ORCID Profile
0000-0002-2465-6026
Current Organisations
German Cancer Research Center
,
University of South Australia
,
Laboratório Nacional de Computação Científica
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Publisher: Public Library of Science (PLoS)
Date: 18-12-2012
Publisher: American Physiological Society
Date: 09-2023
Abstract: Seven core concepts, including cell-cell communication, were identified by an Australian Delphi task force of physiology educators. The previously “unpacked” concept was adapted for Australian educators and students to develop a framework with seven themes and 60 subthemes. The framework was successfully validated by the original Delphi panel of educators and will provide a valuable resource for teaching and learning in Australian universities.
Publisher: Elsevier BV
Date: 09-2020
Publisher: American Physiological Society
Date: 08-2006
DOI: 10.1152/JAPPLPHYSIOL.01399.2005
Abstract: Repetitive transcranial magnetic stimulation of the motor cortex (rTMS) can be used to modify motor cortical excitability in human subjects. At stimulus intensities near to or above resting motor threshold, low-frequency rTMS (∼1 Hz) decreases motor cortical excitability, whereas high-frequency rTMS (5–20 Hz) can increase excitability. We investigated the effect of 10 min of intermittent rTMS on motor cortical excitability in normal subjects at two frequencies (2 or 6 Hz). Three low intensities of stimulation (70, 80, and 90% of active motor threshold) and sham stimulation were used. The number of stimuli were matched between conditions. Motor cortical excitability was investigated by measurement of the motor-evoked potential (MEP) evoked by single magnetic stimuli in the relaxed first dorsal interosseus muscle. The intensity of the single stimuli was set to evoke baseline MEPs of ∼1 mV in litude. Both 2- and 6-Hz stimulation, at 80% of active motor threshold, reduced the magnitude of MEPs for ∼30 min ( P 0.05). MEPs returned to baseline values after a weak voluntary contraction. Stimulation at 70 and 90% of active motor threshold and sham stimulation did not induce a significant group effect on MEP magnitude. However, the intersubject response to rTMS at 90% of active motor threshold was highly variable, with some subjects showing significant MEP facilitation and others inhibition. These results suggest that, at low stimulus intensities, the intensity of stimulation may be as important as frequency in determining the effect of rTMS on motor cortical excitability.
Publisher: Public Library of Science (PLoS)
Date: 03-2021
DOI: 10.1371/JOURNAL.PONE.0247920
Abstract: Transcranial sonography is increasingly used to aid clinical diagnoses of movement disorders, for ex le, to identify an enlarged area of substantia nigra echogenicity in patients with Parkinson’s disease. The current study investigated characteristics of the midbrain at the anatomical plane for quantification of substantia nigra echogenicity. METHODS: Area of substantia nigra echogenicity, cross-sectional area of the midbrain, and interpeduncular angle were quantified in two groups of adults aged 18–50 years: 47 healthy non-drug-using controls (control group) and 22 in iduals with a history of meth hetamine use (meth hetamine group), a cohort with a high prevalence of enlarged substantia nigra echogenicity and thus risk of Parkinson’s disease. In the control group, cross-sectional area of the midbrain (4.47±0.44 cm 2 ) and interpeduncular angle were unaffected by age, sex, or image acquisition side. In the meth hetamine group, cross-sectional midbrain area (4.72±0.60 cm 2 ) and area of substantia nigra echogenicity were enlarged compared to the control group, and the enlargement was sex-dependent (larger in males than females). Whole midbrain area and interpeduncular angle were found to be weak predictors of area of substantia nigra echogenicity after accounting for group and sex. History of meth hetamine use is associated with an enlarged midbrain and area of substantia nigra echogenicity, and the abnormality is more pronounced in males than females. Thus, males may be more susceptible to meth hetamine-induced changes to the brainstem, and risk of Parkinson’s disease, than females.
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: Elsevier BV
Date: 05-2019
DOI: 10.1016/J.CLINPH.2019.02.005
Abstract: The study aim was to determine if use of illicit hetamines or ecstasy is associated with abnormal excitability of the corticomotoneuronal pathway and manipulation of novel objects with the hand. Three groups of adults aged 18-50 years were investigated: in iduals with a history of illicit hetamine use, in iduals with a history of ecstasy use but minimal use of other stimulants, and non-drug users. Transcranial magnetic stimulation was delivered to the motor cortex and the electromyographic response (motor evoked potential MEP) was recorded from a contralateral hand muscle. Participants also gripped and lifted a novel experimental object consisting of two strain gauges and an accelerometer. Resting MEP litude was larger in the hetamine group (6M, 6F) than the non-drug and ecstasy groups (p < 0.005) in males but not females. Overestimation of grip force during manipulation of a novel object was observed in the hetamine group (p = 0.020) but not the ecstasy group. History of illicit hetamine use, in particular meth hetamine, is associated with abnormal motor cortical and/or corticomotoneuronal excitability in males and abnormal manipulation of novel objects in both males and females. Abnormal excitability and hand function is evident months to years after cessation of illicit hetamine use.
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: Wiley
Date: 16-03-2006
DOI: 10.1111/J.1440-1681.2006.04363.X
Abstract: 1. Muscle fatigue can be defined as any exercise-induced loss of ability to produce force with a muscle or muscle group. It involves processes at all levels of the motor pathway between the brain and the muscle. Central fatigue represents the failure of the nervous system to drive the muscle maximally. It is defined as a progressive exercise-induced reduction in voluntary activation or neural drive to the muscle. Supraspinal fatigue is a component of central fatigue. It can be defined as an exercise-induced decline in force caused by suboptimal output from the motor cortex. 2. When stimulus intensity is set appropriately, transcranial magnetic stimulation (TMS) over the motor cortex during an isometric maximal voluntary contraction (MVC) of the elbow flexors commonly evokes a small twitch-like increment in flexion force. This increment indicates that, despite the subject's maximal effort, motor cortical output at the moment of stimulation was not maximal and was not sufficient to drive the motoneurons to produce maximal force from the muscle. An exercise-induced increase in this increment demonstrates supraspinal fatigue. 3. Supraspinal fatigue has been demonstrated during fatiguing sustained and intermittent maximal and submaximal contractions of the elbow flexors where it accounts for about one-quarter of the loss of force of fatigue. It is linked to activity and the development of fatigue in the tested muscles and is little influenced by exercise performed by other muscles. 4. The mechanisms of supraspinal fatigue are unclear. Although changes in the behaviour of cortical neurons and spinal motoneurons occur during fatigue, they can be dissociated from supraspinal fatigue. One factor that may contribute to supraspinal fatigue is the firing of fatigue-sensitive muscle afferents that may act to impair voluntary descending drive.
