranial magnetic stimulation did not provide significantly greater improvement than did sham treatment. A 4-week course of rTMS, as administered in this study, was safe.
Publisher: Elsevier BV
Date: 05-2007
DOI: 10.1016/J.JNEUMETH.2007.01.006
Abstract: The neural control of important rhythmical processes such as breathing and locomotion is complex. It is often necessary to depict the activity of motor (or other) units throughout the cycles. We describe and illustrate a novel method that displays visually seven key variables in a single figure related to the timing and frequencies of the discharge of single motor units. This time-and-frequency plot (TAFPLOT) displays the recruitment time, time of peak discharge frequency and derecruitment time, as well as the onset, peak, and final firing frequencies of each motor unit in a population. The frequency of any tonic firing is also displayed. Using the TAFPLOT it is easy to identify the presence or absence of coordinated activity within and between different motoneuron pools. The method is used to illustrate novel differences in the discharge behavior between populations of single motor units innervating the human diaphragm and genioglossus muscles. This new display provides a simple, qualitative and quantitative tool to study the neural control of rhythmical or repetitive motor tasks.
Publisher: Wiley
Date: 28-02-2013
Publisher: American Physiological Society
Date: 05-2021
DOI: 10.1152/JAPPLPHYSIOL.00557.2020
Abstract: Muscle activity is often normalized to maximal muscle activity however, it is difficult to obtain accurate measures of maximal muscle activity in people with impaired voluntary neural drive. We determined the relationship between voluntary muscle activation and plantarflexor muscle activity across a broad range of muscle activation values in able-bodied people. The relationship between voluntary muscle activation and muscle activity can be described with simple mathematical functions capable of estimating maximal muscle activity.
Publisher: American Physiological Society
Date: 02-2013
DOI: 10.1152/JAPPLPHYSIOL.00539.2013
Abstract: The upper airway is a complex, multifunctional, dynamic neuromechanical system. Its patency during breathing requires moment-to-moment coordination of neural and mechanical behavior and varies with posture. Failure to continuously recruit and coordinate dilator muscles to counterbalance the forces that act to close the airway results in hypopneas or apneas. Repeated failures lead to obstructive sleep apnea (OSA). Obesity and anatomical variations, such as retrognathia, increase the likelihood of upper airway collapse by altering the passive mechanical behavior of the upper airway. This behavior depends on the mechanical properties of each upper airway tissue in isolation, their geometrical arrangements, and their physiological interactions. Recent measurements of respiratory-related deformation of the airway wall have shown that there are different patterns of airway soft tissue movement during the respiratory cycle. In OSA patients, airway dilation appears less coordinated compared with that in healthy subjects (matched for body mass index). Intrinsic mechanical properties of airway tissues are altered in OSA patients, but the factors underlying these changes have yet to be elucidated. How neural drive to the airway dilators relates to the biomechanical behavior of the upper airway (movement and stiffness) is still poorly understood. Recent studies have highlighted that the biomechanical behavior of the upper airway cannot be simply predicted from electromyographic activity (electromyogram) of its muscles.
Publisher: Wiley
Date: 09-2007
Publisher: Wiley
Date: 08-05-2021
DOI: 10.1113/JP281614
Publisher: Wiley
Date: 28-06-2008
Publisher: Wiley
Date: 2004
DOI: 10.1002/MUS.20094
Abstract: To examine the long-term effects of polio, maximal voluntary strength and voluntary activation of elbow flexor muscles of 177 patients from a postpolio clinic were investigated using twitch interpolation. Muscle endurance was studied in 142 patients during 45 min of submaximal exercise, and predictors of impaired muscle performance were investigated. Twenty-nine of 177 patients (16.4%) had impaired voluntary drive to their elbow flexor muscles, but only 16 (9.0%) had markedly reduced elbow flexor strength, despite 74 (41.8%) reporting they were initially affected in their tested limb and 172 (97.2%) patients reporting new generalized symptoms. Seven patients had impaired muscle endurance in the tests of strength and voluntary drive. During the submaximal exercise, 16 patients (11.3%) had impaired peripheral muscle endurance with normal voluntary activation. These results confirm a low incidence of impaired upper-limb muscle performance in postpolio patients, despite many patients having subjective symptoms consistent with postpolio syndrome. There was an increased relative risk for impaired muscle function in those patients with a subjective decrease in strength in the tested limb, a recent decline in activities of daily living in their tested limb, and who used orthotic devices in their tested limb. Monitoring of function in prior-polio patients with impaired muscle performance may be useful, particularly when combined with investigation of other potential contributory factors to the functional impairment.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 12-2001
Publisher: SAGE Publications
Date: 15-10-2010
Abstract: Background. Spinal cord injury (SCI) patients have respiratory complications because of abdominal muscle weakness and paralysis, which impair the ability to cough. Objective. This study aims to enhance cough in high-level SCI subjects (n = 11, SCI at or above T6) using surface electrical stimulation of the abdominal muscles via 2 pairs of posterolaterally placed electrodes. Methods. From total lung capacity, subjects performed maximum expiratory pressure (MEP) efforts against a closed airway and voluntary cough efforts. Both efforts were performed with and without superimposed trains of electrical stimulation (50 Hz, 1 second) at a submaximal intensity set to evoke a gastric pressure ( P ga ) of 40 cm H 2 O at functional residual capacity. Results. In the MEP effort, stimulation increased the maximal P ga (from 21.4 ± 7.0 to 59.0 ± 5.7 cm H 2 O) and esophageal pressure ( P es 47.2 ± 11.7 to 65.6 ± 13.6 cm H 2 O). During the cough efforts, stimulation increased P ga (19.5 ± 6.0 to 57.9 ± 7.0 cm H 2 O) and P es (31.2 ± 8.7 to 56.6 ± 10.5 cm H 2 O). The increased expiratory pressures during cough efforts with stimulation increased peak expiratory flow (PEF, by 36% ± 5%), mean expiratory flow (by 80% ± 8%), and expired lung volume (by 41% ± 16%). In every subject, superimposed electrical stimulation improved peak expiratory flow during cough efforts (by 0.99 ± 0.12 L/s range, 0.41-1.80 L/s). Wearing an abdominal binder did not improve stimulated cough flows or pressures. Conclusions. The increases in P ga and PEF with electrical stimulation using the novel posterolateral electrode placement are 2 to 3 times greater than improvements reported in other studies. This suggests that posterolateral electrical stimulation of abdominal muscles is a simple noninvasive way to enhance cough in in iduals with SCI.
Publisher: American Physiological Society
Date: 07-2010
DOI: 10.1152/JAPPLPHYSIOL.01128.2009
Abstract: The reflex mechanism of the short-latency inhibitory reflex to transient loading of human inspiratory muscles is unresolved. Muscle afferents mediate this reflex, but they may act via pontomedullary inspiratory centers, other bulbar networks, or spinal circuits. We hypothesized that altered chemical drive to breathe would alter the initial inhibitory reflex if the neural pathways involve inspiratory medullary centers. Inspiration was transiently loaded in 11 subjects during spontaneous hypercapnic hyperpnea and matched voluntary hyperventilation. Electromyographic activity was recorded bilaterally from scalene muscles with surface electrodes. The latencies of the initial inhibitory response (IR) onset (32 ± 0.7 and 38 ± 1 ms for spontaneous and voluntary conditions respectively, P 0.001) and subsequent excitatory response (ER) onset (80 ± 2.9 and 78 ± 2.6 ms, respectively, P = 0.46) and the normalized sizes of IR (65 ± 2 and 67 ± 3%, respectively, P = 0.50) and ER (51 ± 8 and 69 ± 6%, respectively, P = 0.005) were measured. Mean end-tidal Pco 2 was 43 ± 1.5 Torr with dead space ventilation and was 14 ± 0.6 Torr with matched voluntary hyperventilation ( P 0.001). A mean minute volume liters was achieved in both conditions. The absence of significant difference in the size of the IR suggested that the IR reflex arc does not transit the brain stem inspiratory centers and that the reflex may be integrated at a spinal level. In voluntary hyperventilation, an initial excitation occurred more frequently and, consequently, the IR onset latency was significantly longer. The size of the later ER was also greater during voluntary hyperventilation, which is consistent with it being mediated via longer, presumably cortical, pathways, which are influenced by voluntary drive.
Publisher: Wiley
Date: 18-10-2014
Publisher: Wiley
Date: 11-1993
DOI: 10.1113/JPHYSIOL.1993.SP019908
Abstract: 1. To quantify the net influence of muscle afferent feedback on the firing rates of human motoneurones, the discharge frequencies of single motor axons in the common peroneal nerve were recorded during sustained voluntary efforts performed in the absence of feedback from the target muscle. These data were compared with the firing rates of single motor units in the intact tibialis anterior muscle. In five subjects, recordings were made from fifty-two motor axons innervating tibialis anterior during acute deafferentation and paralysis of the dorsiflexor muscles produced by anaesthetic block of the nerve distal to the recording site. 2. Maximal sustainable firing rates were determined for twenty-four motoneurons, twelve of which were classified as relatively low threshold (estimated recruitment level < or = 10% maximal) and six as high threshold. Mean firing rates of the low-threshold motoneurones (21.7 +/- 2.7 Hz +/- S.E.M.) were significantly higher than those of the high-threshold motoneurones (14.0 +/- 4.4 Hz). The mean firing rate of the twenty-four deafferented motoneurones during maximal efforts to contract the paralysed muscle was 18.6 +/- 1.9 Hz, significantly lower than the maximal firing rates of single motor units recorded from the normally innervated tibialis anterior muscle (28.2 +/- 0.6 Hz). 3. During half-maximal efforts, the mean firing rate of eight deafferented motoneurones (10.8 +/- 1.1 Hz) was significantly lower than that of intact motor units (16.5 +/- 0.2 Hz). A similar finding was apparent during minimal efforts the mean discharge frequency of seven deafferented motoneurones during weak voluntary efforts was 6.0 +/- 0.9 Hz, compared with 7.3 +/- 0.13 Hz for intact motor units. Overall, the range of motoneurone firing rates (from minimal to maximal levels of voluntary effort) was significantly affected by the acute deafferentation, but was shifted significantly to lower rates. 4. During sustained maximal voluntary efforts of at least 30 s duration the firing rate of deafferented motoneurones decreased over the first 5 s but was then maintained, i.e. there was no progressive decline as occurs with normally innervated motor units during fatiguing contractions. This observation supports a reflex origin for the normal decline in motoneurone discharge. 5. It is concluded that muscle afferents in the common peroneal nerve provide a net facilitation to the tibialis anterior motoneurone pool, reflexly increasing the motor output at all levels of voluntary drive by approximately one-third.
Publisher: Oxford University Press (OUP)
Date: 1990
Abstract: The ability to activate human motoneurons supplying in idual intrinsic muscles of the hand was examined during acute deafferentation of the muscles. Tungsten microelectrodes were inserted percutaneously into motor fascicles of the ulnar nerve of 5 subjects, which was then blocked distally with local anaesthetic. In 4 subjects unitary action potentials were recorded from 16 motor axons, which were identified with respect to their target muscles. In the complete absence of muscle afferent feedback, subjects could voluntarily recruit motoneurons, grade their discharge and sustain a constant level of activity. Significant facilitation of motor efforts was provided by cutaneous feedback from the digits via the median nerve. During attempted maximal voluntary efforts the mean discharge frequencies of single motor axons were significantly lower than those of normally-innervated motor units. This finding suggests that peripheral afferents have a net facilitatory influence on motoneurons. However, during prolonged (20-30 s) maximal voluntary efforts the deafferented motoneurons did not display the progressive decline in discharge frequency shown by normally-innervated motor units during contractile fatigue, a finding consistent with two possible explanations: disfacilitation or reflex inhibition of the motoneuron pool by peripheral afferents. The results also indicate that the otherwise intact nervous system can perform some simple motor tasks with no proprioceptive input other than knowledge of the motor commands. Other factors may contribute to the poor motor performance reported for patients with severe sensory deficits.
Publisher: The Company of Biologists
Date: 12-2007
DOI: 10.1242/JEB.002204
Abstract: This study provides the first in vivo measures of the passive length–tension properties of relaxed human muscle fascicles and their tendons. A new method was used to derive passive length–tension properties of human gastrocnemius muscle–tendon units from measures of ankle stiffness obtained at a range of knee angles. Passive length–tension curves of the muscle–tendon unit were then combined with ultrasonographic measures of muscle fascicle length and pennation to determine passive length–tension curves of the muscle fascicles and tendons. Mean slack lengths of the fascicles, tendons and whole muscle–tendon units were 3.3±0.5 cm, 39.5±1.6 cm and 42.3±1.5 cm, respectively (means ± s.d., N=6). On average, the muscle–tendon units were slack (i.e. their passive tension was zero) over the shortest 2.3±1.2 cm of their range. With combined changes of knee and ankle angles, the maximal increase in length of the gastrocnemius muscle–tendon unit above slack length was 6.7±1.9 cm, of which 52.4±11.7% was due to elongation of the tendon. Muscle fascicles and tendons underwent strains of 86.4±26.8% and 9.2±4.1%, respectively, across the physiological range of lengths. We conclude that the relaxed human gastrocnemius muscle–tendon unit falls slack over about one-quarter of its in vivo length and that muscle fascicle strains are much greater than tendon strains. Nonetheless, because the tendons are much longer than the muscle fascicles, tendons contribute more than half of the total compliance of the muscle–tendon unit.
Publisher: American Physiological Society
Date: 03-2022
DOI: 10.1152/JAPPLPHYSIOL.00809.2021
Abstract: Proprioception, which can be defined as the awareness of the mechanical and spatial state of the body and its musculoskeletal parts, is critical to motor actions and contributes to our sense of body ownership. To date, clinical proprioceptive tests have focused on a person’s ability to detect, discriminate, or match limb positions or movements, and reveal that the strength of the relationship between deficits in proprioception and physical function varies widely. Unfortunately, these tests fail to assess higher-level proprioceptive abilities. In this Perspective, we propose that to understand fully the link between proprioception and function, we need to look beyond traditional clinical tests of proprioception. Specifically, we present a novel framework for human proprioception assessment that is ided into two categories: low-level and high-level proprioceptive judgments. Low-level judgments are those made in a single frame of reference and are the types of judgments made in traditional proprioceptive tests (i.e., detect, discriminate or match). High-level proprioceptive abilities involve proprioceptive judgments made in a different frame of reference. For ex le, when a person indicates where their hand is located in space. This framework acknowledges that proprioception is complex and multifaceted and that tests of proprioception should not be viewed as interchangeable, but rather as complimentary. Crucially, it provides structure to the way researchers and clinicians can approach proprioception and its assessment. We hope this Perspective serves as the catalyst for discussion and new lines of investigation.
Publisher: Wiley
Date: 11-1993
DOI: 10.1113/JPHYSIOL.1993.SP019907
Abstract: 1. The study was designed to determine the degree to which normal subjects can control motoneurones innervating a leg muscle when acutely deprived of muscle afferent feedback. Microneurographic recordings were made from eighteen motor fascicles in the common peroneal nerve, of which thirteen innervated tibialis anterior and five toe dorsiflexor muscles. The nerve was then blocked completely at a distal site near the fibular head with local anaesthetic. A sequence of tests was performed with each fascicle to determine the degree to which the subject could control the motoneuronal drive to the paralysed muscle. 2. During a complete distal block of the common peroneal nerve, motoneurones innervating tibialis anterior were frequently activated during weak attempted contraction of the synergist toe extensors and vice versa. 3. When subjects attempted contractions of the paralysed muscles at a constant effort, pressure applied to the dorsum of the foot caused relatively small changes in the level of neural output, producing a small increase in motoneuronal drive to tibialis anterior, but no consistent change in the drive to toe extensor fascicles. 4. Subjects were able to increase the motoneuronal drive to the paralysed tibialis anterior in five steps of effort each lasting 10 s. The level of motor output increased linearly with step number, but declined as the step was maintained, more so when auditory feedback was withdrawn. 5. There was hysteresis in the relationship between motoneuronal output and force (measured on the contralateral side) during attempts to make slowly increasing then decreasing r s of effort on both sides over 20-120 s. Motor drive to the paralysed muscle increased disproportionately rapidly compared with contralateral force when subjects attempted bilaterally symmetrical increasing efforts. 6. Subjects attempted to activate the paralysed muscle group maximally for 20-30 s with auditory feedback of the neurogram and verbal encouragement. There was a small statistically significant reduction in the motoneuronal output 5-10 s into the 30 s effort but, with further encouragement, it recovered towards the end of the effort. 7. When compared directly in the same recording sequences, attempts to make rapid brief maximal efforts (2-3 s duration) produced the same motoneuronal output as attempts to make sustained efforts. 8. Similar results occurred when the motoneuronal output to tibialis anterior was recorded during a selective distal block of tibialis anterior sparing toe dorsiflexors.(ABSTRACT TRUNCATED AT 400 WORDS)
Publisher: Elsevier BV
Date: 06-2016
DOI: 10.1016/J.RESP.2015.05.012
Abstract: During quiet breathing, activation of obligatory inspiratory muscles differs in timing and magnitude. To test the hypothesis that this coordinated activation can be modified, we determined the effect of the upside-down posture compared with standing and lying supine. Subjects (n=14) breathed through a pneumotachometer with calibrated inductance bands around the chest wall and abdomen. Surface electromyographic activity (EMG) was recorded from the scalene muscles. Crural diaphragmatic EMG and oesophageal and gastric pressures were measured in a subset of six subjects. Quiet breathing and standard lung function manoeuvres were performed. The upside-down posture reduced end-expiratory lung volume. During quiet breathing, for the same inspiratory airflow and tidal volume, ribcage contribution decreased, abdominal contribution increased and transdiaphragmatic pressure swing doubled in the upside-down posture compared to standing (p<0.05). Despite this, crural diaphragm EMG was unchanged, whereas scalene muscle EMG was reduced by ∼half (p<0.05). Thus, the mechanical effect of an upside-down posture differentially affects inspiratory muscle activation.
