ARDC Research Link Australia

Publication

Deceleration affects anticipatory and reactive components of triggered postural responses

Publisher: Springer Science and Business Media LLC

Date: 23-07-2005

Abstract: Understanding the physiological and psychological factors that contribute to healthy and pathological balance control in man has been made difficult by the confounding effects of the perturbations used to test balance reactions. The present study examined how postural responses were influenced by the acceleration-deceleration interval of an unexpected horizontal translation. Twelve adult males maintained balance during unexpected forward and backward surface translations with two different acceleration-deceleration intervals and presentation orders (serial or random). "SHORT" perturbations consisted of an initial acceleration (peak acceleration 1.3 m s(-2) duration 300 ms) followed 100 ms later by a deceleration. "LONG" perturbations had the same acceleration as SHORT perturbations, followed by a 2-s interval of constant velocity before deceleration. Surface and intra-muscular electromyography (EMG) from the leg, trunk, and shoulder muscles were recorded along with motion and force plate data. LONG perturbations induced larger trunk displacements compared to SHORT perturbations when presented randomly and larger EMG responses in proximal and distal muscles during later (500-800 ms) response intervals. During SHORT perturbations, activity in some antagonist muscles was found to be associated with deceleration and not the initial acceleration of the support surface. When predictable, SHORT perturbations facilitated the use of anticipatory mechanisms to attenuate early (100-400 ms) EMG response litudes, ankle torque change and trunk displacement. In contrast, LONG perturbations, without an early deceleration effect, did not facilitate anticipatory changes when presented in a predictable order. Therefore, perturbations with a short acceleration-deceleration interval can influence triggered postural responses through reactive effects and, when predictable with repeated exposure, through anticipatory mechanisms.

Publication

INTRA-ABDOMINAL PRESSURE AND PATTERNS OF ABDOMINAL MUSCLE ACTIVATION IN ISOMETRIC TRUNK FLEXION AND EXTENSION

Publisher: Elsevier BV

Date: 1989

DOI: 10.1016/0021-9290(89)90155-3

Publication

Proprioceptive neuromuscular facilitation stretching - Mechanisms and clinical implications

Publisher: Springer Science and Business Media LLC

Date: 2006

DOI: 10.2165/00007256-200636110-00002

Abstract: Proprioceptive neuromuscular facilitation (PNF) stretching techniques are commonly used in the athletic and clinical environments to enhance both active and passive range of motion (ROM) with a view to optimising motor performance and rehabilitation. PNF stretching is positioned in the literature as the most effective stretching technique when the aim is to increase ROM, particularly in respect to short-term changes in ROM. With due consideration of the heterogeneity across the applied PNF stretching research, a summary of the findings suggests that an 'active' PNF stretching technique achieves the greatest gains in ROM, e.g. utilising a shortening contraction of the opposing muscle to place the target muscle on stretch, followed by a static contraction of the target muscle. The inclusion of a shortening contraction of the opposing muscle appears to have the greatest impact on enhancing ROM. When including a static contraction of the target muscle, this needs to be held for approximately 3 seconds at no more than 20% of a maximum voluntary contraction. The greatest changes in ROM generally occur after the first repetition and in order to achieve more lasting changes in ROM, PNF stretching needs to be performed once or twice per week. The superior changes in ROM that PNF stretching often produces compared with other stretching techniques has traditionally been attributed to autogenic and/or reciprocal inhibition, although the literature does not support this hypothesis. Instead, and in the absence of a biomechanical explanation, the contemporary view proposes that PNF stretching influences the point at which stretch is perceived or tolerated. The mechanism(s) underpinning the change in stretch perception or tolerance are not known, although pain modulation has been suggested.

Publication

Publisher: Ovid Technologies (Wolters Kluwer Health)

Date: 2018

DOI: 10.1249/MSS.0000000000001420

Publication

The influence of natural body sway on neuromuscular responses to an unpredictable surface translation

Publisher: Springer Science and Business Media LLC

Date: 17-03-2006

DOI: 10.1007/S00221-006-0414-X

Abstract: Previous research has shown that the postural configuration adopted by a subject, such as active leaning, influences the postural response to an unpredictable support surface translation. While those studies have examined large differences in postural conditions, it is of additional interest to examine the effects of naturally occurring changes in standing posture. Thus, it was hypothesized that the normal postural sway observed during quiet standing would affect the responses to an unpredictable support surface translation. Seventeen young adults stood quietly on a moveable platform and were perturbed in either the forward or backward direction when the location of the center of pressure (COP) was either 1.5 standard deviations anterior or posterior to the mean baseline COP signal. Postural responses, in the form of electromyographic (EMG) latencies and litudes, were recorded from lower limb and trunk muscles. When the location of the COP at the time of the translation was in the opposite, as compared to the same, direction as the upcoming translation, there was a significantly earlier onset of the antagonists (10-23%, i.e. 15-45 ms) and a greater EMG litude (14-39%) in four of the six recorded muscles. Stepping responses were most frequently observed during trials where the position of the COP was opposite to the direction of the translation. The results support the hypothesis that postural responses to unpredictable support surface translations are influenced by the normal movements of postural sway. The results may help to explain the large variability of postural responses found between past studies.