Publisher: The University of Kansas
Date: 06-03-2022
Abstract: The field of distributional ecology has seen considerable recent attention, particularly surrounding the theory, protocols, and tools for Ecological Niche Modeling (ENM) or Species Distribution Modeling (SDM). Such analyses have grown steadily over the past two decades—including a maturation of relevant theory and key concepts—but methodological consensus has yet to be reached. In response, and following an online course taught in Spanish in 2018, we designed a comprehensive English-language course covering much of the underlying theory and methods currently applied in this broad field. Here, we summarize that course, ENM2020, and provide links by which resources produced for it can be accessed into the future. ENM2020 lasted 43 weeks, with presentations from 52 instructors, who engaged with participants globally through ,000 hours of viewing and ,000 views of instructional video and question-and-answer sessions. Each major topic was introduced by an “Overview” talk, followed by more detailed lectures on subtopics. The hierarchical and modular format of the course permits updates, corrections, or alternative viewpoints, and generally facilitates revision and reuse, including the use of only the Overview lectures for introductory courses. All course materials are free and openly accessible (CC-BY license) to ensure these resources remain available to all interested in distributional ecology.
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: Springer Science and Business Media LLC
Date: 22-12-2006
DOI: 10.1007/S00421-006-0371-X
Abstract: During exercises with relatively small muscle masses, limitations to exercise performance by the cardiovascular system should be significantly reduced, allowing one to fully-test the "oxidative potential" of the investigated muscles. Ten elderly males (E, 77.8 +/- 2.9 years [x +/- SD]) and eight young controls (Y, 26.6 +/- 3.0) underwent incremental exercises to voluntary exhaustion on a dynamic leg-extension (dominant limb) machine (knee-extension, KE) and on a cycloergometer (CYCLO). During KE the load was increased every 3 min to loads corresponding to 20, 40 and 60% of the force of one-repetition maximum (1RM). The following variables were determined (vastus lateralis muscle): concentration changes of deoxygenated haemoglobin and myoglobin (Delta[deoxy(Hb + Mb)]) by near-infrared spectroscopy (NIRS), expressed as percentage of the maximal value obtained during transient limb ischemia, and taken as an index of O2 extraction root mean square (RMS) and median power frequency (MDF) by electromyography. The total lifted load during KE and peak workload during CYCLO were lower in E versus Y (620.4 +/- 321.9 kg vs. 1347.4 +/- 458.7 113.5 +/- 23.9 W vs. 224.3 +/- 41.0, respectively). During CYCLO Delta[deoxy(Hb + Mb)] peak (i.e. the value determined at exhaustion) was lower in E (44.5 +/- 17.7%) versus Y (67.1 +/- 22.9), whereas during KE Delta[deoxy(Hb + Mb)] peak was higher in E (56.8 +/- 20.9%) versus Y (38.6 +/- 15.8). "Thresholds", that is abrupt increases in RMS slopes, were detected in Y but not in E, suggesting less recruitment or a preferential atrophy of type 2 fibers in the elderly. These findings, associated with the preserved capacity of O2 extraction, suggest a shift towards oxidative metabolism in skeletal muscles of 78 year-old subjects, which could preserve, at least in part, their capacity to carry out exercise.
Publisher: American Physiological Society
Date: 07-2010
DOI: 10.1152/JAPPLPHYSIOL.00782.2009
Abstract: “Central” and “peripheral” limitations to oxidative metabolism during exercise were evaluated in 10 young males following a 35-day horizontal bed rest (BR). Incremental exercise (IE) and moderate- and heavy-intensity constant-load exercises (CLE) were carried out on a cycloergometer before and 1–2 days after BR. Pulmonary gas exchange, cardiac output (Q̇ by impedance cardiography), skeletal muscle (vastus lateralis), and brain (frontal cortex) oxygenation (by near-infrared spectroscopy) were determined. After BR, “peak” (values at exhaustion during IE) workload, peak O 2 uptake (V̇o 2peak ), peak stroke volume, Q̇ peak , and peak skeletal muscle O 2 extraction were decreased (−18, −18, −22, −19, and −33%, respectively). The gas exchange threshold was ∼60% of V̇o 2peak both before and after BR. At the highest workloads, brain oxygenation data suggest an increased O 2 extraction, which was unaffected by BR. V̇o 2 kinetics during CLE (same percentage of peak workload before and after BR) were slower (time constant of the “fundamental” component: 31.1 ± 2.0 s before vs. 40.0 ± 2.2 s after BR) the litude of the “slow component” was unaffected by BR, thus it would be greater, after BR, at the same absolute workload. A more pronounced “overshoot” of skeletal muscle O 2 extraction during CLE was observed after BR, suggesting an impaired adjustment of skeletal muscle O 2 delivery. The role of skeletal muscles in the impairment of oxidative metabolism during submaximal and maximal exercise after BR was identified. The reduced capacity of peak cardiovascular O 2 delivery did not determine a “competition” for the available O 2 between skeletal muscles and brain.