Publisher: Elsevier BV
Date: 09-2015
DOI: 10.1016/J.RESP.2015.05.013
Abstract: There is evidence that psychological factors contribute to the perception of increased difficulty of breathing in patients with chronic obstructive pulmonary disease (COPD), and increase morbidity. We tested the hypothesis that cognitive behaviour therapy (CBT) decreases ratings of perceived dyspnoea in response to resistive loading in patients with COPD. From 31 patients with COPD, 18 were randomised to four sessions of specifically targeted CBT and 13 to routine care. Prior to randomisation, participants were tested with an inspiratory external resistive load protocol (loads between 5 and 45cmH2O/L/s). Six months later, we re-measured perceived dyspnoea in response to the same inspiratory resistive loads and compared results to measurements prior to randomisation. There was a significant 17% reduction in dyspnoea ratings across the loads for the CBT group, and no reduction for the routine care group. The decrease in ratings of dyspnoea suggests that CBT to alleviate breathing discomfort may have a role in the routine treatment of people with COPD.
Publisher: Elsevier BV
Date: 09-2015
DOI: 10.1016/J.RESP.2015.05.010
Abstract: Transcranial magnetic stimulation (TMS) during voluntary muscle contraction causes a period of reduced electromyographic (EMG) activity (EMG). This is attributed to cortical inhibition and is known as the 'silent period'. Silent periods were compared in inspiratory muscles following TMS during voluntary inspiratory efforts during normocapnia, hypercapnia, and hypocapnia. TMS was delivered during isometric and dynamic contractions of scalenes and parasternal intercostals at 25% maximum inspiratory pressure. Changing end-tidal CO2 did not affect the duration of the silent period nor suppression of EMG activity during the silent period. In scalenes, silent periods were shorter for dynamic compared to isometric contractions (p<0.05) but contraction type did not alter the degree of suppression of EMG during the silent period. In parasternal intercostal, no significant differences in silent period parameters occurred for the different contraction types. The lack of effect of end-tidal CO2 suggests that descending drive from the medullary respiratory centres does not independently activate the inspiratory muscles during voluntary inspiratory efforts.
Publisher: Springer Science and Business Media LLC
Date: 07-04-2009
DOI: 10.1007/S00221-009-1780-Y
Abstract: We report an aftereffect in perception of the extent (or degree or range) of joint movement, showing for the first time that a prolonged exposure to a passive back-and-forth movement of a certain extent results in a change in judgment of the extent of a subsequently presented movement. The adapting stimulus, movement about the wrist, had an extent of either 30 degrees or 75 degrees , while the test stimulus was a 50 degrees movement. Following a 4-min adaptation period, the estimated magnitudes of the test stimuli were 61 degrees and 36 degrees in the 30 degrees and 75 degrees condition, respectively (t test(6) = 9.6 p < 0.001). The observed effect is an instance of repulsion or contrast commonly described in perception literature, with perceived value of the test stimulus pushed away from the adapting stimulus.
Publisher: American Physiological Society
Date: 15-02-2014
DOI: 10.1152/JAPPLPHYSIOL.01166.2013
Abstract: With fatiguing exercise, firing of group III/IV muscle afferents reduces voluntary activation and force of the exercised muscles. These afferents can also act across agonist/antagonist pairs, reducing voluntary activation and force in nonfatigued muscles. We hypothesized that maintained firing of group III/IV muscle afferents after a fatiguing adductor pollicis (AP) contraction would decrease voluntary activation and force of AP and ipsilateral elbow flexors. In two experiments ( n = 10) we examined voluntary activation of AP and elbow flexors by measuring changes in superimposed twitches evoked by ulnar nerve stimulation and transcranial magnetic stimulation of the motor cortex, respectively. Inflation of a sphygmomanometer cuff after a 2-min AP maximal voluntary contraction (MVC) blocked circulation of the hand for 2 min and maintained firing of group III/IV muscle afferents. After a 2-min AP MVC, maximal AP voluntary activation was lower with than without ischemia (56.2 ± 17.7% vs. 76.3 ± 14.6% mean ± SD P 0.05) as was force (40.3 ± 12.8% vs. 57.1 ± 13.8% peak MVC P 0.05). Likewise, after a 2-min AP MVC, elbow flexion voluntary activation was lower with than without ischemia (88.3 ± 7.5% vs. 93.6 ± 3.9% P 0.05) as was torque (80.2 ± 4.6% vs. 86.6 ± 1.0% peak MVC P 0.05). Pain during ischemia was reported as Moderate to Very Strong. Postfatigue firing of group III/IV muscle afferents from the hand decreased voluntary drive and force of AP. Moreover, this effect decreased voluntary drive and torque of proximal unfatigued muscles, the elbow flexors. Fatigue-sensitive group III/IV muscle nociceptors act to limit voluntary drive not only to fatigued muscles but also to unfatigued muscles within the same limb.
Publisher: Elsevier BV
Date: 08-2008
DOI: 10.1016/J.RESP.2008.07.007
Abstract: Loading of inspiratory muscles produces a profound short-latency inhibitory response (IR) of the electromyogram (EMG), followed by an excitatory response (ER). Duration of IR correlates positively with the apnoea hypopnoea index in obstructive sleep apnoea (OSA) patients, for whom measurement of this reflex may allow the assessment of a physiological response to therapy. To test the reliability of reflex measurement, we studied 11 human subjects on 4 separate days. Inspiration was transiently occluded during 2 sets of 30 trials on each day. Scalene muscle EMG was rectified and averaged. Ten parameters (4 latencies and 6 EMG sizes) were measured. Reproducibility was analysed by ANOVA, intraclass correlation coefficient (ICC) and coefficient of variation (CV). The mean ICC was 0.56 (range 0.30-0.76) and the mean CV was 25% (range 6.7-48%). These results show good measurement reliability. The abnormalities seen in disease are significantly larger than these CVs. The reflex response to airway occlusion may be assessed reliably using our method.
Publisher: Elsevier BV
Date: 07-2012
DOI: 10.1016/J.CLINPH.2011.11.034
Abstract: The cortical silent period refers to a period of near silence in the electromyogram (EMG) after transcranial magnetic stimulation (TMS) of the motor cortex during contraction. However, low-level EMG of unknown origin is often present. We hypothesised that it arises through spinal reflexes. Sudden lengthening of the muscle as force drops during the silent period could excite muscle spindles and facilitate motoneurones. Subjects (n = 8) performed maximal isometric, shortening and lengthening contractions of the elbow flexors during which TMS (90-100% output) was delivered over the motor cortex. The rate of flexion during shortening contractions reduced muscle lengthening caused by muscle relaxation. Surface EMG was recorded from biceps brachii and brachioradialis, and the low-level EMG during silent periods produced by TMS was measured. Low-level EMG activity was reduced on average by 68% in biceps and 63% in brachioradialis in the shortening contraction compared to all other contraction conditions (p < 0.001). Levels of pre-stimulus EMG were similar between conditions. Muscle lengthening contributes to low-level EMG activity in the silent period, through spinal reflex facilitation by muscle spindle afferents. The silent period depth is not only dependent on cortical output but also reflex effects evoked by muscle lengthening.
Publisher: Wiley
Date: 10-2002
DOI: 10.1113/JPHYSIOL.2002.024539
Abstract: In healthy human subjects, descending motor pathways including the corticospinal tract were stimulated electrically at the level of the cervicomedullary junction to determine the effects on the discharge of motoneurones innervating the biceps brachii. Post-stimulus time histograms (PSTHs) were constructed for 15 single motor units following electrical stimulation of the corticospinal tract and for 11 units following electrical stimulation of large diameter afferents at the brachial plexus. Responses were assessed during weak voluntary contraction. Both types of stimulation produced a single peak at short latency in the PSTH (mean 8.5 and 8.7 ms, respectively) and of short duration (< 1.4 ms). In separate studies, we compared the latency of the responses to electrical stimulation of the corticospinal tract in the relaxed muscle with that in the contracting muscle. The latency was the same in the two conditions when the intensity of the stimulation was adjusted so that responses of the same size could be compared. Estimates of the descending conduction velocity and measurements of presumed peripheral conduction time suggest that there is less than 0.5 ms for spinal events (including synaptic delays). We propose that in response to electrical stimulation of the descending tract fibres, biceps motoneurones receive a large excitatory input with minimal dispersion and it presumably contains a dominant monosynaptic component.
Publisher: Oxford University Press (OUP)
Date: 06-10-2010
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 2016
Publisher: Wiley
Date: 08-11-2013
Publisher: American Physiological Society
Date: 07-0007
DOI: 10.1152/JAPPLPHYSIOL.01053.2007
Abstract: Magnetic and electrical stimulation at different levels of the neuraxis show that supraspinal and spinal factors limit force production in maximal isometric efforts (“central fatigue”). In sustained maximal contractions, motoneurons become less responsive to synaptic input and descending drive becomes suboptimal. Exercise-induced activity in group III and IV muscle afferents acts supraspinally to limit motor cortical output but does not alter motor cortical responses to transcranial magnetic stimulation. “Central” and “peripheral” fatigue develop more slowly during submaximal exercise. In sustained submaximal contractions, central fatigue occurs in brief maximal efforts even with a weak ongoing contraction ( % maximum). The presence of central fatigue when much of the available motor pathway is not engaged suggests that afferent inputs contribute to reduce voluntary activation. Small-diameter muscle afferents are likely to be activated by local activity even in sustained weak contractions. During such contractions, it is difficult to measure central fatigue, which is best demonstrated in maximal efforts. To show central fatigue in submaximal contractions, changes in motor unit firing and force output need to be characterized simultaneously. Increasing central drive recruits new motor units, but the way this occurs is likely to depend on properties of the motoneurons and the inputs they receive in the task. It is unclear whether such factors impair force production for a set level of descending drive and thus represent central fatigue. The best indication that central fatigue is important during submaximal tasks is the disproportionate increase in subjects' perceived effort when maintaining a low target force.
Publisher: American Physiological Society
Date: 12-2021
DOI: 10.1152/JAPPLPHYSIOL.00085.2021
Abstract: This study evaluated upper airway muscle function, breathing, and comfort across different HFNC flows and temperatures. There were no increases in genioglossus muscle activity at higher flows despite greater negative epiglottic pressure swings. Increasing negative pressure swings was associated with increasing discomfort in the nonheated mode. HFNC was associated with ∼7 cmH 2 O increase in positive airway pressure, which may be the primary mechanism for upper airway stability with HFNC rather than increases in pharyngeal muscle activity.
Publisher: Wiley
Date: 14-11-2007
Publisher: Springer Science and Business Media LLC
Date: 22-08-2006
DOI: 10.1007/S00221-006-0570-Z
Abstract: During strong voluntary contractions, activity is not restricted to the target muscles. Other muscles, including contralateral muscles, often contract. We used transcranial magnetic stimulation (TMS) to analyse the origin of these unintended contralateral contractions (termed "associated" contractions). Subjects (n = 9) performed maximal voluntary contractions (MVCs) with their right elbow-flexor muscles followed by submaximal contractions with their left elbow flexors. Electromyographic activity (EMG) during the submaximal contractions was matched to the associated EMG in the left biceps brachii during the right MVC. During contractions, TMS was delivered to the motor cortex of the right or left hemisphere and excitatory motor evoked potentials (MEPs) and inhibitory (silent period) responses recorded from left biceps. Changes at a spinal level were investigated using cervicomedullary stimulation to activate corticospinal paths (n = 5). Stimulation of the right hemisphere produced silent periods of comparable duration in associated and voluntary contractions (218 vs 217 ms, respectively), whereas left hemisphere stimulation caused a depression of EMG but no EMG silence in either contraction. Despite matched EMG, MEPs elicited by right hemisphere stimulation were approximately 1.5-2.5 times larger during associated compared to voluntary contractions (P < 0.005). Similar inhibition of the associated and matched voluntary activity during the silent period suggests that associated activity comes from the contralateral hemisphere and that motor areas in this (right) hemisphere are activated concomitantly with the motor areas in the left hemisphere. Comparison of the MEPs and subcortically evoked potentials implies that cortical excitability was greater in associated contractions than in the matched voluntary efforts.
Publisher: American Physiological Society
Date: 15-02-2015
DOI: 10.1152/JAPPLPHYSIOL.00375.2014
Abstract: During fatiguing upper limb exercise, maintained firing of group III/IV muscle afferents can limit voluntary drive to muscles within the same limb. It is not known if this effect occurs in the lower limb. We investigated the effects of group III/IV muscle afferent firing from fatigued ipsilateral and contralateral extensor muscles and ipsilateral flexor muscles of the knee on voluntary activation of the knee extensors. In three experiments, we examined voluntary activation of the knee extensors by measuring changes in superimposed twitches evoked by femoral nerve stimulation. Subjects attended on 2 days for each experiment. On one day a sphygmomanometer cuff occluded blood flow of the fatigued muscles to maintain firing of group III/IV muscle afferents. After a 2-min extensor contraction ( experiment 1 n = 9), mean voluntary activation was lower with than without maintained ischemia (47 ± 19% vs. 87 ± 8%, respectively P 0.001). After a 2-min knee flexor maximal voluntary contraction (MVC) ( experiment 2 n = 8), mean voluntary activation was also lower with than without ischemia (59 ± 21% vs. 79 ± 9% P 0.01). After the contralateral (left) MVC ( experiment 3 n = 8), mean voluntary activation of the right leg was similar with or without ischemia (92 ± 6% vs. 93 ± 4% P = 0.65). After fatiguing exercise, activity in group III/IV muscle afferents reduces voluntary activation of the fatigued muscle and nonfatigued antagonist muscles in the same leg. However, group III/IV muscle afferents from the fatigued left leg had no effect on the unfatigued right leg. This suggests that any “crossover” of central fatigue in the lower limbs is not mediated by group III/IV muscle afferents.
Publisher: Wiley
Date: 15-01-2020
DOI: 10.1113/JP278433
Publisher: Wiley
Date: 15-01-2015
Publisher: SAGE Publications
Date: 24-07-2013
Abstract: Background. Respiratory complications in people with high-level spinal cord injury (SCI) are a major cause of morbidity and mortality, particularly because of a reduced ability to cough as a result of abdominal muscle paralysis. Objective. We investigated the effect of cough training combined with functional electrical stimulation (FES) over the abdominal muscles for 6 weeks to observe whether training could improve cough strength. Methods. Fifteen SCI subjects (C4-T5) trained for 6 weeks, 5 days per week (5 sets of 10 coughs per day) in a randomized crossover design study. Subjects coughed voluntarily at the same time as a train of electrical stimulation was delivered over the abdominal muscles via posterolaterally positioned electrodes (50 Hz, 3 seconds). Measurements were made of esophageal (P es ) and gastric (P ga ) expiratory pressures and the peak expiratory flow (PEF cough ) produced at the 3 time points of before, during, and after the training. Results. During voluntary coughs, FES cough stimulation improved P ga , P es , and PEF cough acutely, 20-fold, 4-fold, and 50%, respectively. Six weeks of cough training significantly increased P ga (37.1 ± 2.0 to 46.5 ± 2.9 cm H 2 O), P es (35.4 ± 2.7 to 48.1 ± 2.9 cm H 2 O), and PEF cough (3.1 ± 0.1 to 3.6 ± 0.1 L/s). Cough training also improved pressures and flow during voluntary unstimulated coughs. Conclusions. FES of abdominal muscles acutely increases mechanical output in coughing in high-level SCI subjects. Six weeks of cough training further increases gastric and esophageal cough pressures and expiratory cough flow during stimulated cough maneuvers.
Publisher: Springer Science and Business Media LLC
Date: 07-2003
DOI: 10.1007/S00221-003-1457-X
Abstract: Many studies have identified changes in trunk muscle recruitment in clinical low back pain (LBP). However, due to the heterogeneity of the LBP population these changes have been variable and it has been impossible to identify a cause-effect relationship. Several studies have identified a consistent change in the feedforward postural response of transversus abdominis (TrA), the deepest abdominal muscle, in association with arm movements in chronic LBP. This study aimed to determine whether the feedforward recruitment of the trunk muscles in a postural task could be altered by acute experimentally induced LBP. Electromyographic (EMG) recordings of the abdominal and paraspinal muscles were made during arm movements in a control trial, following the injection of isotonic (non-painful) and hypertonic (painful) saline into the longissimus muscle at L4, and during a 1-h follow-up. Movements included rapid arm flexion in response to a light and repetitive arm flexion-extension. Temporal and spatial EMG parameters were measured. The onset and litude of EMG of most muscles was changed in a variable manner during the period of experimentally induced pain. However, across movement trials and subjects the activation of TrA was consistently reduced in litude or delayed. Analyses in the time and frequency domain were used to confirm these findings. The results suggest that acute experimentally induced pain may affect feedforward postural activity of the trunk muscles. Although the response was variable, pain produced differential changes in the motor control of the trunk muscles, with consistent impairment of TrA activity.