Publication

Recurrent inhibition of soleus alpha-motoneurons during a sustained submaximal plantar flexion

Publisher: Elsevier BV

Date: 08-1996

DOI: 10.1016/0924-980X(96)95670-2

Abstract: During 10 min of sustained isometric plantar flexion at 20% of maximal voluntary contraction, recurrent inhibition of soleus alpha-motoneurons was studied in 9 healthy subjects (age 22-37 years). Recurrent inhibition was brought about by a conditioning H-reflex and assessed by a test H-reflex delivered 10 ms later. The litude of the test H-reflex during the tenth minute of the contraction (16.9 +/- 13.2% of the maximal compound motor action potential) was significantly increased as compared to that during the first minute (9.8 +/- 7.6%), while the conditioning H-reflex remained unchanged. Concomitantly, muscle fatigue was evidenced by a significant increase in litude of the soleus electromyogram. The increase of the test-H-reflex litude implies that a decrease in recurrent inhibition occurred during the sustained submaximal contraction, which contrasts results from studies on maximal voluntary contractions. These results indicate a modulation of soleus Renshaw interneurons, which is likely to serve the purpose of optimising motor unit recruitment and firing rates of this muscle during a sustained submaximal contraction.

Publication

Bilateral tremor responses to unilateral loading and fatiguing muscle contractions.

Publisher: American Physiological Society

Date: 11-2008

DOI: 10.1152/JAPPLPHYSIOL.90586.2008

Abstract: This study investigated corticospinal-evoked responses in lower limb muscles during voluntary contractions at varying strengths. Similar investigations have been made on upper limb muscles, where evoked responses have been shown to increase up to ∼50% of maximal force and then decline. We elicited motor-evoked potentials (MEPs) and cervicomedullary motor-evoked potentials (CMEPs) in the soleus (Sol) and medial gastrocnemius (MG) muscles using magnetic stimulation over the motor cortex and cervicomedullary junction during voluntary plantar flexions with the torque ranging from 0 to 100% of a maximal voluntary contraction. Differences between the MEP and CMEP were also investigated to assess whether any changes were occurring at the cortical or spinal levels. In both Sol and MG, MEP and CMEP litudes [normalized to maximal M wave (M max )] showed an increase, followed by a plateau, over the greater part of the contraction range with responses increasing from ∼0.2 to ∼6% of M max for Sol and from ∼0.3 to ∼10% of M max for MG. Because both MEPs and CMEPs changed in a similar manner, the observed increase and lack of decrease at high force levels are likely related to underlying changes occurring at the spinal level. The evoked responses in the Sol and MG increase over a greater range of contraction strengths than for upper limb muscles, probably due to differences in the pattern of motor unit recruitment and rate coding for these muscles and the strength of the corticospinal input.

Publication

Date: 2016

DOI: 10.1242/JEB.142604

Abstract: Compliant tendons permit mechanically unfavourable fascicle dynamics during fixed-end contractions. The purpose of this study was to reduce the effective compliance of tendon and investigate how small reductions in active shortening affect twitch kinetics and contractile performance in response to a second stimulus. The series elastic element (SEE) of the human triceps surae (N=15) was effectively stiffened by applying a 55 ms rotation to the ankle, through a range of 5°, at the onset of twitch and doublet [interstimulus interval (ISI) of 80 ms] stimulation. Ultrasonography was employed to quantify lateral gastrocnemius and soleus fascicle lengths. Rotation increased twitch torque (40-75%), rate of torque development (RTD, 124-154%) and torque-time integral (TTI, 70-110%) relative to constant-length contractions at the initial and final joint positions, yet caused only modest reductions in shortening litude and velocity. The torque contribution of the second pulse increased when stimulation was preceded by rotation, a finding unable to be explained on the basis of fascicle length or SEE stiffness during contraction post-rotation. A further increase in torque contribution was not demonstrated, nor an increase in doublet TTI, when the second pulse was delivered during rotation and shortly after the initial pulse (ISI of 10 ms). The depressant effect of active shortening on subsequent torque generation suggests that compliant tendons, by affording large length changes, may limit torque summation. Our findings indicate that changes in tendon compliance shown to occur in response to resistance training or unloading are likely sufficient to considerably alter contractile performance, particularly maximal RTD.

Publication

Publisher: Ovid Technologies (Wolters Kluwer Health)

Date: 08-2016

DOI: 10.1249/MSS.0000000000000920

Publication

Increases in corticospinal responsiveness during a sustained submaximal plantar flexion