Publisher: American Physiological Society
Date: 05-2009
DOI: 10.1152/JAPPLPHYSIOL.91364.2008
Abstract: Repetitive transcranial magnetic stimulation (rTMS) can induce short-term reorganization of human motor cortex. Here, we investigated the effect of rTMS during relaxation and weak voluntary muscle contraction on motor cortex excitability and hand function. Subjects ( n = 60) participated in one of four studies. Single transcranial magnetic stimuli were delivered over the motor area of the first dorsal interosseus for measurement of motor evoked potential (MEP) size before and after real or sham rTMS delivered at an intensity of 80% of active motor threshold. rTMS involved trains of stimuli applied at 6 Hz for 5 s and repeated every 30 s for 10 min. Resting MEP size was suppressed for 15 min after rTMS during relaxation. However, MEP suppression was abolished when additional brief voluntary contractions were performed before and after rTMS ( study 1). Resting MEP size was suppressed for 30 min after rTMS during weak voluntary contraction. MEP suppression was present even though voluntary contractions were performed before and after rTMS ( study 2). The MEP suppression most likely reflects a decrease in motor cortical excitability. Surprisingly, rTMS during voluntary contraction did not alter maximal finger tapping speed or performance on a grooved pegboard test, object grip and lift task ( study 3), and visuomotor tracking task ( study 4). These studies document the complex relationship between voluntary movement and rTMS-induced plasticity in motor cortex. This work has implications for the optimization of rTMS parameters for improved efficacy and potential therapeutic applications.
Publisher: Public Library of Science (PLoS)
Date: 13-02-2013
Publisher: Elsevier BV
Date: 10-2021
Publisher: American Physiological Society
Date: 09-2023
Abstract: This article unpacks the core concept of the “movement of substances” within the body, with the aim to produce a resource that will help guide the teaching of physiology at tertiary education institutes in Australia. The concept introduces fundamental knowledge of the factors that drive substance movement and then applies them in physiological contexts.
Publisher: Wiley
Date: 23-09-2013
DOI: 10.1002/HUP.2351
Abstract: To investigate movement speed and rhythmicity in abstinent cannabis users, we hypothesized that abstinent cannabis users exhibit decreased maximal finger tapping frequency and increased variability of tapping compared with non-drug users. The study involved 10 healthy adult cannabis users and 10 age-matched and gender-matched controls with no history of illicit drug use. Subjects underwent a series of screening tests prior to participation. Subjects were then asked to tap a strain gauge as fast as possible with the index finger of their dominant hand (duration 5 s). The average intertap interval did not significantly differ between groups, but the coefficient of variation of the intertap interval was significantly greater in the cannabis group than in controls (p=0.011). The cannabis group also exhibited a slow tapping frequency at the beginning of the task. Rhythmicity of finger tapping is abnormal in in iduals with a history of cannabis use. The abnormality appears to be long lasting and adds to the list of functional changes present in abstinent cannabis users.
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: American Physiological Society
Date: 09-2023
Abstract: The “cell membrane” core concept was unpacked by a team of Australian physiology educators into a conceptual framework to provide guidance for students and educators. Key themes in the cell membrane core concept were cell membrane definition and structure, transport across cell membranes, and membrane potentials. Australian educators reviewing the framework identified cell membrane as an essential yet relatively simple core concept, suggesting that this is well-placed in foundational physiology courses across a erse range of degrees.
Publisher: Elsevier BV
Date: 04-2016
DOI: 10.1016/J.PARKRELDIS.2016.02.019
Abstract: The sonographic appearance of the substantia nigra is abnormally bright and enlarged (hyperechogenic) in young adults with a history of illicit stimulant use. The abnormality is a risk factor for Parkinson's disease. The aim of the current study was to identify the type of illicit stimulant drug associated with substantia nigra hyperechogenicity and to determine if in iduals with a history of illicit stimulant use exhibit clinical signs of parkinsonism. We hypothesised that use of hetamines (primarily meth hetamine) is associated with substantia nigra hyperechogenicity and clinical signs of parkinsonism. The area of echogenic signal in the substantia nigra was measured in abstinent human hetamine users (n = 27 33 ± 8 years) and in three control groups comprising a) 'ecstasy' users (n = 19 23 ± 3 years), b) cannabis users (n = 30 26 ± 8 years), and c) non-drug users (n = 37 25 ± 7 years). A subset of subjects (n = 55) also underwent a neurological examination comprising the third and fifth part of the Unified Parkinson's Disease Rating Scale. Area of substantia nigra echogenicity was significantly larger in the hetamine group (0.276 ± 0.080 cm(2)) than in the control groups (0.200 ± 0.075, 0.190 ± 0.049, 0.191 ± 0.055 cm(2), respectively P < 0.002). The score on the clinical rating scale was also significantly higher in the hetamine group (8.4 ± 8.1) than in pooled controls (3.3 ± 2.8 P = 0.002). Illicit use of hetamines is associated with abnormal substantia nigra morphology and subtle clinical signs of parkinsonism. The results support epidemiological findings linking use of hetamines, particularly meth hetamine, with increased risk of developing Parkinson's disease later in life.
Publisher: Springer Science and Business Media LLC
Date: 17-12-2012
Publisher: American Physiological Society
Date: 02-2008
Publisher: Hindawi Limited
Date: 2017
DOI: 10.1155/2017/3673159
Abstract: We present clinical features and substantia nigra morphology for two brothers with Parkinson’s disease (PD) aged 60 and 59 years. The brothers were diagnosed at 41 and 50 years of age, respectively. Both patients exhibited an abnormally large area of substantia nigra echogenicity bilaterally when viewed with transcranial ultrasound. The abnormality was similar in both brothers despite one having a much longer disease duration than the other. These findings further highlight that transcranial ultrasound is not associated with severity of clinical symptoms, but it might assist in the diagnosis of PD provided that it is combined with other variables known to precede PD.