Publisher: American Physiological Society
Date: 15-01-2015
Publisher: Elsevier BV
Date: 12-2006
DOI: 10.1016/J.CLINPH.2006.08.008
Abstract: The excitability of the human motor cortex projecting to hand muscles can be reduced by theta burst transcranial magnetic repetitive stimulation (TBS). This study compared the magnitude and variability of changes evoked by TBS for a distal and proximal arm muscle. Eight subjects participated in three studies. In each study, electromyographic responses (MEPs) to single-pulse transcranial magnetic stimulation assessed cortical excitability before and after 40s of TBS. In the first two studies, TBS (intensity, 80% active motor threshold) was delivered to the optimal locations for biceps or first dorsal interosseous (FDI). In the final study, weaker intensity TBS was delivered over the biceps representation. TBS targeting biceps produced highly variable results among subjects. For the group, MEPs were not significantly depressed. Repeat studies in in idual subjects highlighted the variability of responses. For FDI, MEPs were significantly depressed 5min after TBS and remained depressed for >30min (p<0.05). No significant changes in biceps MEPs occurred with weaker TBS. The magnitude and reliability of TBS depends on the region of the cortex targeted. Results obtained for the hand should not be considered indicative of changes that will occur in other regions of the motor cortex or the brain.
Publisher: Elsevier BV
Date: 08-1989
DOI: 10.1016/0034-5687(89)90007-8
Abstract: Low-threshold afferents from human limb muscles are known to project to the sensorimotor cortex and to contribute to proprioception. However, there are few data on the cortical projection of afferents from human respiratory muscles. The present study employed evoked-potential techniques to determine whether low-threshold muscle afferents from the chest wall project to cortical levels in conscious human subjects. In four subjects intramuscular afferents of the second parasternal and fifth lateral intercostal muscles were selectively stimulated through an insulated microelectrode inserted percutaneously at the respective motor point. Evoked potentials were recorded and averaged from eight scalp sites. The initial cortical component of the cerebral response to intramuscular stimulation of the second and fifth interspaces was a negative potential commencing at 19.2 +/- 2.1 msec and 20.7 +/- 1.1 msec respectively. The dominant early cortical potential was largest at the vertex, and was comparable in litude (0.58 +/- 0.23 microV) to that for in idual muscles of the upper and lower limbs. The cortical focus was distributed differently from that for cutaneous afferents of the chest wall and for both muscle and cutaneous afferents from the upper and lower limbs. This study provides direct evidence for a short-latency projection from intercostal muscle afferents (group I and/or II) to the human cerebral cortex.
Publisher: Cambridge University Press (CUP)
Date: 23-12-2002
DOI: 10.1017/S0033291702006839
Abstract: Background. The efficacy and safety of bilateral prefrontal repetitive transcranial magnetic stimulation (rTMS) for treating resistant major depression were examined in a double-blind, placebo-controlled study. Method. Nineteen medication-resistant depressed subjects were randomly assigned to 3 weeks of active or sham rTMS. Effects on mood and neuropsychological function were assessed. Results. Both groups improved significantly in mood over the 3 weeks, but there was no significant difference between active and sham treatments. There were no significant neuropsychological effects. Conclusions. Bilateral rTMS was not superior to sham in treating resistant depression in this pilot study, but caused no neuropsychological impairment.
Publisher: American Physiological Society
Date: 2006
DOI: 10.1152/JAPPLPHYSIOL.00588.2005
Abstract: A maximal inspiratory breath hold (inspiratory capacity apnea) against a closed glottis evokes a large and sustained increase in muscle sympathetic nerve activity (MSNA). Because of its dependence on a high intrathoracic pressure, it has been suggested that this maneuver causes unloading of the low-pressure baroreceptors, known to increase MSNA. To determine the central origins of this sympathoexcitation, we used functional magnetic resonance imaging to define the loci and time course of activation of different brain areas. We hypothesized that, as previously shown for the Valsalvsa maneuver, discrete but widespread regions of the brain would be involved. In 15 healthy human subjects, a series of 90 gradient echo echo-planar image sets was collected during three consecutive 40-s inspiratory capacity apneas using a 3-T scanner. Global signal intensity changes were calculated and subsequently removed by using a detrending technique, which eliminates the global signal component from each voxel's signal intensity change. Whole brain correlations between changes in signal intensity and the known pattern of MSNA during the maneuver were performed on a voxel-by-voxel basis, and significant changes were determined by using a random-effects analysis procedure ( P 0.01, uncorrected). Significant signal increases emerged in multiple areas, including the rostral lateral medulla, cerebellar nuclei, anterior insula, dorsomedial hypothalamus, anterior cingulate, and lateral prefrontal cortexes. Decreases in signal intensity occurred in the dorsomedial and caudal lateral medulla, cerebellar cortex, hippoc us, and posterior cingulate cortex. Given that many of these sites have roles in cardiovascular control, the sustained increase in MSNA during an inspiratory capacity apnea is likely to originate from a distributed set of discrete areas.
Publisher: Public Library of Science (PLoS)
Date: 26-04-2017
Publisher: Wiley
Date: 02-2006
Publisher: SAGE Publications
Date: 28-04-2015
Abstract: Stepping impairments increase fall risk in people with MS. No studies have evaluated step training for reducing fall risk in this population. To determine if step training can improve physical and neuropsychological measures associated with falls in MS. 50 PwMS with moderate disability participated in a randomized controlled trial in which intervention group participants ( n = 28) performed step training for 12 weeks while controls ( n = 22) continued usual physical activity. The primary outcomes were choice stepping reaction time (CSRT) and Stroop stepping test (SST) time. Secondary outcomes included balance test (postural sway, CSRT components), gait speed and cognitive tests, nine-hole peg test (9-HPT) and MS functional composite (MSFC) score. 44 participants completed the study and no adverse events were reported. Compared with the control group, the intervention group performed significantly better at retest in CSRT and SST times, and tests of sway with eyes open, 9-HPT, single and dual task gait speed and MSFC score. There was a non-significant trend for fewer falls in the intervention group. The findings indicate that the step training programme is feasible, safe and effective in improving stepping, standing balance, coordination and functional performance in people with MS.
Publisher: Wiley
Date: 24-04-2016
DOI: 10.1113/JP272164
Publisher: American Physiological Society
Date: 09-2014
DOI: 10.1152/JAPPLPHYSIOL.01257.2013
Abstract: Upper airway muscles are important in maintaining airway patency. Visualization of their dynamic motion should allow measurement, comparison, and further understanding of their roles in healthy subjects and those with upper airway disorders. Currently, there are few clinically feasible real-time imaging methods. Methods such as tagged magnetic resonance imaging have documented movement of genioglossus (GG), the largest upper airway dilator. Inspiratory movement was largest in the posterior region of GG. This study aimed to develop a novel ultrasound (US) method to measure GG movement in real time. We tested 20 healthy, awake subjects (21–38 yr) breathing quietly in the supine posture with the head in a neutral position. US images were collected using a transducer positioned submentally. Image correlation analysis measured regional displacement of GG within a grid of points in the midsagittal plane throughout the respiratory cycle. Typically, motion began before inspiratory flow in an anteroinferior direction and peaked in midinspiration. Average peak displacements of the anterior, posterior, superior, and inferior grid points were 0.44 ± 0.23 (mean ± SD), 0.57 ± 0.35, 0.38 ± 0.20, and 0.62 ± 0.41 mm, respectively. Largest displacements occurred in the most inferoposterior part (0.70 ± 0.48 mm). This method had good intrarater repeatability within the same testing session, as well as across sessions. We have devised a simple noninvasive US method, which should be a useful tool to assess GG movement in normal subjects and those with sleep-disordered breathing.
Publisher: American Physiological Society
Date: 07-2021
DOI: 10.1152/JAPPLPHYSIOL.00017.2021
Abstract: A potent short-latency reflex inhibition of inspiratory muscles produced by airway occlusion was tested in people with COPD and age-matched controls. The reflex was more prevalent in COPD, presumably due to an increased neural drive to breathe. When present, the reflex was similar in duration in the two groups, longer than historical data for younger control groups. The work reveals novel differences in reflex control of inspiratory muscles due to aging as well as COPD.
Publisher: European Respiratory Society
Date: 09-2016
Publisher: American Physiological Society
Date: 04-2017
DOI: 10.1152/JAPPLPHYSIOL.00976.2016
Abstract: There are few comprehensive investigations of the changes in muscle architecture that accompany muscle contraction or change in muscle length in vivo. For this study, we measured changes in the three-dimensional architecture of the human medial gastrocnemius at the whole muscle level, the fascicle level and the fiber level using anatomical MRI and diffusion tensor imaging (DTI). Data were obtained from eight subjects under relaxed conditions at three muscle lengths. At the whole muscle level, a 5.1% increase in muscle belly length resulted in a reduction in both muscle width (mean change −2.5%) and depth (−4.8%). At the fascicle level, muscle architecture measurements obtained at 3,000 locations per muscle showed that for every millimeter increase in muscle-tendon length above the slack length, average fascicle length increased by 0.46 mm, pennation angle decreased by 0.27° (0.17° in the superficial part and 0.37° in the deep part), and fascicle curvature decreased by 0.18 m −1 . There was no evidence of systematic variation in architecture along the muscle’s long axis at any muscle length. At the fiber level, analysis of the diffusion signal showed that passive lengthening of the muscle increased diffusion along fibers and decreased diffusion across fibers. Using these measurements across scales, we show that the complex shape changes that muscle fibers, whole muscles, and aponeuroses of the medial gastrocnemius undergo in vivo cannot be captured by simple geometrical models. This justifies the need for more complex models that link microstructural changes in muscle fibers to macroscopic changes in architecture. NEW & NOTEWORTHY Novel MRI and DTI techniques revealed changes in three-dimensional architecture of the human medial gastrocnemius during passive lengthening. Whole muscle belly width and depth decreased when the muscle lengthened. Fascicle length, pennation, and curvature changed uniformly or near uniformly along the muscle during passive lengthening. Diffusion of water molecules in muscle changes in the same direction as fascicle strains.
Publisher: Elsevier BV
Date: 05-2016
DOI: 10.1016/J.JBIOMECH.2016.02.014
Abstract: The length and pennation of muscle fascicles are frequently measured using ultrasonography. Conventional ultrasonography imaging methods only provide two-dimensional images of muscles, but muscles have complex three-dimensional arrangements. The most accurate measurements will be obtained when the ultrasound transducer is oriented so that endpoints of a fascicle lie on the ultrasound image plane and the image plane is oriented perpendicular to the aponeurosis, but little is known about how to find this optimal transducer orientation in the frequently-studied medial gastrocnemius muscle. In the current study, we determined the optimal transducer orientation at 9 sites in the medial gastrocnemius muscle of 8 human subjects by calculating the angle of misalignment between three-dimensional muscle fascicles, reconstructed from diffusion tensor images, and the plane of a virtual ultrasound image. The misalignment angle was calculated for a range of tilts and rotations of the ultrasound transducer relative to a reference orientation that was perpendicular to the skin and parallel to the tibia. With the transducer in the reference orientation, the misalignment was substantial (mean across sites and subjects of 6.5°, range 1.4 to 20.2°). However for all sites and subjects a near-optimal alignment (on average 2.6°, range 0.5° to 6.0°) could be achieved by maintaining 0° tilt and applying a small rotation (typically less than 10°). On the basis of these data we recommend that ultrasonographic measurements of medial gastrocnemius muscle fascicle architecture be obtained, at least for relaxed muscles under static conditions, with the transducer oriented perpendicular to the skin and nearly parallel to the tibia.
Publisher: Wiley
Date: 29-02-2008
Publisher: Wiley
Date: 17-06-2013
Publisher: American Physiological Society
Date: 15-05-2015
Publisher: Elsevier
Date: 2003
Publisher: Wiley
Date: 08-1991
DOI: 10.1113/JPHYSIOL.1991.SP018721
Abstract: 1. To address whether the muscle spindle support to alpha-motoneurones is maintained during prolonged isometric voluntary contractions, the discharge of eighteen muscle spindle afferents, originating in the dorsiflexors of the ankle or toes, was recorded from the common peroneal nerve in eight subjects. Isometric contractions were generally sustained for 1 min, usually below 30% of the maximal voluntary dorsiflexion force. 2. Once the afferent had been identified, subjects were instructed to dorsiflex the foot slowly to recruit the spindle ending, to continue the r contraction until a predetermined target force was reached, and then to hold that force until requested to relax. 3. Five muscle spindle afferents maintained a constant discharge frequency during the hold phase of the isometric contraction. Following relaxation of the contraction two spindle afferents from tibialis anterior, exhibited a post-contraction discharge despite the absence of detectable electromyographic activity (EMG). 4. The discharge frequency of most of the spindle afferents (72%) declined progressively during the isometric contraction. The mean firing rates had declined to two-thirds of those at the onset of the contraction by 30 s, and to half after 1 min. The decline in spindle firing rate commenced during the r phase of the contraction and was statistically significant by 10 s, when force was held constant. The extent of the decline was greater for those units with the higher initial firing rates and for those units studied after many preceding contractions. 5. In the same contractions a progressive increase in EMG was required to maintain force and consequently the change in EMG was inversely related to the change in spindle discharge. While many mechanisms may contribute to the decline in spindle discharge during a sustained isometric contraction, it is argued that the result will be a progressive disfacilitation of alpha-motoneurones, which may contribute to the decline in motor unit firing rates during a sustained contraction.
Publisher: Elsevier BV
Date: 06-2005
DOI: 10.1016/J.JBIOMECH.2004.05.046
Abstract: The study of muscle growth and muscle length adaptations requires measurement of passive length-tension properties of in idual muscles, but until now such measurements have only been made in animal muscles. We describe a new method for measuring passive length-tension properties of human gastrocnemius muscles in vivo. Passive ankle torque and ankle angle data were obtained as the ankle was rotated through its full range with the knee in a range of positions. To extract gastrocnemius passive length-tension curves from passive torque-angle data it was assumed that passive ankle torque was the sum of torque due to structures which crossed only the ankle joint (this torque was a 6-parameter function of ankle joint angle) and a torque due to the gastrocnemius muscle (a 3-parameter function of knee and ankle angle). Parameter values were estimated with non-linear regression and used to reconstruct passive length-tension curves of the gastrocnemius. The reliability of the method was examined in 11 subjects by comparing three sets of measurements: two on the same day and the other at least a week later. Length-tension curves were reproducible: the average root mean square error was 5.1+/-1.1 N for pairs of measurements taken within a day and 7.3+/-1.2 N for pairs of measurements taken at least a week apart (about 3% and 6% of maximal passive tension, respectively). Length-tension curves were sensitive to mis-specification of moment arms, but changes in length-tension curves were not. The new method enables reliable measurement of passive length-tension properties of human gastrocnemius in vivo, and is likely to be useful for investigation of changes in length-tension curves over time.
Publisher: Wiley
Date: 15-07-2011
Publisher: Wiley
Date: 11-07-2016
DOI: 10.1002/MUS.25217
Abstract: The maximal compound muscle action potential (Mmax ) of biceps brachii is altered by 1 session of strength training. We examined whether the number of training sets in a session plays a role in this effect. Ten subjects completed 1 session of isometric strength training of the elbow flexors (2 sets, 75% maximal force with 1 arm 12 sets with the other). Biceps Mmax was acquired in both arms before training, immediately after training, and every 5 min for 30 min. Mmax area was initially potentiated after 2 (7.2%) and 12 sets (13.6%) but returned to baseline within 5 min. Biceps Mmax is similarly affected by 2 and 12 sets of strength training. The overall effect is minimal compared with ∼25% depression reported after similar training in a different arm posture. Thus, changes in Mmax appear more dependent on training posture than number of training sets. Muscle Nerve 54: 791-793, 2016.
Publisher: Wiley
Date: 08-2002
DOI: 10.1113/JPHYSIOL.2002.023861
Abstract: In humans, the flexor digitorum profundus (FDP), which is a multi-tendoned muscle, produces forces that flex the four distal interphalangeal joints of the fingers. We determined whether the force associated with activity in a single motor unit in the FDP was confined to a single finger or distributed to more than one finger during a natural grasp. The discharge of single low-threshold motor units (n = 69) was recorded at sites across the muscle during weak voluntary grasping involving all fingers and spike-triggered averaging of the forces under each of the finger pads was used to assess the distribution pattern. Spike-triggered averaging revealed that time-locked changes in force occurred under the 'test' finger (that finger on which the unit principally acted) as well as under the 'non-test' fingers. However, for the index-, middle- and ring-finger units, the changes in force under non-test fingers were typically small ( 50 % of those under the test finger). The distribution of forces by little-finger units differed significantly from that for each of the other three fingers. Apart from increases in force under non-test fingers, there was occasional unloading of adjacent fingers (22/267 combinations), usually affecting the index finger. The increases in force under the test finger correlated significantly with the background force for units acting on the middle, ring and little fingers. During a functional grasp, the activity of single units in the FDP allows for a relatively selective control of forces at the tips of the index, middle and ring fingers, but this is limited for little-finger units.