Publisher: American Physiological Society

Date: 07-2009

DOI: 10.1152/JAPPLPHYSIOL.91541.2008

Abstract: Studying the responsiveness of specific central nervous system pathways to electrical or magnetic stimulation can provide important information regarding fatigue processes in the central nervous system. We investigated the changes in corticospinal responsiveness during a sustained submaximal contraction of the triceps surae. Comparisons were made between the size of motor-evoked potentials (MEPs) elicited by motor cortical stimulation and cervicomedullary motor-evoked potentials (CMEPs) elicited by magnetic stimulation of the descending tracts to determine the site of any change in corticospinal responsiveness. Participants maintained an isometric contraction of triceps surae at 30% of maximal voluntary contraction (MVC) for as long as possible on two occasions. Stimulation was applied to the motor cortex or the cervicomedullary junction at 1-min intervals during contraction until task failure. Peripheral nerve stimulation was also applied to evoke maximal M waves (M max ) and a superimposed twitch. Additionally, MEPs and CMEPs were evoked during brief contractions at 80%, 90%, and 100% of MVC as a nonfatigue control. During the sustained contractions, MEP litude increased significantly in soleus (113%) and medial gastrocnemius (108%) muscles and, at task failure, matched MEP litude in the prefatigue MVC (∼20–25% M max ). In contrast, CMEP litude increased significantly in medial gastrocnemius (51%), but not in soleus (63%) muscle and, at task failure, was significantly smaller than during prefatigue MVC (5–6% M max vs. 11–13% M max ). The data indicate that cortical processes contribute substantially to the increase in corticospinal responsiveness during sustained submaximal contraction of triceps surae.

Publication

Galvanic vestibular stimulation alters the onset of motor unit discharge

Publisher: Wiley

Date: 2004

DOI: 10.1002/MUS.20074

Abstract: We have previously shown that galvanic vestibular stimulation (GVS) can modulate the litude of the passive soleus H-reflex. This study examined whether the response resulted from a general change in excitability of the motoneuron pool or a specific modulation of in idual motor units (MUs). Subjects performed slow isometric plantarflexor actions in a prone lying and kneeling position until the discharge of a single gastrocnemius MU was detected. During randomly selected trials, a 1-mA bipolar, binaural galvanic stimulus was triggered just prior to the start of plantarflexor activity. With the knee extended and the medial gastrocnemius (MG) at a long muscle length, GVS did not have an effect on MU activity. However, when the knee was flexed and the MG muscle was shortened, GVS significantly modified the onset of activation and the initial firing frequency of MUs. This may reflect a change in the gain of the presynaptic inhibitory mechanisms that act on the motoneuron pool once a muscle reaches a shortened, nonoptimal force-producing length. Thus, GVS may provide an important research tool for activating descending vestibulospinal pathways that act on lower-limb motoneurons and may be applied to test the integrity of the spinal cord.

Publication

Increasing step width reduces the requirements for subtalar joint moments and powers

Publisher: Elsevier BV

Date: 07-2019

DOI: 10.1016/J.JBIOMECH.2019.05.021

Abstract: The subtalar joint (STJ) contributes to the absorption and generation of mechanical energy (and power) during walking to maintain frontal plane stability. Previous observational studies have suggested that there may be a relationship between step width and STJ supination moment. This study directly tests the hypothesis that walking with a step width greater than preferred would reduce STJ moments, energy absorption, and power generation requirements, while increasing energy absorption at the hip during initial contact. Participants (n = 12, 7 females) were asked to walk on an instrumented treadmill at a constant velocity and cadence at a range of fixed step widths ranging from 0.1 to 0.4 times leg length (L). Walking at step widths greater than preferred (0.149 ± 0.04 L) reduced peak STJ moments at initial contact and propulsion which subsequently reduced the negative and positive work performed at the STJ. There was a 43% reduction in energy absorption (negative work) and approximately 30% decrease in positive work at the STJ as step width increased from 0.1 L to 0.4 L. An increase in energy absorption at the knee and hip was evident with an increase in step width during initial contact, although minimal mechanical changes were observed at the proximal joints during propulsion. These results suggest an increase in step width reduces the forces generated by muscles at the STJ across stance and is therefore likely to be beneficial in the prevention and treatment of their injuries. In terms of rehabilitation, the increase in mechanical costs occurring due to an increase in energy absorption by the hip and knee is of minimal concern.

Publication

ELECTROMYOGRAPHIC RESPONSES OF THE HUMAN TRICEPS SURAE AND FORCE TREMOR DURING SUSTAINED SUBMAXIMAL ISOMETRIC PLANTAR FLEXION

Publisher: Wiley

Date: 09-1994

DOI: 10.1111/J.1748-1716.1994.TB09786.X

Abstract: The objective was to investigate electromyographic activity (EMG) and isometric force tremor (IFT) changes during a sustained sub-maximal isometric contraction in two muscles acting upon the same joint but differing in muscle fibre composition. Surface and intra-muscular EMG activity from the gastrocnemius and soleus muscles and IFT were recorded during an exhausting isometric plantar flexion (30% of maximal voluntary contraction). Surface EMG litude (RMS) of both gastrocnemius and soleus muscles increased significantly over time. Gastrocnemius EMG RMS increased in a non-linear fashion while soleus EMG RMS increased linearly. A significant linear decrease of surface EMG mean power frequency (MPF) was observed over time for both muscles. The decrease in gastrocnemius MPF was significantly greater than that for soleus. Intra-muscular EMG results showed similar trends. Correlations of intramuscular EMG RMS and MPF with time were, however, characterized by lower correlation coefficients than those from the surface EMG. Isometric force tremor RMS significantly increased non-linearly with duration of contraction, while IFT MPF showed a significant linear decrease with time. Changes in surface EMG RMS were correlated to changes seen in IFT RMS, in particular, for the predominantly fast twitch gastrocnemius muscle. Correlation coefficients of surface EMG MPF and IFT MPF were lower than RMS correlations. The associated changes in IFT and EMG with fatigue indicate alterations in motor unit firing rate, recruitment and synchronization. The muscle specificity of the EMG and IFT changes suggests a coupling to muscle fibre type composition, although differences in the relative force contribution of each muscle could also affect the results.