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: American Physiological Society
Date: 15-09-2015
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: Ovid Technologies (Wolters Kluwer Health)
Date: 12-2009
Publisher: Public Library of Science (PLoS)
Date: 29-12-2014
Publisher: American Physiological Society
Date: 09-2023
Abstract: This is the first time Australia-wide agreement has been reached on the core concepts of physiology with the Delphi method. Embedding of the core concepts will result in consistency in physiology curricula, improvements to teaching and learning, and benchmarking across Australian universities.
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: 31-05-2006
Publisher: Wiley
Date: 09-2003
Publisher: Springer Science and Business Media LLC
Date: 03-2002
DOI: 10.1007/S00421-001-0560-6
Abstract: The aim of this study was to characterise the effect of prolonged low doses of recombinant erythropoietin (r-HuEPO) on the responses to submaximal and maximal exercise. Volunteer recreational athletes ( n=21) were ided into three groups: r-HuEPO+intravenous iron (EPO+IV, n=7), r-HuEPO+oral iron (EPO+OR, n=9) and placebo ( n=5). During the 12 week study, r-HuEPO or saline injections were given three times a week for the first 8 weeks and for the final 4 weeks the subjects were monitored but no injections were administered. The r-HuEPO doses were 50 IU x kg(-1) body mass for 3 weeks and 20 IU x kg(-1) body mass for the next 5 weeks. An exercise test comprising three submaximal intensities and then increments to elicit maximal aerobic power (VO2max ) was conducted during weeks 0, 4, 8 and 12. During week 0, the mean intensity of the submaximal stages was 60%, 72% and 81%. Blood taken at rest was analysed twice a week for haematocrit (Hct). The relative increases in at weeks 4, 8 and 12 were 7.7%, 9.7% and 4.5%, respectively, for the EPO+IV group 6.0%, 4.7% and 3.1% for the EPO+OR group and -0.5%, -0.1% and -1.0% for the placebo group, where the improvements at week 12 for the EPO+IV and EPO+OR groups remained significantly above week 0 values. The Hct was significantly elevated by 0.06 and 0.07 units at week 3 in the EPO+IV and EPO+OR groups, respectively, and was stable during the 5 weeks of low-dose r-HuEPO. After 8 weeks of r-HuEPO use, plasma lactate concentration tended to be lower at exercise intensities ranging from 60% to 100%. This study confirmed the ability of low doses of r-HuEPO to maintain Hct and at elevated levels.
Publisher: Wiley
Date: 21-02-2005
Publisher: Wiley
Date: 07-2014
DOI: 10.1111/APHA.12327
Abstract: Few investigators have considered the possibility that skeletal muscles might contain thermosensitive elements capable of modifying thermoeffector responses. In this experiment, the temporal relationships between dynamic changes in deep-body and intramuscular temperatures and eccrine sweat secretion were explored during rhythmical and reproducible variations in heat production. Eight subjects performed semi-recumbent cycling (25 °C) at a constant load to first establish whole-body thermal and sudomotor steady states (35 min), followed by a 24-min block of sinusoidal workload variations (three, 8-min periods) and then returning to steady-state cycling (20 min). In idual oesophageal, mean skin and intramuscular (vastus lateralis) temperatures were independently cross-correlated with simultaneously measured forehead sweat rates to evaluate the possible thermal modulation of sudomotor activity. Both intramuscular and oesophageal temperatures showed strong correlations with sinusoidal variations in sweating with respective maximal cross-correlation coefficients of 0.807 (±0.044) and 0.845 (±0.035), but these were not different (P = 0.40). However, the phase delay between intramuscular temperature changes and sweat secretion was significantly shorter than the delay between oesophageal temperature and sweating [25.6 s (±12.6) vs. 46.9 s (±11.3) P = 0.03]. The temporal coupling of eccrine sweating to intramuscular temperature, combined with a shorter phase delay, was consistent with the presence of thermosensitive elements within skeletal muscles that appear to participate in the modulation of thermal sweating.
Publisher: Elsevier BV
Date: 03-2010
DOI: 10.1016/J.CLINPH.2009.11.089
Abstract: Ageing is accompanied by diminished practice-dependent plasticity. We investigated the effect of age on another plasticity inducing paradigm, repetitive transcranial magnetic stimulation (rTMS). Healthy young (n=15 25+/-4 years) and old (n=15 67+/-5 years) adults participated in two experiments. Motor evoked potentials (MEPs) were measured in the target muscle (first dorsal interosseus, FDI) and a remote muscle (abductor digiti minimi) during a set of single stimuli. Subjects then received real or sham inhibitory rTMS (intermittent subthreshold trains of 6Hz stimulation for 10min). MEPs were measured for 30min after rTMS. In young adults, MEPs in the target FDI muscle were approximately 15% smaller in the real rTMS experiment than in the sham rTMS experiment (P<0.026). In old adults, FDI MEP size did not differ between experiments. Advancing age is associated with reduced efficacy of inhibitory rTMS. This work has important implications for the potential therapeutic use of rTMS in stroke and neurological disease.
Publisher: Elsevier
Date: 2016
Publisher: Wiley
Date: 10-11-2022
DOI: 10.1002/JNR.25145
Abstract: Substantia nigra (SN) hyperechogenicity, viewed with transcranial ultrasound, is a risk marker for Parkinson's disease. We hypothesized that SN hyperechogenicity in healthy adults aged 50–70 years is associated with reduced short‐interval intracortical inhibition in primary motor cortex, and that the reduced intracortical inhibition is associated with neurochemical markers of activity in the pre‐supplementary motor area (pre‐SMA). Short‐interval intracortical inhibition and intracortical facilitation in primary motor cortex was assessed with paired‐pulse transcranial magnetic stimulation in 23 healthy adults with normal ( n = 14 61 ± 7 yrs) or abnormally enlarged (hyperechogenic n = 9 60 ± 6 yrs) area of SN echogenicity. Thirteen of these participants (7 SN− and 6 SN+) also underwent brain magnetic resonance spectroscopy to investigate pre‐SMA neurochemistry. There was no relationship between area of SN echogenicity and short‐interval intracortical inhibition in the ipsilateral primary motor cortex. There was a significant positive relationship, however, between area of echogenicity in the right SN and the magnitude of intracortical facilitation in the right (ipsilateral) primary motor cortex ( p = .005 multivariate regression), evidenced by the litude of the conditioned motor evoked potential (MEP) at the 10–12 ms interstimulus interval. This relationship was not present on the left side. Pre‐SMA glutamate did not predict primary motor cortex inhibition or facilitation. The results suggest that SN hyperechogenicity in healthy older adults may be associated with changes in excitability of motor cortical circuitry. The results advance understanding of brain changes in healthy older adults at risk of Parkinson's disease.