Publisher: Wiley
Date: 03-2003
Publisher: American Physiological Society
Date: 2011
DOI: 10.1152/JAPPLPHYSIOL.00413.2010
Abstract: The electromyographic (EMG) activity of human upper airway muscles, particularly the genioglossus, has been widely measured, but the relationship between EMG activity and physical movement of the airway muscles remains unclear. We aimed to measure the motion of the soft tissues surrounding the airway during normal and loaded inspiration on the basis of the hypothesis that this motion would be affected by the addition of resistance to breathing during inspiration. Tagged MR imaging of seven healthy subjects was performed in a 3-T scanner. Tagged 8.6-mm-spaced grids were used, and complementary spatial modulation of magnetization images were acquired beginning ∼200 ms before inspiratory airflow. Deformation of tag line intersections was measured. The genioglossus moved anteriorly during normal and loaded inspiration, with less movement during loaded inspiration. The motion of tissues at the anterior border of the upper airway was nonuniform, with larger motions inferiorly. At the level of the soft palate, the lateral dimension of the airway decreased significantly during loaded inspiration (−0.15 ± 0.09 and −0.48 ± 0.09 mm during unloaded and loaded inspiration, respectively, P 0.05). When resistance to inspiratory flow was added, genioglossus motion and lateral dimensions of the airway at the level of the soft palate decreased. Our results suggest that genioglossus motion begins early to dilate the airway prior to airflow and that inspiratory loading reduces the anterior motion of the genioglossus and increases the collapse of the lateral airway walls at the level of the soft palate.
Publisher: Wiley
Date: 14-04-2020
DOI: 10.1113/JP279220
Publisher: American Physiological Society
Date: 05-2007
DOI: 10.1152/JAPPLPHYSIOL.00962.2006
Abstract: Force responses to transcranial magnetic stimulation of motor cortex (TMS) during exercise provide information about voluntary activation and contractile properties of the muscle. Here, TMS-generated twitches and muscle relaxation during the TMS-evoked silent period were measured in fresh, heated, and fatigued muscle. Subjects performed isometric contractions of elbow flexors in two studies. Torque and EMG were recorded from elbow flexor and extensor muscles. One study ( n = 6) measured muscle contraction times and relaxation rates during brief maximal and submaximal contractions in fresh and fatigued muscle. Another study ( n = 7) aimed to 1) assess the reproducibility of muscle contractile properties during brief voluntary contractions in fresh muscle, 2) validate the technique for contractile properties in passively heated muscle, and 3) apply the technique to study contractile properties during sustained maximal voluntary contractions. In both studies, muscle contractile properties during voluntary contractions were compared with the resting twitch evoked by motor nerve stimulation. Measurement of muscle contractile properties during voluntary contractions is reproducible in fresh muscle and reveals faster and slower muscle relaxation rates in heated and fatigued muscle, respectively. The technique is more sensitive to altered muscle state than the traditional motor nerve resting twitch. Use of TMS during sustained maximal contractions reveals slowing of muscle contraction and relaxation with different time courses and a decline in voluntary activation. Voluntary output from the motor cortex becomes insufficient to maintain complete activation of muscle, although slowing of muscle contraction and relaxation indicates that lower motor unit firing rates are required for fusion of force.
Publisher: Wiley
Date: 06-2002
DOI: 10.1113/JPHYSIOL.2002.016782
Abstract: Transcranial magnetic stimulation activates corticospinal neurones directly and transsynaptically and hence, activates motoneurones and results in a response in the muscle. Transmastoid stimulation results in a similar muscle response through activation of axons in the spinal cord. This study was designed to determine whether the two stimuli activate the same descending axons. Responses to transcranial magnetic stimuli paired with electrical transmastoid stimuli were examined in biceps brachii in human subjects. Twelve interstimulus intervals (ISIs) from -6 ms (magnet before transmastoid) to 5 ms were investigated. When responses to the in idual stimuli were set at 10-15 % of the maximal M-wave, responses to the paired stimuli were larger than expected at ISIs of -6 and -5 ms but were reduced in size at ISIs of -2 to 1 ms and at 3 to 5 ms. With in idual responses of 3-5 % of maximal M-wave, facilitation still occurred at ISIs of -6 and -5 ms and depression of the paired response at ISIs of 0, 1, 4 and 5 ms. The interaction of the response to transmastoid stimulation with the multiple descending volleys elicited by magnetic stimulation of the cortex is complex. However, depression of the response to the paired stimuli at short ISIs is consistent with an occlusive interaction in which an antidromic volley evoked by the transmastoid stimulus collides with and annihilates descending action potentials evoked by the transcranial magnetic stimulus. Thus, it is consistent with the two stimuli activating some of the same corticospinal axons.
Publisher: Wiley
Date: 09-2019
DOI: 10.1113/JP278498
Publisher: Wiley
Date: 31-05-2006
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 2009
DOI: 10.1016/J.PAIN.2008.10.007
Abstract: The most obvious impairments associated with spinal cord injury (SCI) are loss of sensation and motor control. However, many subjects with SCI also develop persistent neuropathic pain below the injury which is often severe, debilitating and refractory to treatment. The underlying mechanisms of persistent neuropathic SCI pain remain poorly understood. Reports in utees describing phantom limb pain demonstrate a positive correlation between pain intensity and the amount of primary somatosensory cortex (S1) reorganization. Of note, this S1 reorganization has also been shown to reverse with pain reduction. It is unknown whether a similar association between S1 reorganization and pain intensity exists in subjects with SCI. The aim of this investigation was to determine whether the degree of S1 reorganization following SCI correlated with on-going neuropathic pain intensity. In 20 complete SCI subjects (10 with neuropathic pain, 10 without neuropathic pain) and 21 control subjects without SCI, the somatosensory cortex was mapped using functional magnetic resonance imaging during light brushing of the right little finger, thumb and lip. S1 reorganization was demonstrated in SCI subjects with the little finger activation point moving medially towards the S1 region that would normally innervate the legs. The amount of S1 reorganization in subjects with SCI significantly correlated with on-going pain intensity levels. This study provides evidence of a link between the degree of cortical reorganization and the intensity of persistent neuropathic pain following SCI. Strategies aimed at reversing somatosensory cortical reorganization may have therapeutic potential in central neuropathic pain.
Publisher: Wiley
Date: 29-02-2008
Publisher: Wiley
Date: 14-04-2010
Publisher: Ubiquity Press, Ltd.
Date: 2023
DOI: 10.5334/TOHM.731
Publisher: Elsevier BV
Date: 08-2009
DOI: 10.1016/J.JPAIN.2009.01.327
Abstract: Intramuscular injection of hypertonic saline produces pain in the belly of the injected muscle (primary pain) and, often, pain that projects distally (referred pain). While it is known that referred pain can be induced during complete sensory block of the distal site, there is little evidence as to whether the perception of referred pain depends on ongoing input from the primary stimulus. We assessed whether blocking the noxious input following the induction of pain blocks the primary but not the referred pain. A cannula was inserted into the tibialis anterior muscle in 15 subjects (8 male, 7 female). In a quasi-random crossover design conducted over 2 experimental sessions, each subject received a bolus intramuscular injection of .5 mL of 5% hypertonic saline, followed 90 seconds later by either: A) A second bolus injection or B) An injection of 2 mL lignocaine through the same cannula. Protocol A was followed 60 seconds later by either a sham injection or an injection of lignocaine, while protocol B was followed 60 seconds later by either a sham injection or an injection of hypertonic saline. Subjects mapped the areas of primary and referred pain, and rated the intensities at these sites every 30 seconds until the cessation of pain. In all subjects, the area and intensity of primary pain rapidly disappeared within 7.5 minutes of intramuscular lignocaine injection (P < .02 relative to the nonanesthesia condition). With the exception of 2 subjects, in whom the referred pain continued in the absence of primary pain, the referred pain declined in parallel with local pain: the mean total pain intensity declined by 74% in both regions. We conclude that the maintenance of referred muscle pain usually depends on ongoing noxious inputs from the site of primary muscle pain. Referred pain is a significant clinical problem, and commonly occurs with pain originating in muscle but not from skin. It is important to know the primary source of the pain so that treatment can be directed to this site rather to the site of referral.
Publisher: American Physiological Society
Date: 06-2006
Abstract: This study investigated transmission of corticospinal output through motoneurons over a wide range of voluntary contraction strengths in humans. During voluntary contraction of biceps brachii, motor evoked potentials (MEPs) to transcranial magnetic stimulation of the motor cortex grow up to about 50% maximal force and then decrease. To determine whether the decrease reflects events at a cortical or spinal level, responses to stimulation of the cortex and corticospinal tract (cervicomedullary motor evoked potentials, CMEPs) as well as maximal M-waves (M max ) were recorded during strong contractions at 50 to 100% maximum. In biceps and brachioradialis, MEPs and CMEPs (normalized to M max ) evoked by strong stimuli decreased during strong elbow flexions. Responses were largest during contractions at 75% maximum and both potentials decreased by about 25% M max during maximal efforts ( P 0.001). Reductions were smaller with weaker stimuli, but again similar for MEPs and CMEPs. Thus the reduction in MEPs during strong voluntary contractions can be accounted for by reduced responsiveness of the motoneuron pool to stimulation. During strong contractions of the first dorsal interosseous, a muscle that increases voluntary force largely by frequency modulation, MEPs declined more than in either elbow flexor muscle (35% M max , P 0.001). This suggests that motoneuron firing rates are important determinants of evoked output from the motoneuron pool. However, motor cortical output does not appear to be limited at high contraction strengths.
Publisher: American Physiological Society
Date: 10-2016
DOI: 10.1152/JAPPLPHYSIOL.01000.2015
Abstract: In obstructive sleep apnea (OSA), the short-latency inhibitory reflex (IR) of inspiratory muscles to airway occlusion is prolonged in proportion to the severity of the OSA. The mechanism underlying the prolongation may relate to chronic inspiratory muscle loading due to upper airway obstruction or sensory changes due to chronic OSA-mediated inflammation. Continuous positive airway pressure (CPAP) therapy prevents upper airway obstruction and reverses inflammation. We therefore tested whether CPAP therapy normalized the IR abnormality in OSA. The IR responses of scalene muscles to brief airway occlusion were measured in 37 adult participants with untreated, mostly severe, OSA, of whom 13 were restudied after the initiation of CPAP therapy (usage h/night). Participants received CPAP treatment as standard clinical care, and the mean CPAP usage between initial and subsequent studies was 6.5 h/night (range 4.1-8.8 h/night) for a mean of 19 mo (range 4–41 mo). The duration of the IR in scalene muscles in response to brief (250 ms) inspiratory loading was confirmed to be prolonged in the participants with OSA. The IR was assessed before and after CPAP therapy. CPAP treatment did not normalize the prolonged duration of the IR to airway occlusion (60 ± 21 ms pretreatment vs. 59 ± 18 ms posttreatment, means ± SD) observed in participants with severe OSA. This suggests that the prolongation of IR reflects alterations in the reflex pathway that may be irreversible, or a specific disease trait.
Publisher: Elsevier BV
Date: 05-2013
DOI: 10.1016/J.APMR.2012.10.034
Abstract: To evaluate psychometric properties of 16-item and 7-item Falls Efficacy Scale-International (FES-I) in people with multiple sclerosis (MS). Validation and prospective cohort study. People with MS living in metropolitan areas. Community-dwelling people with MS (N=169 aged 21-73y) who were referred to Multiple Sclerosis Australia for physiotherapy assessment. Not applicable. FES-I scores and a range of sociodemographic, physical, and neuropsychological measures. The mean score for the 16-item FES-I was 34.9±11.2, and the mean score for the 7-item FES-I was 14.7±4.7. FES-I total scores were normally distributed: skewness of .35 (SEM=.19) for the 16-item and .47 (SEM .19) for the 7-item FES-I, indicating the absence of floor and ceiling effects. Internal reliability was excellent, with Cronbach's alpha values of .94 (16-item) and .86 (7-item). Rasch analyses indicated that the structure and measurement properties were better for the 7-item FES-I than for the 16-item FES-I. Construct validity of both scales was supported by sensitivity to group differences relating to demographic characteristics and fall-risk factors. The findings indicate that both 16-item and 7-item versions of the FES-I provide valuable information about the fear of falling in people with MS. However, the 7-item version of FES-I has better psychometric properties in people with MS.
Publisher: Elsevier BV
Date: 2015
DOI: 10.1016/J.RESP.2014.11.017
Abstract: Maximal voluntary protrusion force of the human tongue has not been examined in positions beyond the incisors or at different lung volumes. Tongue force was recorded with the tongue tip at eight positions relative to the incisors (12 and 4mm protrusion, neutral and 4, 12, 16, 24 and 32mm retraction) at functional residual capacity (FRC), total lung capacity (TLC) and residual volume (RV) in 15 healthy subjects. Maximal force occurred between 12mm and 32mm retraction (median 16mm). Maximum force at FRC was reproducible at the optimal tongue position across sessions (P=0.68). Across all positions at FRC the average force was highest at 24mm retraction (28.3±5.3N, mean±95% CI) and lowest at 12mm protrusion (49.1±4.6% maximum P<0.05). Across all tongue positions, maximal force was on average 9.3% lower at FRC than TLC and RV (range: 4.5-12.7% maximum, P<0.05). Retracted positions produce higher-force protrusions with a small effect of lung volume.
Publisher: Springer Science and Business Media LLC
Date: 30-08-2019
Publisher: Wiley
Date: 03-05-2013
DOI: 10.1002/NBM.2964
Abstract: Physiological and pathological changes to the anisotropic mechanical properties of skeletal muscle are still largely unknown, with only a few studies quantifying changes in vivo. This study used the noninvasive MR elastography (MRE) technique, in combination with diffusion tensor imaging (DTI), to measure shear modulus anisotropy in the human skeletal muscle in the lower leg. Shear modulus measurements parallel and perpendicular to the fibre direction were made in 10 healthy subjects in the medial gastrocnemius, soleus and tibialis anterior muscles. The results showed significant differences in the medial gastrocnemius (μ‖ = 0.86 ± 0.15 kPa μ⊥ = 0.66 ± 0.19 kPa, P < 0.001), soleus (μ‖ = 0.83 ± 0.22 kPa μ⊥ = 0.65 ± 0.13 kPa, P < 0.001) and the tibialis anterior (μ‖ = 0.78 ± 0.24 kPa μ⊥ = 0.66 ± 0.16 kPa, P = 0.03) muscles, where the shear modulus measured in the direction parallel is greater than that measured in the direction perpendicular to the muscle fibres. No significant differences were measured across muscle groups. This study provides the first direct estimates of the anisotropic shear modulus in the triceps surae muscle group, and shows that the technique may be useful for the probing of mechanical anisotropy changes caused by disease, aging and injury.
Publisher: Oxford University Press (OUP)
Date: 13-11-2007
Abstract: Noxious stimulation of skeletal muscle evokes pain that is often referred into distal areas. Despite referred pain being of significant clinical importance, the brain regions responsible for the perception of referred pain remain unexplored. The aim of this investigation is to define these regions using functional magnetic resonance imaging. We induced muscle pain by hypertonic saline injections (0.5 ml) into the tibialis anterior (TA) or flexor carpi radialis (FCR) muscle. TA injections evoked pain that was referred to the ankle/foot in 10/17 subjects, whereas FCR injections evoked pain that was projected into the wrist/hand in 6/12 subjects. Regional brain responses were statistically tested by convolving the temporal profile of the subjective pain intensity rating with the hemodynamic response function. For all subjects, signal increased in the region of primary somatosensory cortex (SI), which represents the leg or arm, that is, the area corresponding to the injection site. However, for those subjects who reported referred pain, signal intensity increases also occurred in the SI region representing the foot or hand. Interestingly, differential signal changes also occurred in anterior cingulate, cerebellar, and insular cortices. This is the first study to provide evidence of cortical differentiation in the processing of primary and referred pain.
Publisher: Wiley
Date: 08-10-2020
DOI: 10.1113/JP279458
Abstract: Respiration plays a key role in the circulation of cerebrospinal fluid (CSF) around the central nervous system. During inspiration increased venous return from the cranium is believed to draw CSF rostrally. However, this mechanism does not explain why CSF has also been observed to move caudally during inspiration. We show that during inspiration decreased intrathoracic pressure draws venous blood from the cranium and lumbar spine towards the thorax. We also show that the abdominal pressure was associated with rostral CSF displacement. However, a caudal shift of cervical CSF was seen with low abdominal pressure and comparably negative intrathoracic pressures. These results suggest that the effects of epidural blood flow within the spinal canal need to be considered, as well as the cranial blood volume balance, to understand respiratory‐related CSF flow. These results may prove useful for the treatment of CSF obstructive pathology and understanding the behaviour of intrathecal drug injections. It is accepted that during inspiration, cerebrospinal fluid (CSF) flows rostrally to compensate for decreased cranial blood volume, caused by venous drainage due to negative intrathoracic pressure. However, this mechanism does not explain observations of caudal CSF displacement during inspiration. Determining the drivers of respiratory CSF flow is crucial for understanding the pathophysiology of CSF flow disorders. To quantify the influence of respiration on CSF flow, real‐time phase‐contrast magnetic resonance imaging (MRI) was used to record CSF and blood flow, while healthy subjects (5:5 M:F, 25–50 years) performed either a brief expiratory or inspiratory effort between breaths. Transverse images were taken perpendicular to the spinal canal in the middle of the C3 and L2 vertebrae. The same manoeuvres were then performed after a nasogastric pressure catheter was used to measure the intrathoracic and abdominal pressures. During expiratory‐type manoeuvres that elevated abdominal and intrathoracic pressures, epidural blood flow into the spinal canal increased and CSF was displaced rostrally. With inspiratory manoeuvres, the negative intrathoracic pressure drew venous blood from C3 and L2 towards the thoracic spinal canal, and cervical CSF was displaced both rostrally and caudally, despite the increased venous drainage. Regression analysis showed that rostral displacement of CSF at both C3 (adjusted R 2 = 0.53 P 0.001) and L2 (adjusted R 2 = 0.38 P 0.001) were associated with the abdominal pressure. However, with low abdominal pressure and comparably negative intrathoracic pressure, cervical CSF flowed caudally. These findings suggest that changes in both the cranial and spinal pressures need to be considered to understand respiratory CSF flow.