Publication

Trunk muscle activity during different types of low weighted squat exercises in normal and forefoot standing conditions

Publisher: Informa UK Limited

Date: 04-08-2020

DOI: 10.1080/02640414.2020.1800358

Publication

Riders use their centre of mass to amplify crank power during non-seated cycling

Publisher: Center for Open Science

Date: 15-10-2019

DOI: 10.31236/OSF.IO/GHB24

Abstract: When cyclists ride off the saddle during climbing and sprinting, their centre of mass (CoM) appears to go through a rhythmic vertical oscillation during each crank cycle. Just like in walking and running, the pattern of CoM movement may have a significant impact on the mechanical power that needs to be generated and dissipated by muscle. To date, neither the CoM movement strategies during non-seated cycling, nor the limb mechanics that allow this phenomenon to occur, have been quantified. Here we estimate how much power can be contributed by a rider’s CoM at each instant during the crank cycle by combining a kinematic and kinetic approach to measure CoM movement and joint powers of fifteen participants riding in a non-seated posture at three in idualised power outputs (10%, 30%, and 50% of peak maximal power) and two different cadences (70 rpm and 120 rpm). Our analysis confirmed that vertical oscillations of the CoM occur within each crank cycle, with a peak-to-peak litude that increases significantly with power output and with decreasing cadence. Accordingly, the greatest peak-to-peak litude of CoM displacement (0.06 ± 0.01 m) and change in total mechanical energy (0.54 ± 0.12 J·kg-1) occurred under the combination of high power output and low cadence. Additionally, at the same combination of high power output and low cadence, we found that the peak rate of CoM energy loss (3.87 ± 0.93 W·kg-1) was equal to 18% of the peak crank power, which coincided with a near horizontal crank position (107 ± 10°). As a consequence, it appears that for a given power output, changes in CoM energy contribute to peak instantaneous power output at the crank, thus reducing the required muscular contribution. These findings suggest that riders can use the inertia of their CoM as a mechanical lifier during non-seated cycling, which has important implications for both rider and bicycle performance.

Publication

Publisher: Springer Science and Business Media LLC

Date: 04-1993

DOI: 10.1007/BF00237775

Publication

Residual force enhancement after lengthening is present during submaximal plantar flexion and dorsiflexion actions in humans

Publisher: American Physiological Society

Date: 2007

DOI: 10.1152/JAPPLPHYSIOL.00565.2006

Abstract: Stretch of an activated muscle causes a transient increase in force during the stretch and a sustained, residual force enhancement (RFE) after the stretch. The purpose of this study was to determine whether RFE is present in human muscles under physiologically relevant conditions (i.e., when stretches were applied within the working range of large postural leg muscles and under submaximal voluntary activation). Submaximal voluntary plantar flexion (PF v ) and dorsiflexion (DF v ) activation was maintained by providing direct visual feedback of the EMG from soleus or tibialis anterior, respectively. RFE was also examined during electrical stimulation of the plantar flexion muscles (PF s ). Constant-velocity stretches (15°/s) were applied through a range of motion of 15° using a custom-built ankle torque motor. The muscles remained active throughout the stretch and for at least 10 s after the stretch. In all three activation conditions, the stable joint torque measured 9–10 s after the stretch was greater than the isometric joint torque at the final joint angle. When expressed as a percentage of the isometric torque, RFE values were 7, 13, and 12% for PF v , PF s , DF v , respectively. These findings indicate that RFE is a characteristic of human skeletal muscle and can be observed during submaximal (25%) voluntary activation when stretches are applied on the ascending limb of the force-length curve. Although the underlying mechanisms are unclear, it appears that sarcomere popping and passive force enhancement are insufficient to explain the presence of RFE in these experiments.

Publication

The force-velocity relationship of the human soleus muscle during submaximal voluntary lengthening actions