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: University of Otago Library
Date: 30-09-2022
Abstract: Introduction: Online learning has increased in popularity due to its perceived ability to improve access for students. With advancements in technology, traditional barriers such as location, time and space can be readily overcome. However, despite its popularity, there continues to be ongoing debate regarding its effectiveness. Methods: We searched commercially produced (six databases) and grey literature sources, limiting our search to humans and English language publications. Two reviewers independently screened the search results. Included studies were assessed for methodological quality assessment using the McMaster Critical Appraisal Tool for quantitative studies. Summarised data from the included studies were descriptively synthesised. Results: We identified a modest body of evidence (19 studies) that indicates that online learning interventions may have a positive impact on student engagement and academic performance for first-year allied health students. This finding should be considered with caution due to methodological concerns about the low-level evidence base arising from lack of adequate and representative s ling, lack of clarity and descriptions regarding the interventions utilised and lack of psychometrically sound outcome measures, just to name a few. Conclusions: There continues to remain key knowledge gaps in this field, such as who benefits the most, or the least, and the nature of any benefits and limitations, for which ongoing research is required.
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: 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: Elsevier BV
Date: 10-2023
Publisher: Elsevier BV
Date: 05-2012
DOI: 10.1016/J.CLINPH.2011.09.019
Abstract: The aim of our study was to use peristimulus frequencygram (PSF) constructed from single motor unit recordings to further characterise the responses evoked by low intensity TMS. Twelve healthy subjects (age 32 ± 11 years) received single-pulse TMS over the first dorsal interosseus (FDI) motor area during weak isometric index finger abduction. Several hundred stimuli were delivered at a frequency of ∼0.3 Hz and at an intensity of 79-110% of active motor threshold. FDI electromyogram (EMG) was recorded with surface and intramuscular fine wire electrodes. For single motor units, data analysis involved construction of a peristimulus time histogram (PSTH) and PSF. Surface EMG analysis involved signal averaging. Cumulative sums (CUSUMs) were calculated for SEMG, PSTH, and PSF data. Forty-five single motor units were identified. The average number of stimuli per unit was 201 ± 112. Characterisation of the response evoked by TMS differed with the use of SEMG, PSTH, and PSF CUSUMs. The duration of the EMG silence that follows the MEP during voluntary contraction was longer in the PSF than SEMG and PSTH. These findings highlight the importance of using both probability and frequency-based analysis when determining the duration of inhibitory events in peripheral recordings.
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: 09-2023
Abstract: This is the first attempt to unpack and validate the “structure and function” core concept in physiology with all Australian educators. We unpacked the renal system into themes with hierarchical levels, which were validated by an experienced team of Australian physiology educators. Our unpacking of the “structure and function” core concept provides a specific framework for educators to apply this important concept in physiology education.
Publisher: Wiley
Date: 17-10-2011
DOI: 10.1111/J.1460-9568.2011.07870.X
Abstract: Previous studies with transcranial magnetic stimulation (TMS) have shown that advancing age may influence plasticity induction in human motor cortex (M1), but these changes have been assessed with TMS-induced paradigms or simple motor tasks. The aim of this study was to examine changes in corticospinal excitability and intracortical inhibition as markers of corticomotor plasticity following complex motor training in young and old adults. Electromyographic recordings were obtained from the right first dorsal interosseous (FDI) muscle of 16 young (20-35 years) and 16 older (aged 60-75 years) adults before and after motor skill training. Motor training consisted of three 6-minute blocks of a complex visuomotor task that required matching the metacarpophalangeal (MCP) joint angle of the index finger using abduction-adduction movements. Single- and paired-pulse TMS over the left M1 was used to assess changes in right FDI motor-evoked potentials (MEPs) and short-interval intracortical inhibition (SICI) before and after each training block. Visuomotor tracking performance was diminished in old compared with young adults throughout training. However, improvement in tracking error was similar for young and old adults (7-24% increase in each training block). For young and old adults, motor training increased FDI MEP litude (≥ 20%) and reduced the magnitude of SICI (≥ 19%) after each visuomotor training block, reflecting use-dependent plasticity. However, no difference in corticomotor plasticity (change in MEP or SICI) was observed between young and old adults. Further studies are needed to identify the experimental or behavioral factors that might contribute to the maintenance of corticomotor plasticity in older adults.
Publisher: Elsevier
Date: 2010
Publisher: Public Library of Science (PLoS)
Date: 15-08-2019
Publisher: Elsevier BV
Date: 08-2012
DOI: 10.1016/J.CLINPH.2012.01.007
Abstract: To investigate tactile anisotropy on human lips. Spatial tactile acuity was assessed with a three-alternative, forced-choice grating orientation task. Circular probes with horizontal (parallel to lip), vertical (perpendicular to lip), or oblique (45° right of vertical) grooves and ridges of equal width were applied (n=60) to the midline of each lip. Participants (n=13) were asked to state the grating orientation whilst blindfolded. The percentage of correct responses was plotted as a function of the log gap width. Data were fitted with a four-parameter sigmoid function. Response bias was assessed (n=13) with application of a smooth polished Perspex probe. 65.5%, 71.5%, and 63.0% correct was adopted as the threshold estimate for the vertical, horizontal, and oblique orientations based on the measured response bias. Across orientations, the threshold on the upper lip (1.5 ± 0.9 mm) was significantly greater than on the lower lip (1.0 ± 0.7 mm P=0.006). However, there was no significant main effect of orientation or orientation-by-lip interaction on threshold. Tactile anisotropy is absent on human lips. The lack of anisotropy is surprising given that anisotropy is present on fingers and that afferent input and sensory processing for human lips and fingers share similarities.