Publisher: Elsevier BV
Date: 11-2006
DOI: 10.1016/J.CLINPH.2006.07.303
Abstract: To investigate whether a short-duration reduction of input to the motor cortex affects excitability in the hand region of the motor cortex. Subjects (n=10) received sets of transcranial magnetic stimulation of the motor cortex (TMS) and peripheral ulnar nerve stimulation. Stimuli were delivered before and after 20 min of inactivity of the test hand. The evoked compound muscle action potentials were recorded in two relaxed intrinsic hand muscles using surface EMG. Motor evoked potential size (MEP expressed relative to the maximal M-wave) increased by approximately 30-40 in both hand muscles (P=0.012) following inactivity. The enlarged MEP was not associated with changes in F-wave size, a marker of motoneurone excitability, or changes in intracortical inhibition and facilitation measured with paired-pulse TMS. MEP growth most likely reflects an increase in motor cortical excitability. The increased excitability appears to be more associated with reduced voluntary drive to and from the motor cortex rather than reduced afferent input from the periphery. These results have important implications for any investigation of motor cortical excitability in relaxed subjects. The outcome of an experimental intervention is the net result of the intervention itself and alterations in cortical excitability produced by the subjects' inactivity.
Publisher: Elsevier BV
Date: 02-2011
DOI: 10.1016/J.RESP.2010.11.014
Abstract: To assess the cortical contribution to breathing, low-intensity transcranial magnetic stimulation (TMS) was delivered over the motor cortex in 10 subjects during: (i) voluntary static inspiratory efforts, (ii) hypocapnic voluntary ventilation (end-tidal CO(2), 2.7±0.4% mean±SD), and (iii) hypercapnic involuntary ventilation (end-tidal CO(2), 6.0±0.7%). Electromyographic activity (EMG) was recorded from the scalene muscles (obligatory inspiratory muscles) and was significantly suppressed by TMS at short latency (17.2±1.7ms). The scalene EMG was reduced to 76±8% and 76±7% in voluntary breathing and the static inspiratory effort, respectively, but only to 91±10% during the involuntary ventilation, significantly less than during the two voluntary tasks (p<0.005). Thus, with differences in chemical drive to breathe, TMS shows differences in the cortical contribution to inspiratory activity in scalene muscles. Voluntary breathing showed larger suppression than involuntary breathing, when the suppression was marginal. The results strongly suggest that drive from fast-conducting corticospinal neurones contributes to inspiratory activity in scalenes during voluntary breathing but is not required during involuntary breathing.
Publisher: Elsevier BV
Date: 05-1977
DOI: 10.1016/0034-5687(77)90007-X
Abstract: It has been shown previously that there is a reduction in tidal volume in response to longitudinal sternal vibration at 100 Hz. In the present study it was shown that the effect of such vibration is to reduce tidal volume (VT) and prolong inspiratory time (ti) in such a way that points from vibrated and non-vibrated breaths fall on the same VT:ti curve. This indicates that the normal mechanisms which terminate inspiration are unaffected by vibration. The effect of vibration is simply to reduce the rate at which inspiration proceeds. This was illustrated here when vibration reduced the rate of fall of intrapleural pressure during inspiration, and also reduced the instantaneous ventilation at any level of chemical drive. Electrophysiological recordings made here from phrenic motoneurones support these findings. It is concluded that sensory nerves in the chest wall, which can be excited by vibration, can inhibit inspiration.
Publisher: Springer Science and Business Media LLC
Date: 03-05-2014
DOI: 10.1007/S00702-014-1218-Y
Abstract: Abnormal substantia nigra morphology in healthy in iduals, viewed with transcranial ultrasound, is a significant risk factor for Parkinson's disease. However, little is known about the functional consequences of this abnormality (termed 'hyperechogenicity') on movement. The aim of the current study was to investigate hand function in healthy older adults with (SN+) and without (SN-) substantia nigra hyperechogenicity during object manipulation. We hypothesised that SN+ subjects would exhibit increased grip force and a slower rate of force application compared to SN- subjects. Twenty-six healthy older adults (8 SN+ aged 58 ± 8 years, 18 SN- aged 57 ± 6 years) were asked to grip and lift a light-weight object with the dominant hand. Horizontal grip force, vertical lift force, acceleration, and first dorsal interosseus EMG were recorded during three trials. During the first trial, SN+ subjects exhibited a longer period between grip onset and lift onset (i.e. preload duration 0.27 ± 0.25 s) than SN- subjects (0.13 ± 0.08 s P = 0.046). They also exerted a greater downward force prior to lift off (-0.54 ± 0.42 N vs. -0.21 ± 0.12 N P = 0.005) and used a greater grip force to lift the object (19.5 ± 7.0 N vs. 14.0 ± 4.3 N P = 0.022) than SN- subjects. No between group differences were observed in subsequent trials. SN+ subjects exhibit impaired planning for manipulation of new objects. SN+ in iduals over-estimate the grip force required, despite a longer contact period prior to lifting the object. The pattern of impairment observed in SN+ subjects shares similarities with de novo Parkinson's disease patients.
Publisher: Springer Science and Business Media LLC
Date: 19-03-2015
DOI: 10.1007/S00221-015-4249-1
Abstract: The brain needs information about the size of the body to control our interactions with the environment. No receptor signals this information directly the brain must determine body size from multiple sensory inputs and then store this information. This process is poorly understood, but somatosensory information is thought to play a role. In particular, anaesthetising a body part has been reported to make it feel bigger. Here, we report the first study to measure whether changes in body size following anaesthesia are uniform across dimensions (e.g. width and length). We blocked the digital nerves of ten human subjects with a clinical dose of local anaesthetic (1 % lignocaine) and again in separate sessions with a weaker dose (0.25 % lignocaine) and a saline control. Subjects reported the perceived size of their index finger by selecting templates from a set that varied in size and aspect ratio. We also measured changes in sensory signals that might contribute to the anaesthetic-induced changes using quantitative sensory testing. Subjects perceived their finger to be up to 32 % wider during anaesthesia when compared to during a saline control condition. However, changes in perceived length of the finger were much smaller (<5 %). Previous studies have shown a change in perceived body size with anaesthesia, but have assumed that the aspect ratio is preserved. Our data show that this is not the case. We suggest that nonuniform changes in perceived body size might be due to the brain increasing the body's perimeter to protect it from further injury.
Publisher: SAGE Publications
Date: 26-05-2009
Abstract: Objective: To determine whether the addition of electrical stimulation to progressive resistance training increases the voluntary strength of the wrist muscles in people with tetraplegia. Design: Assessor-blind within-subject randomised controlled trial. Setting: Two Australian spinal cord injury units and the community. Participants: Sixty-four wrists of 32 people with tetraplegia and bilateral weakness of the wrist extensor or flexor muscles (grade 2 - 4 Medical Research Council grades). Interventions: Participants' wrists were randomly allocated to one of two conditions. Wrist muscles of the experimental arm received electrical stimulation superimposed on progressive resistance training. The wrist muscles of the contralateral arm received sham electrical stimulation superimposed on progressive resistance training. Both arms received 6 sets of 10 contractions three times a week for eight weeks such that the only difference between arms was the application of electrical stimulation. Main Measures: The primary outcome was maximal voluntary isometric strength. Secondary outcomes were a fatigue resistance ratio representing voluntary and electrically-stimulated endurance. Measurements were taken at the start and end of the eight-week treatment period. Results: The mean treatment effect (95% Confidence Interval) of electrical stimulation for voluntary strength was 0.04 Nm (95% CI, -0.5 to 0.6 p =0.89). The mean treatment effect (95% CI) for fatigue ratio representing voluntary endurance and electrically-stimulated endurance was -0.01 (95% CI, -0.1 to 0.1 p =0.78) and -0.07 (95% CI, -0.3 to 0.1 p =0.47), respectively. Conclusions: Voluntary strength of the wrist is not enhanced by the addition of electrical stimulation to progressive resistance training programs in people with tetraplegia.
Publisher: Elsevier BV
Date: 10-2003
DOI: 10.1016/S1569-9048(03)00161-7
Abstract: In animals, high-intensity unilateral stimulation of the phrenic nerve results in short-latency inhibition of phrenic and intercostal nerve activity bilaterally. This study provides the first demonstration in human subjects of a short-latency inhibitory response in the contralateral scalene, parasternal intercostal and diaphragm muscles to single stimuli delivered at cervical level to the phrenic nerve. Electromyographic (EMG) responses were recorded with intramuscular and surface electrodes. An inhibitory response with an onset latency of approximately 35 ms followed by a long-latency excitatory response at approximately 100 ms were observed in the three inspiratory muscles. The inhibition was evident in single trials, averaged EMG, histograms of the discharge of single motor units, and even when the phrenic nerve stimulus intensity was relatively low. Thus, the inhibition may be mediated by large-diameter muscle afferents. The latency of this potent inhibitory response to contralateral phrenic nerve stimulation is too long to be mediated via a simple spinal circuit and may involve a brainstem projection.
Publisher: Elsevier BV
Date: 03-2010
DOI: 10.1016/J.JBIOMECH.2009.11.017
Abstract: Comprehensive characterization of stress relaxation in musculotendinous structures is needed to create robust models of viscoelastic behavior. The commonly used quasi-linear viscoelastic (QLV) theory requires that the relaxation response be independent of tissue strain (length). This study aims to characterize stress relaxation in the musculotendinous and ligamentous structures crossing the human ankle (ankle-only structures and the gastrocnemius muscle-tendon unit, which crosses the ankle and knee), and to determine whether stress relaxation is independent of the length of these structures. Two experiments were conducted on 8 healthy subjects. The first experiment compared stress relaxation over 10 min at different gastrocnemius muscle-tendon unit lengths keeping the length of ankle-joint only structures fixed. The second experiment compared stress relaxation at different lengths of ankle-joint only structures keeping gastrocnemius muscle-tendon unit length fixed. Stress relaxation data were fitted with a two-term exponential function (T=G(0)+G(1)e(-lambda(1))(t)+G(2)e(-lambda(2))(t)). The first experiment demonstrated a significant effect of gastrocnemius muscle-tendon unit length on G(1), and the second experiment demonstrated an effect of the length of ankle-joint only structures on G(2), lambda(1) and lambda(2) (p<0.05). Nonetheless, the size of effects on stress relaxation was small (DeltaG/G<10%), similar to experimental variability. We conclude that stress relaxation in the relaxed human ankle is minimally affected by changing gastrocnemius muscle-tendon unit length or by changing the lengths of ankle-joint only structures. Consequently quasi-linear viscoelastic models of the relaxed human ankle can use a common stress relaxation modulus at different knee and ankle angles with minimal error.
Publisher: Wiley
Date: 21-03-2007
Publisher: Wiley
Date: 15-12-2015
Publisher: Elsevier BV
Date: 04-2001
DOI: 10.1016/S0006-3223(00)00996-3
Abstract: The safety of repetitive transcranial magnetic stimulation (rTMS) has only previously been formally studied in volunteers receiving a single session of stimulation or in a small number of depressed subjects receiving a 2-week treatment course. This study examined safety issues in depressed subjects receiving up to 4 weeks of rTMS. Efficacy results from this study have been previously reported. Eighteen subjects with DSM-IV major depression participated in a 2-week, parallel, double-blind, sham-controlled study of rTMS treatment. Twelve subjects then went on to receive 4 weeks active rTMS in an open follow-up. We examined the effects of rTMS on neuropsychologic function (up to 4 weeks), auditory threshold (up to 6 weeks exposure to rTMS noise), and an electroencephalogram (after 2 weeks). Data were analyzed by repeated measures analysis. There were trends for improvement in neuropsychologic performance, probably due to practice effects. No mean changes in auditory threshold occurred, but two patients showed mild high-frequency hearing loss after several weeks of rTMS. Electroencephalograms in two patients, one of whom had sham stimulation, showed minor abnormality. No significant mean deficits were demonstrated in this cohort. Overall, rTMS for up to 4 weeks is safe, but in idual results suggest caution and the need for further investigation of the safety of several weeks of rTMS.
Publisher: Society for Neuroscience
Date: 03-05-2006
DOI: 10.1523/JNEUROSCI.5487-05.2006
Abstract: The role of group III and IV muscle afferents in controlling the output from human muscles is poorly understood. We investigated the effects of these afferents from homonymous or antagonist muscles on motoneuron pools innervating extensor and flexor muscles of the elbow. In study 1, subjects ( n = 8) performed brief maximal voluntary contractions (MVCs) of elbow extensors before and after a 2 min MVC of the extensors. During MVCs, electromyographic responses from triceps were evoked by stimulation of the corticospinal tracts [cervicomedullary motor evoked potentials (CMEPs)]. The same subjects repeated the protocol, but input from fatigue-sensitive afferents was prolonged after the fatiguing contraction by maintained muscle ischemia. In study 2, CMEPs were evoked in triceps during brief extensor MVCs before and after a 2 min sustained flexor MVC ( n = 7) or in biceps during brief flexor MVCs before and after a sustained extensor MVC ( n = 7). Again, ischemia was maintained after the sustained contractions. During sustained MVCs of the extensors, CMEPs in triceps decreased by ∼35%. Without muscle ischemia, CMEPs recovered within 15 s, but with maintained ischemia, they remained depressed (by ∼28% p 0.001). CMEPs in triceps were also depressed (by ∼20% p 0.001) after fatiguing flexor contractions, whereas CMEPs in biceps were facilitated (by ∼25% p 0.001) after fatiguing extensor contractions. During fatigue, inputs from group III and IV muscle afferents from homonymous or antagonist muscles depress extensor motoneurons but facilitate flexor motoneurons. The more pronounced inhibitory influence of these afferents on extensors suggests that these muscles may require greater cortical drive to generate force during fatigue.
Publisher: Wiley
Date: 31-10-2016
DOI: 10.1113/EP085753
Publisher: American Physiological Society
Date: 11-2005
DOI: 10.1152/JAPPLPHYSIOL.00559.2005
Abstract: Evidence that unilateral training increases contralateral strength is inconsistent, possibly because existing studies have design limitations such as lack of control groups, lack of randomization, and insufficient statistical power. This study sought to determine whether unilateral resistance training increases contralateral strength. Subjects ( n = 115) were randomly assigned to a control group or one of the following four training groups that performed supervised elbow flexion contractions: 1) one set at high speed, 2) one set at low speed, 3) three sets at high speed, or 4) three sets at low speed. Training was 3 times/wk for 6 wk with a six- to eight-repetition maximum load. Control subjects attended sessions but did not exercise. Elbow flexor strength was measured with a one-repetition maximum arm curl before and after training. Training with one set at slow speed did not produce an increase in contralateral strength (mean effect of −1% or −0.07 kg 95% confidence interval: −0.42–0.28 kg P = 0.68). However, three sets increased strength of the untrained arm by a mean of 7% of initial strength (additional mean effect of 0.41 kg 95% confidence interval: 0.06–0.75 kg P = 0.022). There was a tendency for training with fast contractions to produce a greater increase in contralateral strength than slow training (additional mean effect of 5% or 0.31 kg 95% confidence interval: −0.03–0.66 kg P = 0.08), but there was no interaction between the number of sets and training speed. We conclude that three sets of unilateral resistance exercise produce small contralateral increases in strength.
Publisher: Elsevier BV
Date: 10-2011
DOI: 10.1016/J.RESP.2011.06.010
Abstract: In this review, we consider the discharge of human respiratory motoneurones during involuntary and voluntary contractions and what this reveals about the neural control of respiratory muscles. Motoneurone discharge is the final output of neural drive and can be recorded in humans during a range of experimental protocols. However, human studies have limitations and recordings can only be made indirectly from motoneurones. Animal data allows us to hypothesise how neural drive to these motoneurones is organised in humans. We propose that premotoneuronal networks, perhaps in the spinal cord (i.e. 'spinal distribution networks'), sculpt descending drive from multiple sources. This would determine the differential pattern of activation across inspiratory muscles, preserve the neural and mechanical coupling when voluntary breaths are taken and allow for different patterns of activation in non-respiratory contractions.