Publisher: Springer Science and Business Media LLC

Date: 09-07-2003

DOI: 10.1007/S00421-003-0893-4

Abstract: In experiments on isolated animal muscle, the force produced during active lengthening contractions can be up to twice the isometric force, whereas in human experiments lengthening force shows only modest, if any, increase in force. The presence of synergist and antagonist muscle activation associated with human experiments in situ may partly account for the difference between animal and human studies. Therefore, this study aimed to quantify the force-velocity relationship of the human soleus muscle and assess the likelihood that co-activation of antagonist muscles was responsible for the inhibition of torque during submaximal voluntary plantar flexor efforts. Seven subjects performed submaximal voluntary lengthening, shortening(at angular, velocities of +5, -5, +15, -15 and +30, and -30 degrees s(-1)) and isometric plantar flexor efforts against an ankle torque motor. Angle-specific (90 degrees ) measures of plantar flexor torque plus surface and intramuscular electromyography from soleus, medial gastrocnemius and tibialis anterior were made. The level of activation (30% of maximal voluntary isometric effort) was maintained by providing direct visual feedback of the soleus electromyogram to the subject. In an attempt to isolate the contribution of soleus to the resultant plantar flexion torque, activation of the synergist and antagonist muscles were minimised by: (1) flexing the knee of the test limb, thereby minimising the activation of gastrocnemius, and (2) applying an anaesthetic block to the common peroneal nerve to eliminate activation of the primary antagonist muscle, tibialis anterior and the synergist muscles, peroneus longus and peroneus brevis. Plantar flexion torque decreased significantly ( P<0.05) after blocking the common peroneal nerve which was likely due to abolishing activation of the peroneal muscles which are synergists for plantar flexion. When normalised to the corresponding isometric value, the force-velocity relationship between pre- and post-block conditions was not different. In both conditions, plantar flexion torques during shortening actions were significantly less than the isometric torque and decreased at faster velocities. During lengthening actions, however, plantar flexion torques were not significantly different from isometric regardless of angular velocity. It was concluded that the apparent inhibition of lengthening torques during voluntary activation is not due to co-activation of antagonist muscles. Results are presented as mean (SEM).

Publication

Publisher: Elsevier BV

Date: 1989

DOI: 10.1016/0021-9290(89)90481-8

Publication

Quantification of muscle co-contraction using supersonic shear wave imaging

Publisher: Elsevier BV

Date: 02-2016

DOI: 10.1016/J.JBIOMECH.2015.12.039

Abstract: Muscle stiffness estimated using shear wave elastography can provide an index of in idual muscle force during isometric contraction and may therefore be a promising method for quantifying co-contraction. We estimated the shear modulus of the lateral gastrocnemius (LG) muscle using supersonic shear wave imaging and measured its myoelectrical activity using surface electromyography (sEMG) during graded isometric contractions of plantar flexion and dorsiflexion (n=7). During dorsiflexion, the average shear modulus was 26 ± 6 kPa at peak sEMG litude, which was significantly less (P=0.02) than that measured at the same sEMG level during plantar flexion (42 ± 10 kPa). The passive tension during contraction was estimated using the passive LG muscle shear modulus during a passive ankle rotation measured at an equivalent ankle angle to that measured during contraction. The passive shear modulus increased significantly (P<0.01) from the plantar flexed position (16 ± 5 kPa) to the dorsiflexed position (26 ± 9 kPa). Once this change in passive tension from joint rotation was accounted for, the average LG muscle shear modulus due to active contraction was significantly greater (P<0.01) during plantar flexion (26 ± 8 kPa) than at sEMG-matched levels of dorsiflexion (0 ± 4 kPa). The negligible shear modulus estimated during isometric dorsiflexion indicates negligible active force contribution by the LG muscle, despite measured sEMG activity of 19% of maximal voluntary plantar flexion contraction. This strongly suggests that the sEMG activity recorded from the LG muscle during isometric dorsiflexion was primarily due to cross-talk. However, it is clear that passive muscle tension changes can contribute to joint torque during isometric dorsiflexion.

Publication

Modulation of the soleus H-reflex during knee rotations is not consistent with muscle fascicle length changes

Publisher: Springer Science and Business Media LLC

Date: 11-01-2012

DOI: 10.1007/S00421-011-2302-8

Abstract: The purpose of this study was to examine whether passively rotating the knee would result in parallel or differential changes to the medial gastrocnemius (MG) and soleus (SOL) H-reflex litudes. Since passive knee rotation alters the muscle length of the MG, but not the SOL, it was hypothesized that the MG H-reflex would reflect the lengthening or shortening actions that occur during knee rotation, whereas the SOL H-reflex would remain unaltered. MG and SOL Hoffman reflexes (H-reflexes) were evoked with the knee joint held static at 10° or as the joint was passively flexed or extended past 10°. Ultrasound recordings were used to confirm whether the knee rotations altered MG but not SOL muscle fascicle lengths. In contrast to our hypothesis, results indicated that the MG and SOL H-reflexes were similarly affected during knee rotations, with both MG and SOL H(max):M(max) smaller during the knee extension than the knee flexion (33-43% reduction) and static (22-28% reduction) conditions. Parallel changes to the MG and SOL H-reflexes occurred despite a differential effect of knee rotation on muscle fascicle lengths. Whereas, MG muscle fascicles lengthened and shortened during knee extension and flexion, respectively, SOL fascicles length remained unchanged. Given the strong neural coupling between the MG and SOL motoneuron pools, the results highlight the difficulty in isolating specific variables (e.g., muscle length) when determining the modulatory influences on the triceps surae H-reflex litude.