Publisher: Hindawi Limited
Date: 2016
DOI: 10.1155/2016/9485079
Abstract: Little is known about the long-lasting effect of use of illicit stimulant drugs on learning of new motor skills. We hypothesised that abstinent in iduals with a history of primarily meth hetamine and ecstasy use would exhibit normal learning of a visuomotor tracking task compared to controls. The study involved three groups: abstinent stimulant users ( n = 21 27 ± 6 yrs) and two gender-matched control groups comprising nondrug users ( n = 16 22 ± 4 yrs) and cannabis users ( n = 16 23 ± 5 yrs). Motor learning was assessed with a three-minute visuomotor tracking task. Subjects were instructed to follow a moving target on a computer screen with movement of the index finger. Metacarpophalangeal joint angle and first dorsal interosseous electromyographic activity were recorded. Pattern matching was assessed by cross-correlation of the joint angle and target traces. Distance from the target (tracking error) was also calculated. Motor learning was evident in the visuomotor task. Pattern matching improved over time (cross-correlation coefficient) and tracking error decreased. However, task performance did not differ between the groups. The results suggest that learning of a new fine visuomotor skill is unchanged in in iduals with a history of illicit stimulant use.
Publisher: Frontiers Media SA
Date: 29-04-2015
Publisher: American Physiological Society
Date: 11-2012
DOI: 10.1152/JAPPLPHYSIOL.00718.2012
Abstract: Illicit use of stimulant drugs such as meth hetamine, ecstasy, and cocaine is a current and growing problem throughout the world. The aim of the current study was to investigate the long-term effect of illicit stimulant use on human motor cortical and corticospinal circuitry. We hypothesized that in iduals with a history of primarily meth hetamine and ecstasy use would exhibit altered corticospinal excitability and intracortical inhibition within motor cortex. The study involved 52 healthy adults (aged 26 ± 7 yr) comprising 26 abstinent stimulant users, 9 cannabis users, and 17 nondrug users. The experiment involved a routine urine drug screen, drug history questionnaire, neuropsychological assessment, and single- and paired-pulse transcranial magnetic stimulation (TMS) over motor cortex. EMG responses to stimulation [motor evoked potentials (MEPs)] were recorded from the contralateral first dorsal interosseus. At a given stimulus intensity, MEP area was significantly larger in abstinent stimulant users than in nondrug users during both relaxation ( P = 0.045) and muscle contraction ( P 0.001). MEP latency was also significantly longer in abstinent stimulant users ( P 0.009), and they exhibited significantly greater muscle activity during performance of a given task ( P = 0.004). However, resting motor threshold and the response to paired-pulse TMS were unaffected. The results suggest that abstinent stimulant users exhibit long-term changes in the excitability of motor cortical and corticospinal circuitry and muscle activity during movement. These changes may partly underlie anecdotal and objective reports of movement dysfunction in chronic stimulant users.
Publisher: Elsevier BV
Date: 09-2017
DOI: 10.1016/J.DRUGALCDEP.2017.05.017
Abstract: Despite evidence that cannabinoid receptors are located in movement-related brain regions (e.g., basal ganglia, cerebral cortex, and cerebellum), and that chronic cannabis use is associated with structural and functional brain changes, little is known about the long-term effect of cannabis use on human movement. The aim of the current study was to investigate balance and walking gait in adults with a history of cannabis use. We hypothesised that cannabis use is associated with subtle changes in gait and balance that are insufficient in magnitude for detection in a clinical setting. Cannabis users (n=22, 24±6years) and non-drug using controls (n=22, 25±8years) completed screening tests, a gait and balance test (with a motion capture system and in-built force platforms), and a clinical neurological examination of movement. Compared to controls, cannabis users exhibited significantly greater peak angular velocity of the knee (396±30 versus 426±50°/second, P=0.039), greater peak elbow flexion (53±12 versus 57±7°, P=0.038) and elbow range of motion (33±13 versus 36±10°, P=0.044), and reduced shoulder flexion (41±19 versus 26±16°, P=0.007) during walking gait. However, balance and neurological parameters did not significantly differ between the groups. The results suggest that history of cannabis use is associated with long-lasting changes in open-chain elements of walking gait, but the magnitude of change is not clinically detectable. Further research is required to investigate if the subtle gait changes observed in this population become more apparent with aging and increased cannabis use.
Publisher: Springer Science and Business Media LLC
Date: 11-04-2009
DOI: 10.1007/S00221-009-1791-8
Abstract: Repetitive transcranial magnetic stimulation (rTMS) can be used to study metaplasticity in human motor cortex. The term metaplasticity describes a phenomenon where the prior synaptic history of a pathway can affect the subsequent induction of long-term potentiation or depression. In the current study, we investigated metaplasticity in human motor cortex with the use of inhibitory continuous theta-burst stimulation (cTBS). cTBS involves short bursts of high frequency (50 Hz) rTMS applied every 200 ms for 40 s. In the first series of experiments, cTBS was primed with 10 min of intermittent 2 or 6 Hz rTMS. Subjects (n = 20) received priming stimulation at 70% of active motor threshold or 90% of resting motor threshold. In another series of experiments, cTBS was primed with excitatory intermittent theta-burst stimulation (iTBS). iTBS involves a 2 s train of theta-burst stimulation delivered every 10 s for 190 s. Stimuli were delivered over the first dorsal interosseus motor area.. The effect of cTBS alone and primed cTBS on motor cortical excitability was investigated by recording motor-evoked potentials (MEP) in the first dorsal interosseus following single-pulse TMS. MEP area in the cTBS alone condition was not significantly different from cTBS primed with 2 or 6 Hz rTMS. However, priming cTBS with iTBS suppressed MEP area to a greater extent than in cTBS alone. Our results provide further evidence of metaplasticity in human motor cortex when appropriate priming protocols are employed.