Publisher: Springer Science and Business Media LLC
Date: 11-07-2009
DOI: 10.1007/S00221-009-1921-3
Abstract: Stimuli that preferentially activate rapidly adapting cutaneous receptors impair proprioception in the fingers. These experiments assessed potential mechanisms. The ability to detect passive movements about interphalangeal joints of the fingers was measured when vibrotactile stimuli were applied to the moving digit or to an adjacent digit at a high frequency (300 Hz) and low litude (50 microm peak-to-peak) that favours activation of Pacinian corpuscle (PC) afferents. Detection of movement was significantly impaired when vibration was applied to either digit. However, vibration applied to an anaesthetized adjacent digit caused no impairment. Impairment of proprioception was still observed when only skin and joint (but not muscle) afferents could contribute to detection, but was not significant with only muscle afferents intact during anaesthesia of the moving digit. We suggest that activation of PC afferents, either in or near the moving digit, impairs movement detection through an interaction predominantly between the classes of cutaneous afferents.
Publisher: Elsevier BV
Date: 09-2005
DOI: 10.1016/J.JBIOMECH.2004.08.016
Abstract: Intra-abdominal pressure (IAP) increases during many tasks and has been argued to increase stability and stiffness of the spine. Although several studies have shown a relationship between the IAP increase and spinal stability, it has been impossible to determine whether this augmentation of mechanical support for the spine is due to the increase in IAP or the abdominal muscle activity which contributes to it. The present study determined whether spinal stiffness increased when IAP increased without concurrent activity of the abdominal and back extensor muscles. A sustained increase in IAP was evoked by tetanic stimulation of the phrenic nerves either unilaterally or bilaterally at 20 Hz (for 5 s) via percutaneous electrodes in three subjects. Spinal stiffness was measured as the force required to displace an indentor over the L4 or L2 spinous process with the subjects lying prone. Stiffness was measured as the slope of the regression line fitted to the linear region of the force-displacement curve. Tetanic stimulation of the diaphragm increased IAP by 27-61% of a maximal voluntary pressure increase and increased the stiffness of the spine by 8-31% of resting levels. The increase in spinal stiffness was positively correlated with the size of the IAP increase. IAP increased stiffness at L2 and L4 level. The results of this study provide evidence that the stiffness of the lumbar spine is increased when IAP is elevated.
Publisher: Elsevier BV
Date: 04-2011
DOI: 10.1016/J.JBIOMECH.2011.01.005
Abstract: Several studies have measured the elastic properties of a single human muscle-tendon unit in vivo. However the viscoelastic behavior of single human muscles has not been characterized. In this study, we adapted QLV theory to model the viscoelastic behavior of human gastrocnemius muscle-tendon units in vivo. We also determined the influence of viscoelasticity on passive length-tension properties of human gastrocnemius muscle-tendon units. Eight subjects participated in the experiment, which consisted of two parts. First, the stress relaxation response of human gastrocnemius muscle-tendon units was determined at a range of knee and ankle angles. Subsequently, passive ankle torque and ankle angle were collected during cyclic dorsiflexion and plantarflexion at a range of knee angles. Viscous parameters were determined by fitting the stress relaxation experiment data with a two-term exponential function, and elastic parameters were estimated by fitting the QLV model and viscous parameters to the cyclic experiment data. The model fitted the experimental data well at slow speeds (RMSE: 1.7 ± 0.5N) and at fast speeds (RMSE: 1.9 ± 0.2N). Muscle-tendon units demonstrated a large amount of stress relaxation. Nonetheless, viscoelastic passive length-tension curves estimated with the QLV model were similar to elastic passive length-tension curves obtained using a model that ignored viscosity. There was little difference in the elastic passive length-tension curves at different loading rates. We conclude that (a) the QLV model can be used to quantify viscoelastic behaviors of relaxed human gastrocnemius muscle-tendon units in vivo, and (b) over the range of velocities we examined, the velocity of loading has little effect on the passive length-tension properties of human gastrocnemius muscle-tendon units.
Publisher: Wiley
Date: 07-11-2022
DOI: 10.1113/JP283703
Abstract: Profiling performance in the physiological domains underpinning upper limb function (such as strength, sensation, coordination) provides insight into an in idual's specific impairments. This compliments the traditional medical ‘diagnosis’ model that is currently used in contemporary medicine. From an initial battery of 13 tests in which data were collected across the adult lifespan ( n = 367, 20–95 years) and in those with neurological conditions (specifically, multiple sclerosis ( n = 40), Parkinson's disease ( n = 34), and stroke ( n = 50)), six tests were selected to comprise a core upper limb physiological profile assessment (PPA). This comprised measures of handgrip strength, simple reaction time, finger dexterity, tactile sensation, bimanual coordination, and a functional task. In idual performance in each of these tests can be compared to a reference population score (devised from our database of healthy in iduals aged under 60 years), informing the researcher or clinician how to best direct an intervention or treatment for the in idual based on their specific impairment(s). Lastly, a composite score calculated from the average performance across the six tests provides a broad overview of an in idual's overall upper limb function. Collectively, the upper limb PPA highlights specific impairments that are prevalent within distinct pathologies and reveals the magnitude of upper limb motor impairment specific to each condition. image
Publisher: Elsevier BV
Date: 04-2015
DOI: 10.1016/J.JBIOMECH.2015.01.012
Abstract: In vivo measurements of muscle architecture provide insight into inter-in idual differences in muscle function and could be used to personalise musculoskeletal models. When muscle architecture is measured from ultrasound images, as is frequently done, it is assumed that fascicles are oriented in the image plane and, for some measurements, that the image plane is perpendicular to the aponeurosis at the intersection of fascicle and aponeurosis. This study presents an in vivo validation of these assumptions by comparing ultrasound image plane orientation to three-dimensional reconstructions of muscle fascicles and aponeuroses obtained with diffusion tensor imaging (DTI) and high-resolution anatomical MRI scans. It was found that muscle fascicles were oriented on average at 5.5±4.1° to the ultrasound image plane. On average, ultrasound yielded similar measurements of fascicle lengths to DTI (difference <3mm), suggesting that the measurements were unbiased. The absolute difference in length between any pair of measurements made with ultrasound and DTI was substantial (10mm or 20% of the mean), indicating that the measurements were imprecise. Pennation angles measured with ultrasound were significantly smaller than those measured with DTI (mean difference 6°). This difference was apparent only at the superficial insertion of the muscle fascicles so it was probably due to pressure on the skin applied by the ultrasound probes. It is concluded that ultrasound measurements of deep pennation angles and fascicle lengths in the medial gastrocnemius are unbiased but have a low precision and that superficial pennation angles are underestimated by approximately 10°. The low precision limits the use of ultrasound to personalise fascicle length in musculoskeletal models.
Publisher: American Physiological Society
Date: 04-2020
Abstract: A tongue muscle, the genioglossus (GG), is important in maintaining pharyngeal airway patency. Previous recordings of multiunit electromyogram (EMG) suggest it is activated during inspiration in humans with some tonic activity in expiration. We recorded from populations of single motor units in GG in seven subjects during quiet breathing when awake. Ultrasonography assisted electrode placement. The activity of single units was separated into six classes based on a step-wise analysis of the discharge pattern. Phasic and tonic activities were analyzed statistically with the coefficient of determination ( r 2 ) between discharge frequency and lung volume. Of the 110 motor units, 29% discharged tonically without phasic respiratory modulation (firing rate ∼19 Hz). Further, 16% of units increased their discharge during expiration (expiratory phasic and expiratory tonic units). Only half the units increased their discharge during inspiration (inspiratory phasic and inspiratory tonic units). Units firing tonically with an inspiratory increase had significantly higher discharge rates than those units that only fired phasically (peak rates 25 vs. 16 Hz, respectively). Simultaneous recordings of two or three motor units showed neighboring units with differing respiratory and tonic drives. Our results provide a classification and the first quantitative measures of human GG motor-unit behavior and suggest this activity results from a complex interaction of inspiratory, expiratory, and tonic drives at the hypoglossal motor nucleus. The presence of different drives to GG implies that complex premotor networks can differentially engage human hypoglossal motoneurons during respiration. This is unlike the ordered recruitment of motor units in limb and axial muscles.
Publisher: American Physiological Society
Date: 07-2009
Abstract: It is difficult to test responses of human motoneurons in a controlled way or to make longitudinal assessments of adaptive changes at the motoneuron level. These studies assessed the reliability of responses produced by magnetic stimulation of the corticospinal tract. Cervicomedullary motor evoked potentials (CMEPs) were recorded in the first dorsal interosseus (FDI) on 2 separate days. On each day, four sets of stimuli were delivered at the maximal output of the stimulator, with the final two sets ≥10 min after the initial sets. Sets of stimuli were also delivered at different stimulus intensities to obtain stimulus-response curves. In addition, on the second day, responses at different stimulus intensities were evoked during weak voluntary contractions. Responses were normalized to the maximal muscle compound action potential ( M max ). CMEPs evoked in the relaxed FDI were small, even when stimulus intensity was maximal (3.6 ± 2.5% M max ) but much larger during a weak contraction (e.g., 26.2 ± 10.2% M max ). CMEPs evoked in the relaxed muscle at the maximal output of the stimulator were highly reproducible both within (ICC = 0.83, session 1 ICC = 0.87, session 2) and between sessions (ICC = 0.87). ICCs for parameters of the input-output curves, which included measures of motor threshold, slope, and maximal response size, ranged between 0.87 and 0.62. These results suggest that responses to magnetic stimulation of the corticospinal tract can be assessed in relaxation and contraction and can be reliably obtained for longitudinal studies of motoneuronal excitability.
Publisher: American Physiological Society
Date: 09-2011
DOI: 10.1152/JAPPLPHYSIOL.00603.2011
Abstract: Muscle pain has widespread effects on motor performance, but the effect of pain on voluntary activation, which is the level of neural drive to contracting muscle, is not known. To determine whether induced muscle pain reduces voluntary activation during maximal voluntary contractions, voluntary activation of elbow flexors was assessed with both motor-point stimulation and transcranial magnetic stimulation over the motor cortex. In addition, we performed a psychophysical experiment to investigate the effect of induced muscle pain across a wide range of submaximal efforts (5–75% maximum). In all studies, elbow flexion torque was recorded before, during, and after experimental muscle pain by injection of 1 ml of 5% hypertonic saline into biceps. Injection of hypertonic saline evoked deep pain in the muscle (pain rating ∼5 on a scale from 0 to 10). Experimental muscle pain caused a small (∼5%) but significant reduction of maximal voluntary torque in the motor-point and motor cortical studies ( P 0.001 and P = 0.045, respectively n = 7). By contrast, experimental muscle pain had no significant effect on voluntary activation when assessed with motor-point and motor cortical stimulation although voluntary activation tested with motor-point stimulation was reduced by ∼2% in contractions after pain had resolved ( P = 0.003). Furthermore, induced muscle pain had no significant effect on torque output during submaximal efforts ( P 0.05 n = 6), which suggests that muscle pain did not alter the relationship between the sense of effort and production of voluntary torque. Hence, the present study suggests that transient experimental muscle pain in biceps brachii has a limited effect on central motor pathways.
Publisher: Wiley
Date: 28-09-2007
Publisher: American Thoracic Society
Date: 15-11-2005
Publisher: American Physiological Society
Date: 04-2007
DOI: 10.1152/JAPPLPHYSIOL.00865.2006
Abstract: Abdominal muscles are the most important expiratory muscles for coughing. Spinal cord-injured patients have respiratory complications because of abdominal muscle weakness and paralysis and impaired ability to cough. We aimed to determine the optimal positioning of stimulating electrodes on the trunk for the noninvasive electrical activation of the abdominal muscles. In six healthy subjects, we compared twitch pressures produced by a single electrical pulse through surface electrodes placed either posterolaterally or anteriorly on the trunk with twitch pressures produced by magnetic stimulation of nerve roots at the T 10 level. A gastroesophageal catheter measured gastric pressure (Pga) and esophageal pressure (Pes). Twitches were recorded at increasing stimulus intensities at functional residual capacity (FRC) in the seated posture. The maximal intensity used was also delivered at total lung capacity (TLC). At FRC, twitch pressures were greatest with electrical stimulation posterolaterally and magnetic stimulation at T 10 and smallest at the anterior site (Pga, 30 ± 3 and 33 ± 6 cmH 2 O vs. 12 ± 3 cmH 2 O Pes 8 ± 2 and 11 ± 3 cmH 2 O vs. 5 ± 1 cmH 2 O means ± SE). At TLC, twitch pressures were larger. The values for posterolateral electrical stimulation were comparable to those evoked by thoracic magnetic stimulation. The posterolateral stimulation site is the optimal site for generating gastric and esophageal twitch pressures with electrical stimulation.
Publisher: Wiley
Date: 29-07-2018
DOI: 10.1113/JP275764
Publisher: Informa UK Limited
Date: 28-05-2012
DOI: 10.3109/17482968.2012.673169
Abstract: Respiratory pacing has advanced the long-term management of respiratory failure secondary to neurological disorders. It has an established role in curtailing invasive mechanical ventilation after upper motor neuron lesions such as spinal cord injury. There is increasing interest to expand the application of intramuscular diaphragm pacing to amyotrophic lateral sclerosis (ALS), a progressive and fatal neurodegenerative disease. Although diaphragm pacing has been offered to ALS patients, evidence-based data to determine its benefits remain lacking. The limited current literature indicates progression of respiratory dysfunction in ALS patients despite diaphragm pacing. The data from clinical trials are inadequate to substantiate its survival and sleep benefits. Its advantages over non-invasive mechanical ventilation have not been directly investigated. Furthermore, there are cautions for ALS patients to consider when opting for diaphragm pacing. Progressive degeneration of the phrenic motor neurons in classic ALS will interrupt the transmission of pacer signals to sustain diaphragm contractions. Pacing protocols that are safe for other neurological conditions may be detrimental for ALS, at least as suggested by transgenic animal models. Issues inherent to the device warrant expert intervention in implanted patients. At present, clinical effectiveness and long-term safety concerns about diaphragm pacing in ALS remain to be addressed.
Publisher: Wiley
Date: 25-04-2018
DOI: 10.1113/JP275527
Publisher: Oxford University Press (OUP)
Date: 30-04-2008
Publisher: American Physiological Society
Date: 03-2011
Publisher: Wiley
Date: 09-2015
DOI: 10.1113/JP270902
Abstract: Intramuscular electrodes developed over the past 80 years can record the concurrent activity of only a few motor units active during a muscle contraction. We designed, produced and tested a novel multi‐channel intramuscular wire electrode that allows in vivo concurrent recordings of a substantially greater number of motor units than with conventional methods. The electrode has been extensively tested in deep and superficial human muscles. The performed tests indicate the applicability of the proposed technology in a variety of conditions. The electrode represents an important novel technology that opens new avenues in the study of the neural control of muscles in humans. We describe the design, fabrication and testing of a novel multi‐channel thin‐film electrode for detection of the output of motoneurones in vivo and in humans, through muscle signals. The structure includes a linear array of 16 detection sites that can s le intramuscular electromyographic activity from the entire muscle cross‐section. The structure was tested in two superficial muscles (the abductor digiti minimi (ADM) and the tibialis anterior (TA)) and a deep muscle (the genioglossus (GG)) during contractions at various forces. Moreover, surface electromyogram (EMG) signals were concurrently detected from the TA muscle with a grid of 64 electrodes. Surface and intramuscular signals were decomposed into the constituent motor unit (MU) action potential trains. With the intramuscular electrode, up to 31 MUs were identified from the ADM muscle during an isometric contraction at 15% of the maximal force (MVC) and 50 MUs were identified for a 30% MVC contraction of TA. The new electrode detects different sources from a surface EMG system, as only one MU spike train was found to be common in the decomposition of the intramuscular and surface signals acquired from the TA. The system also allowed access to the GG muscle, which cannot be analysed with surface EMG, with successful identification of MU activity. With respect to classic detection systems, the presented thin‐film structure enables recording from large populations of active MUs of deep and superficial muscles and thus can provide a faithful representation of the neural drive sent to a muscle.
Publisher: American Physiological Society
Date: 04-2004
DOI: 10.1152/JAPPLPHYSIOL.01116.2003
Abstract: Spinal tracts can be stimulated noninvasively in human subjects by passing a high-voltage stimulus between the mastoids or by magnetic stimulation over the back of the head. The stimulus probably activates the corticospinal tract at the cervicomedullary junction (pyramidal decussation) and evokes large, short-latency motor responses in the arm muscles. These responses have a large monosynaptic component. Responses in leg muscles can be elicited by cervicomedullary junction stimulation or by stimulation over the cervical or thoracic spine. Because nerve roots are more easily activated than spinal tracts, stimulus spread to motor axons can occur. Facilitation of responses by voluntary activity confirms that the responses are evoked synaptically. Stimulation of the corticospinal tract is useful in studies of central conduction and studies of the behavior of motoneurons during different tasks. It also provides an important comparison to allow interpretation of changes in responses to stimulation of the motor cortex. The major drawback to the use of electrical stimulation of the corticospinal tract is that each stimulus is transiently painful.