Publication

Intrinsic foot muscles contribute to elastic energy storage and return in the human foot

Publisher: American Physiological Society

Date: 2019

DOI: 10.1152/JAPPLPHYSIOL.00736.2018

Abstract: The human foot is uniquely stiff to enable forward propulsion, yet also possesses sufficient elasticity to act as an energy store, recycling mechanical energy during locomotion. Historically, this dichotomous function has been attributed to the passive contribution of the plantar aponeurosis. However, recent evidence highlights the potential for muscles to modulate the energetic function of the foot actively. Here, we test the hypothesis that the central nervous system can actively control the foot’s energetic function, via activation of the muscles within the foot’s longitudinal arch. We used a custom-built loading apparatus to deliver cyclical loads to human feet in vivo, to deform the arch in a manner similar to that observed in locomotion. We recorded foot motion and forces, alongside muscle activation and ultrasound images from flexor digitorum brevis (FDB), an intrinsic foot muscle that spans the arch. When active, the FDB muscle fascicles contracted in an isometric manner, facilitating elastic energy storage in the tendon, in addition to the energy stored within the plantar aponeurosis. We propose that the human foot is akin to an active suspension system for the human body, with mechanical and energetic properties that can be actively controlled by the central nervous system. NEW & NOTEWORTHY The human foot is renowned for its ability to recycle mechanical energy during locomotion, contributing up to 17% of the energy required to power a stride. This mechanism has long been considered passive in nature, facilitated by the elastic ligaments within the arch of the foot. In this paper, we present the first direct evidence that the intrinsic foot muscles also contribute to elastic energy storage and return within the human foot. Isometric contraction of the flexor digitorum brevis muscle tissue facilitates tendon stretch and recoil during controlled loading of the foot. The significance of these muscles has been greatly debated by evolutionary biologists seeking to understand the origins of upright posture and gait, as well as applied and clinical scientists. The data we present here show a potential function for these muscles in contributing to the energetic function of the human foot.

Publication

BIOMECHANICAL EFFECTS OF OVERSPEED TREADMILL TRAINING ON SPRINT RUNNING

Publisher: Ovid Technologies (Wolters Kluwer Health)

Date: 02-1982

DOI: 10.1249/00005768-198202000-00201

Publication

Publisher: Elsevier BV

Date: 08-2004

DOI: 10.1016/J.NEULET.2004.05.044

Publication

Ultrasound reveals negligible cocontraction during isometric plantar flexion and dorsiflexion despite the presence of antagonist electromyographic activity

Publisher: American Physiological Society

Date: 15-05-2015

DOI: 10.1152/JAPPLPHYSIOL.00825.2014

Abstract: Because of the approximate linear relationship between muscle force and muscle activity, muscle forces are often estimated during maximal voluntary isometric contractions (MVICs) from torque and surface electromyography (sEMG) measurements. However, sEMG recordings from a target muscle may contain cross-talk originating from nearby muscles, which could lead to erroneous force estimates. Here we used ultrasound imaging to measure in vivo muscle fascicle length ( L f ) changes and sEMG to measure muscle activity of the tibialis anterior, medial gastrocnemius, lateral gastrocnemius, and soleus muscles during r MVICs in plantar and dorsiflexion directions ( n = 8). After correcting longitudinal L f changes for ankle rotation, the antagonist L f at peak antagonist root-mean-square (RMS) litude were significantly longer than the agonist L f at this sEMG-matched level. On average, L f shortened from resting length by 1.29 to 2.90 mm when muscles acted as agonists and lengthened from resting length by 0.43 to 1.16 mm when muscles acted as antagonists (depending on the muscle of interest). The lack of fascicle shortening when muscles acted as antagonists indicates that cocontraction was likely to be negligible, despite cocontraction as determined by sEMG of between 7 and 23% MVIC across all muscles. Different interelectrode distances (IEDs) over the plantar flexors revealed significantly higher antagonist RMS litudes for the 4-cm IEDs compared with the 2-cm IEDs, which further indicates that cross-talk was present. Consequently, investigators should be wary about performing agonist torque corrections for isometric plantar flexion and dorsiflexion based on the antagonist sEMG trace and predicted antagonist moment.

Publication

Tension regulation during lengthening and shortening actions of the human soleus muscle

Publisher: Springer Science and Business Media LLC

Date: 2000

DOI: 10.1007/S004210050057

Abstract: In the present study we investigated tension regulation in the human soleus (SOL) muscle during controlled lengthening and shortening actions. Eleven subjects performed plantar flexor efforts on an ankle torque motor through 30 degrees of ankle displacement (75 degrees -105 degrees internal ankle angle) at lengthening and shortening velocities of 5, 15 and 30 degrees. S(-1). To isolate the SOL from the remainder of the triceps surae, the subject's knee was flexed to 60 degrees during all trials. Voluntary plantar flexor efforts were performed under two test conditions: (1) maximal voluntary activation (MVA) of the SOL, and (2) constant submaximal voluntary activation (SVA) of the SOL. SVA trials were performed with direct visual feedback of the SOL electromyogram (EMG) at a level resulting in a torque output of 30% of isometric maximum. Angle-specific (90 degrees ankle angle) torque and EMG of the SOL, medial gastrocnemius (MG) and tibialis anterior (TA) were recorded. In seven subjects from the initial group, the test protocol was repeated under submaximal percutaneous electrical activation (SEA) of SOL (to 30% isometric maximal effort). Lengthening torques were significantly greater than shortening torques in all test conditions. Lengthening torques in MVA and SVA were independent of velocity and remained at the isometric level, whereas SEA torques were greater than isometric torques and increased at higher lengthening velocities. Shortening torques were lower than the isometric level for all conditions. However, whereas SVA and SEA torques decreased at higher velocities of shortening, MVA torques were independent of velocity. These results indicate velocity- and activation-type-specific tension regulation in the human SOL muscle.