Publisher: Elsevier BV
Date: 04-2015
DOI: 10.1016/J.CLINPH.2014.07.010
Abstract: Restless legs syndrome, now called Willis-Ekbom Disease (RLS/WED), is a sensorimotor-related sleep disorder. Little is known of the effect of RLS/WED on motor function. The current study investigated upper limb function in RLS/WED patients. We hypothesised that RLS/WED patients exhibit subtle changes in tremor litude but normal dexterity and movement speed and rhythmicity compared to healthy controls. RLS/WED patients (n=17, 59 ± 7 years) with moderate disease and healthy controls (n=17, 58 ± 6 years) completed screening tests and five tasks including object manipulation, maximal pinch grip, flexion and extension of the index finger (tremor assessment), maximal finger tapping (movement speed and rhythmicity assessment), and the grooved pegboard test. Force, acceleration, and/or first dorsal interosseus EMG were recorded during four of the tasks. Task performance did not differ between groups. Learning was evident on tasks with repeated trials and the magnitude of learning did not differ between groups. Hand function, tremor, and task learning were unaffected in RLS/WED patients. Patients manipulated objects in a normal manner and exhibited normal movement speed, rhythmicity, and tremor. Further research is needed to assess other types of movement in RLS/WED patients to gain insight into the motor circuitry affected and the underlying pathophysiology.
Publisher: Wiley
Date: 2007
DOI: 10.1002/MUS.20708
Abstract: Patients with mitochondrial myopathies (MM) or myophosphorylase deficiency (McArdle's disease, McA) show impaired capacity for O(2) extraction, low maximal aerobic power, and reduced exercise tolerance. Non-invasive tools are needed to quantify the metabolic impairment. Six patients with MM, 6 with McA, 25 with symptoms of metabolic myopathy but negative biopsy (patient-controls, P-CTRL) and 20 controls (CTRL) underwent an incremental cycloergometric test. Pulmonary O(2) uptake (VO(2)) and vastus lateralis oxygenation indices (by near-infrared spectroscopy, NIRS) were determined. Concentration changes of deoxygenated hemoglobin and myoglobin (Delta[deoxy(Hb + Mb)]) were considered an index of O(2) extraction. Delta[deoxy(Hb + Mb)] peak (percent limb ischemia) was lower in MM (25.3 +/- 12.0%) and McA (18.7 +/- 7.3) than in P-CTRL (62.4 +/- 3.9) and CTRL (71.3 +/- 3.9) subjects. VO(2) peak and Delta[deoxy(Hb + Mb)] peak were linearly related (r(2) = 0.83). In these patients, NIRS is a tool to detect and quantify non-invasively the metabolic impairment, which may be useful in the follow-up of patients and in the assessment of therapies and interventions.
Publisher: Wiley
Date: 29-10-2012
DOI: 10.1111/EJN.12023
Abstract: Abnormally large tremor during movement is a symptom of many movement disorders and significantly impairs activities of daily living. The aim of this study was to investigate whether repetitive magnetic brain stimulation (rTMS) can reduce tremor size during human movement. We hypothesised that inhibitory rTMS over motor cortex would reduce tremor size during subsequent movement. The study involved 26 healthy young adults (21 ± 2 years) and began with application of single TMS stimuli to measure baseline corticospinal excitability. The response to stimulation was recorded in hand muscles with electromyography. Subjects then performed a 3-min task to measure baseline tremor during movement. This involved matching index finger position with a moving target on a computer screen. Tremor was recorded with an accelerometer on the fingernail. Finger acceleration was analysed with fast-Fourier transform to quantify tremor in the physiological range (7.8-12.2 Hz). Subjects then received 10 min of real (n = 13) or sham (n = 13) inhibitory rTMS. Tremor and corticospinal excitability were then remeasured. Real rTMS significantly decreased corticospinal excitability by ~30% (P = 0.022) and increased tremor size during movement by ~120% (P = 0.047) relative to sham rTMS. However, the direction of tremor change was opposite to that hypothesised for inhibitory rTMS. The results suggest that rTMS over human motor cortex can modulate action tremor and the level of corticospinal excitability may be important for setting the litude of action tremor in healthy young adults.
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: 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: American Physiological Society
Date: 12-2023
Abstract: A National Task force of 25 Australian physiology educators used the Delphi protocol to develop seven physiology core concepts which were agreed to nationally. The aim of the current study was to unpack the 'Physiological Adaptation' core concept with the descriptor 'Organisms adjust and adapt to acute and chronic changes in the internal and external environments across the lifespan'. This core concept was unpacked by three Task force members and a facilitator into four themes and nine subthemes that encompass the role of stressors and disturbed homeostasis in adaptation, and the capacity for, and the nature of, the Physiological Adaptation. Twenty-two Task force members then provided feedback and rated the themes and subthemes for level of importance and difficulty for students to learn via an online survey using a 5-point Likert scale. Seventeen respondents completed all survey questions. For all themes/subthemes, importance was rated 1 (essential) or 2 (important n=17, means ±SD ranged from 1.1±0.3 to 2.2±0.9) and difficulty was rated 3 (moderately difficult n=17, means ranged from 2.9±0.7 to 3.4±0.9). Subtle differences in the proportion of importance scores (n=17: Fishers exact p=0.004, ANOVA F 12,220 =2.630, p=0.003 n=22: Fishers exact p=0.002, ANOVA F 12,281 =2.743, p .001), but not difficulty scores, were observed between themes/subthemes, and free-text feedback was minor. The results suggest successful unpacking of the Physiological Adaptation core concept. The themes and subthemes can inform the design of learning outcomes, assessment, and teaching and learning activities that have commonality and consistency across curricula.