Publisher: American Physiological Society
Date: 04-2016
Abstract: Biceps brachii motor evoked potentials (MEPs) from cortical stimulation are influenced by arm posture. We used subcortical stimulation of corticospinal axons to determine whether this postural effect is spinal in origin. While seated at rest, 12 subjects assumed several static arm postures, which varied in upper-arm (shoulder flexed, shoulder abducted, arm hanging to side) and forearm orientation (pronated, neutral, supinated). Transcranial magnetic stimulation over the contralateral motor cortex elicited MEPs in resting biceps and triceps brachii, and electrical stimulation of corticospinal tract axons at the cervicomedullary junction elicited cervicomedullary motor evoked potentials (CMEPs). MEPs and CMEPs were normalized to the maximal compound muscle action potential (M max ). Responses in biceps were influenced by upper-arm and forearm orientation. For upper-arm orientation, biceps CMEPs were 68% smaller ( P = 0.001), and biceps MEPs 31% smaller ( P = 0.012), with the arm hanging to the side compared with when the shoulder was flexed. For forearm orientation, both biceps CMEPs and MEPs were 34% smaller (both P 0.046) in pronation compared with supination. Responses in triceps were influenced by upper-arm, but not forearm, orientation. Triceps CMEPs were 46% smaller ( P = 0.007) with the arm hanging to the side compared with when the shoulder was flexed. Triceps MEPs and biceps and triceps MEP/CMEP ratios were unaffected by arm posture. The novel finding is that arm posture-dependent changes in corticospinal excitability in humans are largely spinal in origin. An interplay of multiple reflex inputs to motoneurons likely explains the results.
Publisher: American Physiological Society
Date: 05-2012
Abstract: Short periods of training in motor tasks can increase motor cortical excitability. This study investigated whether changes also occur at a subcortical level. Subjects trained in ballistic finger abduction or visuomotor tracking. The right index finger rotated around the metacarpophalangeal (MCP) joint in a splint. Surface EMG was recorded from the first dorsal interosseous. Transcranial magnetic stimulation over the back of the head (double-cone coil) elicited cervicomedullary motor evoked potentials (CMEPs) by stimulation of corticospinal axons. Responses were recorded from the relaxed muscle before, between, and after two sets of training. In study 1 ( n = 7), training comprised two sets of 150 maximal finger abductions. Feedback of acceleration was provided. With training, acceleration increased significantly. CMEPs increased to 248 ± 152% (± SD) of baseline immediately after training ( P = 0.007) but returned to control level (155 ± 141%) 10 min later. In study 2 ( n = 7), subjects matched MCP joint angle to a target path on a computer screen. After ∼30 min of training, tracking improved as shown by increased correlation between joint angle and the target pathway, reduced time lag, and reduced EMG rms . However, CMEPs remained unchanged. These results show that transmission through the corticospinal pathway at a spinal level increased after repeated ballistic movements but not after training in a visuomotor task. Thus, changes at a spinal level may contribute to improved performance in some motor tasks.
Publisher: Elsevier BV
Date: 02-2011
DOI: 10.1016/J.JBIOMECH.2010.09.027
Abstract: Biomechanical properties of the human tongue are needed for finite element models of the upper airway and may be important to elucidate the pathophysiology of obstructive sleep apneoa. Tongue viscoelastic properties have not been characterized previously. Magnetic resonance elastography (MRE) is an emerging imaging technique that can measure the viscoelastic properties of soft tissues in-vivo. In this study, MRE was used to measure the viscoelastic properties of the tongue and soft palate in 7 healthy volunteers during quiet breathing. Results show that the storage shear modulus of the tongue and soft palate is 2.67±0.29 and 2.53±0.31 kPa (mean ± SD), respectively. This is the first study to investigate the mechanical properties of the tongue using MRE, and it provides necessary data for future studies of patient groups with altered upper airway function.
Publisher: Wiley
Date: 05-03-2010
DOI: 10.1111/J.1748-1716.2009.02066.X
Abstract: This review considers the operation of the corticospinal system in primates. There is a relatively widespread cortical area containing corticospinal outputs to a single muscle and thus a motoneurone pool receives corticospinal input from a wide region of the cortex. In addition, corticospinal cells themselves have ergent intraspinal branches which innervate more than one motoneuronal pool but the synergistic couplings involving the many hand muscles are likely to be more erse than can be accommodated simply by fixed patterns of corticospinal ergence. Many studies using transcranial magnetic stimulation of the human motor cortex have highlighted the capacity of the cortex to modify its apparent excitability in response to altered afferent inputs, training and various pathologies. Studies using cortical stimulation at 'very low' intensities which elicit only short-latency suppression of the discharge of motor units have revealed that the rapidly conducting corticospinal axons (stimulated at higher intensities) drive motoneurones in normal voluntary contractions. There are also major non-linearities generated at a spinal level in the relation between corticospinal output and the output from the motoneurone pool. For ex le, recent studies have revealed that the efficacy of the human corticospinal connection with motoneurones undergoes activity-dependent changes which influence the size of voluntary contractions. Hence, corticospinal drives must be sculpted continuously to compensate for the changing functional efficacy of the descending systems which activate the motoneurones. This highlights the need for proprioceptive monitoring of movements to ensure their accurate execution.
Publisher: Wiley
Date: 23-11-2022
DOI: 10.1113/JP282564
Abstract: Neural drive originating in higher brain areas reaches exercising limb muscles through the corticospinal‐motoneuronal pathway, which links the motor cortex and spinal motoneurones. The properties of this pathway have frequently been observed to change during fatiguing exercise in ways that could influence the development of central fatigue (i.e. the progressive reduction in voluntary muscle activation). However, based on differences in motor cortical and motoneuronal excitability between exercise modalities (e.g. single‐joint vs . locomotor exercise), there is no characteristic response that allows for a categorical conclusion about the effect of these changes on functional impairments and performance limitations. Despite the lack of uniformity in findings during fatigue, there is strong evidence for marked ‘inhibition’ of motoneurones as a direct result of voluntary drive. Endogenous forms of neuromodulation, such as via serotonin released from neurones, can directly affect motoneuronal output and central fatigue. Exogenous forms of neuromodulation, such as brain stimulation, may achieve a similar effect, although the evidence is weak. Non‐invasive transcranial direct current stimulation can cause transient or long‐lasting changes in cortical excitability however, variable results across studies cast doubt on its claimed capacity to enhance performance. Furthermore, with these studies, it is difficult to establish a cause‐and‐effect relationship between brain responsiveness and exercise performance. This review briefly summarizes changes in the corticomotoneuronal pathway during various types of exercise, and considers the relevance of these changes for the development of central fatigue, as well as the potential of non‐invasive brain stimulation to enhance motor cortical excitability, motoneuronal output and, ultimately, exercise performance. image
Publisher: Oxford University Press (OUP)
Date: 14-05-2009
Abstract: A debilitating consequence of complete spinal cord injury (SCI) is the loss of motor control. Although the goal of most SCI treatments is to re-establish neural connections, a potential complication in restoring motor function is that SCI may result in anatomical and functional changes in brain areas controlling motor output. Some animal investigations show cell death in the primary motor cortex following SCI, but similar anatomical changes in humans are not yet established. The aim of this investigation was to use voxel-based morphometry (VBM) and diffusion tensor imaging (DTI) to determine if SCI in humans results in anatomical changes within motor cortices and descending motor pathways. Using VBM, we found significantly lower gray matter volume in complete SCI subjects compared with controls in the primary motor cortex, the medial prefrontal, and adjacent anterior cingulate cortices. DTI analysis revealed structural abnormalities in the same areas with reduced gray matter volume and in the superior cerebellar cortex. In addition, tractography revealed structural abnormalities in the corticospinal and corticopontine tracts of the SCI subjects. In conclusion, human subjects with complete SCI show structural changes in cortical motor regions and descending motor tracts, and these brain anatomical changes may limit motor recovery following SCI.
Publisher: American Physiological Society
Date: 10-2011
Abstract: The objectives of the present study were to test the hypothesis that the costal diaphragm contracts during ipsilateral rotation of the trunk and that such trunk rotation increases the motor output of the muscle during inspiration. Monopolar electrodes were inserted in the right costal hemidiaphragm in six subjects, and electromyographic (EMG) recordings were made during isometric rotation efforts of the trunk to the right (“ipsilateral rotation”) and to the left (“contralateral rotation”). EMG activity was simultaneously recorded from the parasternal intercostal muscles on the right side. The parasternal intercostals were consistently active during ipsilateral rotation but silent during contralateral rotation. In contrast, the diaphragm was silent in the majority of rotations in either direction, and whenever diaphragm activity was recorded, it involved very few motor units. In addition, whereas parasternal inspiratory activity substantially increased during ipsilateral rotation and decreased during contralateral rotation, inspiratory activity in the diaphragm was essentially unaltered and the discharge frequency of single motor units in the muscle remained at 13–14 Hz in the different postures. It is concluded that 1) the diaphragm makes no significant contribution to trunk rotation and 2) even though the diaphragm and parasternal intercostals contract in a coordinated manner during resting breathing, the inspiratory output of the two muscles is affected differently by voluntary drive during trunk rotation.
Publisher: Wiley
Date: 14-06-2011
Publisher: Elsevier BV
Date: 07-2012
DOI: 10.1016/J.APMR.2012.02.009
Abstract: To investigate the mechanisms of contracture after stroke by comparing passive mechanical properties of gastrocnemius muscle-tendon units, muscle fascicles, and tendons in people with ankle contracture after stroke with control participants. Cross-sectional study. Laboratory in a research institution. A convenience s le of people with ankle contracture after stroke (n=20) and able-bodied control subjects (n=30). Not applicable. Stiffness and lengths of gastrocnemius muscle-tendon units, lengths of muscle fascicles, and tendons at specific tensions. At a tension of 100N, the gastrocnemius muscle-tendon unit was significantly shorter in participants with stroke (mean, 436mm) than in able-bodied control participants (mean, 444mm difference, 8mm 95% confidence interval [CI], 0.2-15mm P=.04). Muscle fascicles were also shorter in the stroke group (mean, 44mm) than in the control group (mean, 50mm difference, 6mm 95% CI, 1-12mm P=.03). There were no significant differences between groups in the mean stiffness or length of the muscle-tendon units and fascicles at low tension, or in the mean length of the tendons at any tension. People with ankle contracture after stroke have shorter gastrocnemius muscle-tendon units and muscle fascicles than control participants at high tension. This difference is not apparent at low tension.
Publisher: Wiley
Date: 15-12-2001
Publisher: Oxford University Press (OUP)
Date: 07-2013
DOI: 10.5665/SLEEP.2812
Publisher: Wiley
Date: 28-01-2011
Publisher: Public Library of Science (PLoS)
Date: 21-01-2016
Publisher: American Physiological Society
Date: 10-2006
DOI: 10.1152/JAPPLPHYSIOL.00103.2006
Abstract: Young women are less fatigable than young men for maximal and submaximal contractions, but the contribution of supraspinal fatigue to the sex difference is not known. This study used cortical stimulation to compare the magnitude of supraspinal fatigue during sustained isometric maximal voluntary contractions (MVCs) performed with the elbow flexor muscles of young men and women. Eight women (25.6 ± 3.6 yr, mean ± SD) and 9 men (25.4 ± 3.8 yr) performed six sustained MVCs (22-s duration each, separated by 10 s). Before the fatiguing contractions, the men were stronger than the women (75.9 ± 9.2 vs. 42.7 ± 8.0 N·m P 0.05) in control MVCs. Voluntary activation measured with cortical stimulation before fatigue was similar for the men and women during the final control MVC (95.7 ± 3.0 vs. 93.3 ± 3.6% P 0.05) and at the start of the fatiguing task ( P 0.05). By the end of the six sustained fatiguing MVCs, the men exhibited greater absolute and relative reductions in torque (65 ± 3% of initial MVC) than the women (52 ± 9% P 0.05). The increments in torque (superimposed twitch) generated by motor cortex stimulation during each 22-s maximal effort increased with fatigue ( P 0.05). Superimposed twitches were similar for men and women throughout the fatiguing task (5.5 ± 4.1 vs. 7.3 ± 4.7% P 0.05), as well as in the last sustained contraction (7.8 ± 5.9 vs. 10.5 ± 5.5%) and in brief recovery MVCs. Voluntary activation determined using an estimated control twitch was similar for the men and women at the start of the sustained maximal contractions (91.4 ± 7.4 vs. 90.4 ± 6.8%, n = 13) and end of the sixth contraction (77.2 ± 13.3% vs. 73.1 ± 19.6%, n = 10). The increase in the area of the motor-evoked potential and duration of the silent period did not differ for men and women during the fatiguing task. However, estimated resting twitch litude and the peak rates of muscle relaxation showed greater relative reductions at the end of the fatiguing task for the men than the women. These results indicate that the sex difference in fatigue of the elbow flexor muscles is not explained by a difference in supraspinal fatigue in men and women but is largely due to a sex difference of mechanisms located within the elbow flexor muscles.
Publisher: American Physiological Society
Date: 05-2020
DOI: 10.1152/JAPPLPHYSIOL.00741.2019
Abstract: It is generally accepted that proprioceptive ability deteriorates with age, although not all data support this view. We tested proprioception using three reliable tests at the ankle in 80 adults (19–80 yr). For all tests, the effects of muscle thixotropy were controlled. Under these conditions, we found no difference in proprioceptive acuity between young and old people.
Publisher: Springer Science and Business Media LLC
Date: 10-05-2016
Publisher: Elsevier BV
Date: 05-2017
DOI: 10.1016/J.RESP.2017.02.004
Abstract: Quantitatively measure and validate analysis of neural respiratory drive (NRD) using a commercial polysomnography system in children during sleep. Surface electromyogram of the diaphragm (sEMGdi) recorded from primary snoring children were analysed. A subset was re-analysed to assess intra- and inter-investigator reproducibility. Effects of different band pass filter settings (20-100Hz vs 10-1000Hz) on sEMGdi litude were evaluated. Mean sEMGdi from 45 children aged 4.38 years (median IQR 3.00-7.96) was 5.05μV (SD 2.73). The sEMGdi had a high intra-subject intraclass correlation coefficient (ICC) of 0.88. sEMGdi analysis was reproducible with high ICC between occasions (0.99 95% CI 0.98-0.99) and between investigators (0.98 95% CI 0.97-0.99). There was also a high ICC (0.99, 95% CI 0.96-1.00) between the sEMGdi measured using different band-pass filter settings. Age and BMI were negative predictors of sEMGdi (p<0.0001 and p=0.0004 respectively). NRD in children during sleep as assessed by sEMGdi can be quantified in a reliable and reproducible fashion.
Publisher: American Physiological Society
Date: 08-2007
DOI: 10.1152/JAPPLPHYSIOL.00220.2007
Abstract: During sustained maximal voluntary contractions (MVCs), most fatigue occurs within the muscle, but some occurs because voluntary activation of the muscle declines (central fatigue), and some of this reflects suboptimal output from the motor cortex (supraspinal fatigue). This study examines whether supraspinal fatigue occurs during a sustained submaximal contraction of 5% MVC. Eight subjects sustained an isometric elbow flexion of 5% MVC for 70 min. Brief MVCs were performed every 3 min, with stimulation of the motor point, motor cortex, and brachial plexus. Perceived effort and pain, elbow flexion torque, and surface EMGs from biceps and brachioradialis were recorded. During the sustained 5% contraction, perceived effort increased from 0.5 to 3.9 (out of 10), and elbow flexor EMG increased steadily by ∼60–80%. Torque during brief MVCs fell to 72% of control values, while both the resting twitch and EMG declined progressively. Thus the sustained weak contraction caused fatigue, some of which was due to peripheral mechanisms. Voluntary activation measured by motor point and motor cortex stimulation methods fell to 90% and 80%, respectively. Thus some of the fatigue was central. Calculations based on the fall in voluntary activation measured with cortical stimulation indicate that about two-thirds of the fatigue was due to supraspinal mechanisms. Therefore, sustained performance of a very low-force contraction produces a progressive inability to drive the motor cortex optimally during brief MVCs. The effect of central fatigue on performance of the weak contraction is less clear, but it may contribute to the increase in perceived effort.
Publisher: Wiley
Date: 21-02-2005
Publisher: Oxford University Press (OUP)
Date: 04-2015
DOI: 10.5665/SLEEP.4566
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 15-07-2008
DOI: 10.1016/J.PAIN.2007.08.032
Abstract: Spinal cord injury (SCI) results in deafferentation and the onset of neuropathic pain in a substantial proportion of people. Based on evidence suggesting motor cortex activation results in attenuation of neuropathic pain, we sought to determine whether neuropathic SCI pain could be modified by imagined movements of the foot. Fifteen subjects with a complete thoracic SCI (7 with below-level neuropathic pain and 8 without pain) were instructed in the use of movement imagery. Movement imagery was practiced three times daily for 7days. On the eighth day, subjects performed the movement imagery in the laboratory and recorded pain ratings during the period of imagined movement. Six out of 7 subjects with neuropathic pain reported an increase in pain during imagined movements from 2.9+/-0.7 during baseline to 5.0+/-1.0 during movement imagery (p<0.01). In SCI subjects without neuropathic pain, movement imagery evoked an increase in non-painful sensation intensity from a baseline of 1.9+/-0.7 to 4.8+/-1.3 during the movement imagery (p<0.01). Two subjects without a history of pain or non-painful phantom sensations had onset of dysesthesia while performing imagined movements. This study reports exacerbation of pain in response to imagined movements and it contrasts with reports of pain reduction in people with peripheral neuropathic pain. The potential mechanisms underlying this sensory enhancement with movement imagery are discussed.