Publication

Plantar- and dorsiflexor strength in prepubertal girls with juvenile idiopathic arthritis1,21No commercial party having a direct financial interest in the results of the research supporting this artic

Publisher: Elsevier BV

Date: 08-2004

DOI: 10.1016/J.APMR.2003.11.017

Publication

Doublet potentiation in the triceps surae is limited by series compliance and dynamic fascicle behavior

Publisher: American Physiological Society

Date: 10-2015

DOI: 10.1152/JAPPLPHYSIOL.00403.2015

Abstract: Activation of skeletal muscle twice in quick succession results in nonlinear force summation (i.e., doublet potentiation). The force contributed by a second activation is typically of augmented litude, longer in duration, and generated at a greater rate. The purpose of this study was to examine force summation in a muscle attached to a compliant tendon, where considerable internal shortening occurs during a fixed-end contraction. The triceps surae of 21 ( Experiment 1) and 9 ( Experiment 2) young adults were maximally activated with doublet stimulation of different interstimulus intervals (ISIs) (5-100 ms) at several muscle lengths. Ultrasound images acquired from lateral gastrocnemius and soleus muscles allowed quantification of dynamic fascicle behavior. Force summation was muscle length dependent. Force augmentation was limited to a short muscle length. Lateral gastrocnemius and soleus fascicles underwent large amounts of active shortening and achieved high velocities in response to doublet stimulation, dynamics unfavorable for force production. Summation litude and the sensitivity of summation to ISI were dramatically depressed in the triceps surae after comparison to muscles with less fixed-end compliance. We propose that the internal shortening permitted by high series compliance limited force augmentation by offsetting and/or interfering with activation and cross-bridge processes driving augmentation. High series compliance may also reduce the sensitivity of the summated response to ISI, an assertion supported by predictions from a Hill-type muscle model. These muscles may exhibit greater force augmentation during more accustomed stretch-shorten tasks (i.e., hopping), where the compliance of the Achilles tendon actually enables near-isometric fascicle behavior.

Publication

Publisher: Wiley

Date: 06-2014

DOI: 10.14814/PHY2.12044

Publication

Muscle spindles in human tibialis anterior encode muscle fascicle length changes

Publisher: American Physiological Society

Date: 04-2017

DOI: 10.1152/JN.00374.2016

Abstract: Muscle spindles provide exquisitely sensitive proprioceptive information regarding joint position and movement. Through passively driven length changes in the muscle-tendon unit (MTU), muscle spindles detect joint rotations because of their in-parallel mechanical linkage to muscle fascicles. In human microneurography studies, muscle fascicles are assumed to follow the MTU and, as such, fascicle length is not measured in such studies. However, under certain mechanical conditions, compliant structures can act to decouple the fascicles, and, therefore, the spindles, from the MTU. Such decoupling may reduce the fidelity by which muscle spindles encode joint position and movement. The aim of the present study was to measure, for the first time, both the changes in firing of single muscle spindle afferents and changes in muscle fascicle length in vivo from the tibialis anterior muscle (TA) during passive rotations about the ankle. Unitary recordings were made from 15 muscle spindle afferents supplying TA via a microelectrode inserted into the common peroneal nerve. Ultrasonography was used to measure the length of an in idual fascicle of TA. We saw a strong correlation between fascicle length and firing rate during passive ankle rotations of varying rates (0.1–0.5 Hz) and litudes (1–9°). In particular, we saw responses observed at relatively small changes in muscle length that highlight the sensitivity of the TA muscle to small length changes. This study is the first to measure spindle firing and fascicle dynamics in vivo and provides an experimental basis for further understanding the link between fascicle length, MTU length, and spindle firing patterns. NEW & NOTEWORTHY Muscle spindles are exquisitely sensitive to changes in muscle length, but recordings from human muscle spindle afferents are usually correlated with joint angle rather than muscle fascicle length. In this study, we monitored both muscle fascicle length and spindle firing from the human tibialis anterior muscle in vivo. Our findings are the first to measure these signals in vivo and provide an experimental basis for exploring this link further.