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: Springer Science and Business Media LLC
Date: 12-12-2018
DOI: 10.1007/S00702-017-1822-8
Abstract: Upper limb function was investigated in children with ADHD using objective methods. We hypothesised that children with ADHD exhibit abnormal dexterity, force application during manipulation of a novel object, and movement rhythmicity. Two groups of age- and gender-matched children were investigated: 35 typically developing children (controls, 10.5 ± 0.4 years, 32M-3F) and 29 children (11.5 ± 0.5 years, 27M-2F) with formally diagnosed ADHD according to DSM-IV-TR criteria. Participants underwent a series of screening tests and tests of upper limb function while "off" medication. Objective quantification of upper limb function involved measurement of force during a grip and lift task, maximal finger tapping task, and maximal pinch grip. Acceleration at the index finger was also measured during rest, flexion and extension, and a postural task to quantify tremor. The Movement Assessment Battery for Children-2 (MABC-2) was also administered. Significant between-group differences were observed in movement rhythmicity, manipulation of a novel object, and performance of the MABC-2 dexterity and aiming and catching components. Children with ADHD lifted a novel object using a lower grip force (P = 0.036), and held the object with a more variable grip force (P = 0.003), than controls. Rhythmicity of finger tapping (P = 0.008) and performance on the dexterity (P = 0.007) and aiming and catching (P = 0.042) components of the MABC-2 were also significantly poorer in the ADHD group than controls. Movement speed, maximum pinch grip strength, and tremor were unaffected. The results of the study show for the first time that ADHD is associated with deficits in multiple, but not all domains of upper limb function.
Publisher: American Physiological Society
Date: 09-2023
Abstract: The homeostasis core concept of physiology was defined and unpacked by an Australian team with the goal of constructing a resource that will improve learning and teaching of this core physiology concept in an Australian Higher Education context.
Publisher: Elsevier
Date: 2017
Publisher: American Physiological Society
Date: 09-2023
Abstract: This article proposes the inclusion of a core concept regarding “integration” into physiology-based curricula, with the descriptor “cells, tissues, organs, and organ systems interact to create and sustain life.” This concept expands prior knowledge and applies physiological understanding to real-world scenarios and introduces contexts such as medications, diseases, and aging to the student learning experience. To comprehend the topics within the Integration core concept, students will need to apply learned material from earlier semesters.
Publisher: Elsevier BV
Date: 2019
Publisher: Elsevier BV
Date: 05-2010
DOI: 10.1016/J.NEUROIMAGE.2010.01.088
Abstract: The aim of our study was to investigate the relation between substantia nigra (SN) echomorphology and indices of motor cortex excitability. Nigral hyperechogenicity in healthy in iduals is thought to represent an SN abnormality or predisposition to Parkinson's disease (PD) and its prevalence is greater in the very old. Our study involved 20 old healthy subjects (aged 72-84 years) known to have normal (n=10) or abnormal (n=10) SN echomorphology. All were in good health with no overt neurological signs. SN morphology was assessed with transcranial sonography through the pre-auricular bone window. Motor cortical excitability and intracortical inhibition were assessed with transcranial magnetic stimulation (TMS) over the first dorsal interosseus motor area. Single stimuli were delivered during relaxation and voluntary contraction and paired stimuli were delivered during relaxation. Each cortical hemisphere was analysed separately. The response to single-pulse TMS (in motor cortex ipsilateral to the target SN) did not differ between groups. However, a significant difference between groups was observed in the paired pulse paradigm (conditioning stimulus intensity: 70% resting motor threshold interstimulus interval: 2 ms). The conditioned motor evoked potential litude was significantly larger ipsilateral to the hyperechogenic SN than in controls (P=0.014). Thus, healthy subjects with SN hyperechogenicity exhibit significantly less intracortical inhibition within the motor cortex than subjects with normal echomorphology. Decreased intracortical inhibition is also observed in PD patients. This study provides further evidence that SN hyperechogenicity in healthy in iduals is associated with changes characteristic of PD supporting a role for this feature as a vulnerability marker or state marker for subtle nigral dopaminergic dysfunction.
Publisher: Oxford University Press (OUP)
Date: 30-04-2008
Publisher: Elsevier BV
Date: 12-2019
DOI: 10.1016/J.DRUGALCDEP.2019.107595
Abstract: Illicit stimulant use is associated with long-lasting changes in movement and movement-related brain regions. The aim of our study was to investigate the prevalence of movement dysfunction in this population. We hypothesized that prevalence of self-reported movement dysfunction is higher among stimulant users than non-stimulant users. Three groups of adults completed a survey containing questions about demographics, health, drug use, and movement. The groups consisted of ecstasy users with no history of meth hetamine use (ecstasy group, n = 190, 20 ± 3 yrs.), meth hetamine users (meth hetamine group, n = 331, 23 ± 5 yrs.), and non-stimulant users (control group, n = 228, 25 ± 8 yrs.). Movement data was analyzed with logistic regression. In the unadjusted logistic regression model, group had a significant effect on fine hand control, tremor, and voice/speech questions, but not on other movement domain questions. The prevalence of tremor and abnormal fine hand control was significantly higher in the ecstasy and meth hetamine groups than in the control group (p < 0.018), and changes in voice/speech was more prevalent in the ecstasy group than in the control group (p = 0.015). Age and use of cannabis and hallucinogens were confounding variables. However, inspection of chi-square tables suggests that the effect of these parameters on the movement data is likely to be minor. The prevalence of self-reported tremor and changes in fine hand control and voice/speech is significantly higher in stimulant users than in non-stimulant users. Inclusion of these common and noticeable changes in body function may aid public health c aigns that target prevention or harm minimization.
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.
No related grants have been discovered for Gabrielle Todd.