Publisher: Wiley
Date: 03-2006
Publisher: Public Library of Science (PLoS)
Date: 02-12-2015
Publisher: Elsevier BV
Date: 03-2012
DOI: 10.1016/J.RESP.2011.11.017
Abstract: Increases in lung volume inhibit the inspiratory output from the medulla, but the effect of lung inflation on the voluntary control of breathing in humans is not known. We tested corticospinal excitability using transcranial magnetic stimulation (TMS) to evoke a response in the scalene muscles. TMS was delivered at rest at three different lung volumes between functional residual capacity (FRC) and total lung capacity (TLC) during incremental inspiratory and incremental expiratory manoeuvres. Motor evoked potentials (MEPs) in scalenes were ∼50% larger at a high lung volume (FRC+∼90% inspiratory capacity [IC]) compared to lower lung volumes (FRC and FRC+∼40% IC) in both inspiratory and expiratory manoeuvres (p<0.001). The change in MEP size was not due to differences in pre-stimulus EMG litude (p=0.29). The results suggest a differential effect of lung inflation on the automatic and voluntary control of breathing in humans.
Publisher: Springer Science and Business Media LLC
Date: 19-05-2009
DOI: 10.1007/S00221-009-1832-3
Abstract: Along with afferent information, centrally generated motor command signals may play a role in joint position sense. Isometric muscle contractions can produce a perception of joint displacement in the same direction as the joint would move if unrestrained. Contradictory findings of perceived joint displacement in the opposite direction have been reported. As this only occurs if muscle spindle discharge in the contracting muscle is initially low, it may reflect increased muscle spindle firing from fusimotor activation, rather than central motor command signals. Methodological differences including the muscle contraction task and use of muscle conditioning could underlie the opposing findings. Hence, we tested perceived joint position during two contraction tasks ('hold force' and 'hold position') at the same joint (wrist) and controlled muscle spindle discharge with thixotropic muscle conditioning. We expected that prior conditioning of the contracting muscle would eliminate any effect of increased fusimotor activation, but not of central motor commands. Muscle conditioning altered perceived wrist position as expected. Further, during muscle contractions, subjects reported wrist positions displaced ~12 degrees in the direction of contraction, despite no change in wrist position. This was similar for 'hold force' and 'hold position' tasks and occurred despite prior conditioning of the agonist muscle. However, conditioning of the antagonist muscle did reduce the effect of voluntary contraction on position sense. The errors in position sense cannot be explained by fusimotor activation. We propose that central signals combine with afferent signals to determine limb position and that multiple sources of information are weighted according to their reliability.
Publisher: American Physiological Society
Date: 07-2004
DOI: 10.1152/JAPPLPHYSIOL.01336.2003
Abstract: Voluntary activation of muscle is commonly quantified by comparison of the extra force added by motor nerve stimulation during a contraction [superimposed twitch (SIT)] with that produced at rest by the same stimulus (resting twitch). An inability to achieve 100% voluntary activation implies that failure to produce maximal force output from the muscle must have occurred at a site at or above the level of the motoneurons. We have used cortical stimulation to quantify voluntary activation. Here, incomplete activation implies a failure at or above the level of motor cortical output. With cortical stimulation, it is inappropriate to compare extra force evoked during a contraction with the twitch evoked in resting muscle because motor cortical and spinal cord excitability both increase with activity. However, an appropriate “resting twitch” can be estimated. We previously estimated its litude by extrapolation of the linear relation between SIT litude and voluntary torque calculated from 35 contractions of % maximum (Todd G, Taylor JL, and Gandevia SC. J Physiol 551: 661–671, 2003). In this study, we improved the utility of this method to enable evaluation of voluntary activation when it may be changing over time, such as during the development of fatigue, or in patients who may be unable to perform large numbers of contractions. We have reduced the number of contractions required to only three. Estimation of the resting twitch from three contractions was reliable over time with low variability. Furthermore, its reliability and variability were similar to the resting twitch estimated from 30 contractions and to that evoked by conventional motor nerve stimulation.
Publisher: American Physiological Society
Date: 09-2022
Publisher: Oxford University Press (OUP)
Date: 1994
Abstract: Many people previously affected by polio complain of increased fatigue, weakness and pain many years after the initial illness. Although electromyographic abnormalities have been found in these patients, the cause of their increased weakness is not well understood. Previous studies have shown decreased strength and impaired exercise performance in those with prior polio, but the level of voluntary drive to the muscle has not been investigated. The present study investigated maximal voluntary activation without fatigue and both peripheral and central components of muscle fatigue during exercise in 21 subjects with poliomyelitis 20-40 years previously, and 20 healthy, age-matched control subjects. Voluntary activation and strength of the elbow flexors were quantified using twitch interpolation during maximal isometric voluntary contractions both at rest, and during fatigue induced by 45 min of repeated isometric contractions. Compared with the control subjects, patients with prior polio had impaired voluntary activation both when the elbow flexors were not fatigued and during fatiguing submaximal exercise. During exercise, polio subjects also had lower twitch litudes and increased subjective fatigue. Central and peripheral fatigue were more marked in those with the post-polio syndrome. The impaired voluntary activation with unfatigued muscles in polio subjects indicates that defective central or reflex drive may contribute to their new weakness.
Publisher: Oxford University Press (OUP)
Date: 1989
Abstract: In the cat and monkey the fastest axons in the peripheral nerve are group I afferents from muscle, but there are no definitive data on conduction velocity for these afferents in human subjects. Knowledge of the relative conduction velocities of muscle and cutaneous afferents is important for the interpretation of reflex studies, evoked potentials and other aspects of motor control. To rectify this deficiency, the conduction velocities of the fastest muscle and cutaneous afferents were determined for the median, ulnar and tibial nerves of normal subjects. Low-threshold muscle afferents innervating abductor pollicis brevis, abductor digiti minimi and abductor hallucis were stimulated selectively through a microelectrode inserted percutaneously at the motor point. Low-threshold cutaneous afferents were stimulated with ring electrodes around the proximal phalanx of digits II or V for the upper limb and digit II for the lower limb. Compound action potentials were recorded with bipolar near-nerve electrodes at two sites in the proximal limb segment and conduction velocities of the fastest afferents in the neural volley calculated. The mean conduction velocities of the muscle and cutaneous afferents were, respectively, 74.7 +/- 6.5 m.s-1 and 80.3 +/- 6.7 m.s-1 for the median nerve, 67.5 +/- 10.2 m.s-1 and 67.5 +/- 10.5 m.s-1 for the ulnar nerve, and 54.7 +/- 3.4 m.s-1 and 52.8 +/- 3.2 m.s-1 for the tibial nerve. For upper and lower limb nerves the conduction velocities of low-threshold muscle and cutaneous afferents were not significantly different when measured over the same proximal segment.
Publisher: Elsevier BV
Date: 2011
DOI: 10.1016/J.RESP.2010.08.023
Abstract: In voluntary breaths, driven through the motor cortex, the pattern of activation in human inspiratory intercostal muscles is unknown. We measured single motor unit behaviour in the first, third, and fifth parasternal intercostal muscles in 5 subjects for 'quiet' and matched 'voluntary' inspirations. In voluntary breaths, the average onset, peak and end discharge rate of 264 inspiratory single motor units was greater in the first interspace compared to caudal spaces (p < 0.05). Relative to the onset of inspiratory flow, the time of recruitment of single motor units and the onset of multiunit activity were also earlier in the first compared to the fifth interspace (p < 0.05). For 215 'common' motor units, peak discharge frequencies were ∼20% higher in voluntary compared to quiet breaths (p < 0.05), due in part, to small differences in the pattern of breathing. A rostrocaudal gradient of motor unit activation across parasternal intercostal muscles was preserved in voluntary and involuntary tasks. A common mechanism may mediate this pattern of recruitment.
Publisher: American Physiological Society
Date: 10-2003
DOI: 10.1152/JAPPLPHYSIOL.00939.2002
Abstract: Posteroanterior stiffness of the lumbar spine is influenced by factors, including trunk muscle activity and intra-abdominal pressure (IAP). Because these factors vary with breathing, this study investigated whether stiffness is modulated in a cyclical manner with respiration. A further aim was to investigate the relationship between stiffness and IAP or abdominal and paraspinal muscle activity. Stiffness was measured from force-displacement responses of a posteroanterior force applied over the spinous process of L 2 and L 4 . Recordings were made of IAP and electromyographic activity from L 4 /L 2 erector spinae, abdominal muscles, and chest wall. Stiffness was measured with the lung volume held at the extremes of tidal volume and at greater and lesser volumes. Stiffness at L 4 and L 2 increased above base-level values at functional residual capacity (L 2 14.9 N/mm and L 4 15.3 N/mm) with both inspiratory and expiratory efforts. The increase was related to the respiratory effort and was greatest during maximum expiration (L 2 24.9 N/mm and L 4 23.9 N/mm). The results indicate that changes in trunk muscle activity and IAP with respiratory efforts modulate spinal stiffness. In addition, the diaphragm may augment spinal stiffness via attachment of its crural fibers to the lumbar vertebrae.
Publisher: Wiley
Date: 09-05-2006
Publisher: Wiley
Date: 24-03-2004
DOI: 10.1002/MUS.20027
Abstract: Accurate measurement of muscle strength and voluntary muscle activation is important in the assessment of disorders that affect the motor pathways or muscle. We designed a multipurpose system to assess the variability and reproducibility of isometric torque measurements obtained during maximal voluntary efforts of the knee flexor, knee extensor, ankle dorsiflexor, and ankle plantarflexor muscles on each side. It used two isometric myographs mounted on an adjustable frame. Measurements of maximal voluntary torque (range, 25-188 Nm) displayed low variability within a testing session and over five testing sessions (coefficient of variation range, 5-11%). We used the same equipment to measure voluntary activation of the triceps surae muscles. Voluntary activation, measured with a sensitive twitch interpolation method, increased with increasing voluntary contraction torque (P < 0.001) and was very high during maximal efforts (mean, 97.8 +/- 2.1% median, 98.5%). Furthermore, measurements of voluntary activation during maximal efforts were reproducible across testing sessions with very little variability (coefficient of variation, <2%). The myograph system and the testing procedures should allow accurate measurement of strength and voluntary drive in longitudinal patient studies.
Publisher: Elsevier BV
Date: 04-2012
DOI: 10.1016/J.RESP.2012.02.006
Abstract: The short-latency reflex inhibition of human inspiratory muscles produced by loading is prolonged in asthma and obstructive sleep apnoea, both diseases involving airway and systemic inflammation. Both diseases also involve repetitive inspiratory loading. Although airway mucosal afferents are not critical components of the normal reflex arc, during airway inflammation, prolongation of the reflex may be caused by altered mucosal afferent sensitivity, or altered central processing of their inputs. We hypothesised that acute viral airway inflammation would replicate the reflex abnormality. The reflex was tested in 9 subjects with a "common cold" during both the acute infection and when well. Surface electrodes recorded electromyographic (EMG) activity bilaterally from scalene muscles. Latencies of the inhibitory response (IR) did not differ significantly (IR peak 67 vs 70 ms (p=0.12), and IR offset 87 vs 90 ms (p=0.23), between the inflamed and well conditions, respectively). There was no difference in any measure of the size of the reflex inhibition.
Publisher: Wiley
Date: 28-07-2011
Publisher: Oxford University Press (OUP)
Date: 12-04-2005
Publisher: Springer Science and Business Media LLC
Date: 24-02-2015
DOI: 10.1007/S11910-015-0537-1
Abstract: Obstructive sleep apnoea (OSA) is linked to local neural injury that evokes airway muscle remodelling. The upper airway muscles of patients with OSA are exposed to intermittent hypoxia as well as vibration induced by snoring. A range of electrophysiological and other studies have established altered motor and sensory function of the airway in OSA. The extent to which these changes impair upper airway muscle function and their relationship to the progression of OSA remains undefined. This review will collate the evidence for upper airway remodelling in OSA, particularly the electromyographic changes in upper airway muscles of patients with OSA.
Publisher: Society for Neuroscience
Date: 14-09-2005
DOI: 10.1523/JNEUROSCI.0923-05.2005
Abstract: The sartorius muscle is the longest muscle in the human body. It is strap-like, up to 600 mm in length, and contains five to seven neurovascular compartments, each with a neuromuscular endplate zone. Some of its fibers terminate intrafascicularly, whereas others may run the full length of the muscle. To assess the location and timing of activation within motor units of this long muscle, we recorded electromyographic potentials from multiple intramuscular electrodes along sartorius muscle during steady voluntary contraction and analyzed their activity with spike-triggered averaging from a needle electrode inserted near the proximal end of the muscle. Approximately 30% of sartorius motor units included muscle fibers that ran the full length of the muscle, conducting action potentials at 3.9 ± 0.1 m/s. Most motor units were innervated within a single muscle endplate zone that was not necessarily near the midpoint of the fiber. As a consequence, action potentials reached the distal end of a unit as late as 100 ms after initiation at an endplate zone. Thus, contractile activity is not synchronized along the length of single sartorius fibers. We postulate that lateral transmission of force from fiber to endomysium and a wide distribution of motor unit endplates along the muscle are critical for the efficient transmission of force from sarcomere to tendon and for the prevention of muscle injury caused by overextension of inactive regions of muscle fibers.
Publisher: Wiley
Date: 29-10-2010
DOI: 10.1111/J.1460-9568.2010.07444.X
Abstract: Muscle fatigue is defined as an exercise-induced reduction in the force-generating capacity of muscle. Here, we investigated the effect of muscle fatigue on hand dexterity. Healthy adults (n = 17) gripped and lifted an object (0.342 kg) five times before and after two interventions. The interventions, performed on separate days, involved 2 min of rest (control) or sustained maximal pinch grip that reduced maximal force by 60% (fatigue). Horizontal grip force (GF), vertical lift force (LF) and first dorsal interosseous electromyographic activity (EMG) were measured. The lift (dynamic) and hold (stationary) phase of the task were analysed. Before the intervention, there was no significant difference between the control and fatigue conditions for the 15 measured parameters. However, post-intervention GF was reduced with fatigue compared with the control condition (hold phase), whereas GF coefficient of variation (hold phase) and root mean square EMG (lift phase) increased with fatigue. Fatigue also disrupted the temporal relationship between GF and LF (assessed by cross-correlation of the derivative of GF and LF). The maximum cross-correlation coefficient was significantly reduced with fatigue compared with the control condition. Grip strategy and the kinetics of the lifting movement (minimum LF, maximum LF, maximum derivative of LF, and maximum acceleration) were unchanged with fatigue. Our results suggest that fatigued subjects generate more EMG to lift and hold an object but produce less force and are less able to match changes in LF with changes in GF. Fatigued subjects also exhibit greater fluctuation in GF while holding objects.
Publisher: Wiley
Date: 12-01-2023
DOI: 10.1113/JP284271
Publisher: Elsevier BV
Date: 10-2018
DOI: 10.1016/J.MEHY.2018.07.015
Abstract: Fundamental to the advancement of scientific knowledge is unbiased, accurate and validated measurement techniques. Recent United Nations and landmark Nature publications highlight the global uptake of mobile technology and the staggering potential for big data to encourage people to be physically active and to influence health policy. However, concerns exist about inconsistencies in smartphone health apps. Big data has many benefits, but noisy data may lead to wrong conclusions. In reaction to the increasing availability of low quality data we call for a rigorous debate into the validity of substituting big data for accurate data in health research. We evaluated the step counting accuracy of a smartphone app previously used by 717,527 people from 111 countries. Our new data (from 48 participants aged 21-59 years body mass index 17.7-33.5 kg/m
Publisher: Public Library of Science (PLoS)
Date: 17-11-2021
DOI: 10.1371/JOURNAL.PONE.0259988
Abstract: Passively grasping an unseen artificial finger induces ownership over this finger and an illusory coming together of one’s index fingers: a grasp illusion. Here we determine how interoceptive ability and attending to the upper limbs influence this illusion. Participants passively grasped an unseen artificial finger with their left index finger and thumb for 3 min while their right index finger, located 12 cm below, was lightly cl ed. Experiment 1 (n = 30) investigated whether the strength of the grasp illusion (perceived index finger spacing and perceived ownership) is related to a person’s level of interoceptive accuracy (modified heartbeat counting task) and sensibility ( Noticing subscale of the Multidimensional Assessment of Interoceptive Awareness). Experiment 2 (n = 30) investigated the effect of providing verbal or tactile cues to guide participants’ attention to their upper limbs. On their own, neither interoceptive accuracy and sensibility or verbal and tactile cueing had an effect on the grasp illusion. However, verbal cueing increased the strength of the grasp illusion in in iduals with lower interoceptive ability. Across the observed range of interoceptive accuracy and sensibility, verbal cueing decreased perceived index spacing by 5.6 cm [1.91 to 9.38] (mean [95%CI]), and perceived ownership by ∼3 points on a 7-point Likert scale (slope -0.93 [-1.72 to -0.15]). Thus, attending to the upper limbs via verbal cues increases the strength of the grasp illusion in a way that is inversely proportional to a person’s level of interoceptive accuracy and sensibility.
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 06-2007
End Date: 10-2011
Amount: $420,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2004
End Date: 12-2008
Amount: $605,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2005
End Date: 12-2006
Amount: $323,400.00
Funder: Australian Research Council
View Funded ActivityStart Date: 08-2022
End Date: 07-2027
Amount: $5,000,000.00
Funder: Australian Research Council
View Funded Activity