Publication

Muscle fascicle strains in human gastrocnemius during backward downhill walking

Publisher: American Physiological Society

Date: 06-2014

DOI: 10.1152/JAPPLPHYSIOL.01431.2012

Abstract: Extensive muscle damage can be induced in isolated muscle preparations by performing a small number of stretches during muscle activation. While typically these fiber strains are large and occur over long lengths, the extent of exercise-induced muscle damage (EIMD) observed in humans is normally less even when multiple high-force lengthening actions are performed. This apparent discrepancy may be due to differences in muscle fiber and tendon dynamics in vivo however, muscle and tendon strains have not been quantified during muscle-damaging exercise in humans. Ultrasound and an infrared motion analysis system were used to measure medial gastrocnemius fascicle length and lower limb kinematics while humans walked backward, downhill for 1 h (inducing muscle damage), and while they walked briefly forward on the flat (inducing no damage). Supramaximal tibial nerve stimulation, ultrasound, and an isokinetic dynamometer were used to quantify the fascicle length-torque relationship pre- and 2 h postexercise. Torque decreased ∼23%, and optimal fascicle length shifted rightward ∼10%, indicating that EIMD occurred during the damage protocol even though medial gastrocnemius fascicle stretch litude was relatively small (∼18% of optimal fascicle length) and occurred predominantly within the ascending limb and plateau region of the length-torque curve. Furthermore, tendon contribution to overall muscle-tendon unit stretch was ∼91%. The data suggest the compliant tendon plays a role in attenuating muscle fascicle strain during backward walking in humans, thus minimizing the extent of EIMD. As such, in situ or in vitro mechanisms of muscle damage may not be applicable to EIMD of the human gastrocnemius muscle.

Publication

The mechanical function of the tibialis posterior muscle and its tendon during locomotion

Publisher: Elsevier BV

Date: 10-2016

DOI: 10.1016/J.JBIOMECH.2016.08.006

Abstract: The tibialis posterior (TP) muscle is believed to provide mediolateral stability of the subtalar joint during the stance phase of walking as it actively lengthens to resist pronation at foot contact and then actively shortens later in stance to contribute to supination. Because of its anatomical structure of short muscle fibres and long series elastic tissue, we hypothesised that TP would be a strong candidate for energy storage and return. We investigated the potential elastic function of the TP muscle and tendon through simultaneous measurements of muscle fascicle length (ultrasound), muscle tendon unit length (musculoskeletal modelling) and muscle activation (intramuscular electromyography). In early stance, TP fascicles actively shortened as the entire muscle-tendon unit lengthened, resulting in the absorption of energy through stretch of the series elastic tissue. Energy stored in the tendinous tissue from early stance was maintained during mid-stance, although a small amount of energy may have been absorbed via minimal shortening in the series elastic elements and lengthening of TP fascicles. A significant amount of shortening occurred in both the fascicles and muscle-tendon unit in late stance, as the activation of TP decreased and power was generated. The majority of the shortening was attributable to shortening of the tendinous tissue. We conclude that the tendinous tissue of TP serves two primary functions during walking: 1) to buffer the stretch of its fascicles during early stance and 2) to enhance the efficiency of the TP through absorption and return of elastic strain energy.

Publication

The role of human ankle plantar flexor muscle-tendon interaction and architecture in maximal vertical jumping examined in vivo

Publisher: The Company of Biologists

Date: 2016

DOI: 10.1242/JEB.126854

Abstract: Humans utilise elastic tendons of lower limb muscles to store and return energy during walking, running and jumping. Anuran and insect species use skeletal structures and/or dynamics in conjunction with similarly compliant structures to lify muscle power output during jumping. We sought to examine if human jumpers use similar mechanisms to aid elastic energy usage in the plantar flexor muscles during maximal vertical jumping. Ten male athletes performed maximal vertical squat jumps. Three-dimensional motion capture and a musculoskeletal model were used to determine lower limb kinematics that were combined with ground reaction force data in an inverse dynamics analysis. B-mode ultrasound imaging of the lateral gastrocnemius (GAS) and soleus (SOL) muscles was used to measure muscle fascicle lengths and pennation angles during jumping. Our results highlighted that both GAS and SOL utilised stretch and recoil of their series elastic elements (SEE) in a catapult-like fashion, which likely serves to maximise ankle joint power. The resistance of supporting of body weight allowed initial stretch of both GAS and SOL SEE's. A proximal-to-distal sequence of joint moments and decreasing effective mechanical advantage (EMA) early in the extension phase of the jumping movement were observed. This facilitated a further stretch of the SEE of the biarticular GAS and delayed recoil of the SOL SEE. However, EMA did not increase late in the jump to aid recoil of elastic tissues.

Publication

Recruitment of single human low-threshold motor units with increasing loads at different muscle lengths

Publisher: Elsevier BV

Date: 06-2004

DOI: 10.1016/J.JELEKIN.2003.10.003

Publication

Publisher: American Physiological Society

Date: 19-10-2023

DOI: 10.1152/JAPPLPHYSIOL.00349.2023

Publication

Active regulation of longitudinal arch compression and recoil during walking and running

Publisher: The Royal Society

Date: 2015

DOI: 10.1098/RSIF.2014.1076

Abstract: The longitudinal arch (LA) of the human foot compresses and recoils in response to being cyclically loaded. This has typically been considered a passive process, however, it has recently been shown that the plantar intrinsic foot muscles have the capacity to actively assist in controlling LA motion. Here we tested the hypothesis that intrinsic foot muscles, abductor hallucis (AH), flexor digitorum brevis (FDB) and quadratus plantae (QP), actively lengthen and shorten during the stance phase of gait in response to loading of the foot. Nine participants walked at 1.25 m s −1 and ran at 2.78 and 3.89 m s −1 on a force-instrumented treadmill while foot and ankle kinematics were recorded according to a multisegment foot model. Muscle–tendon unit (MTU) lengths, determined from the foot kinematics, and intramuscular electromyography (EMG) signals were recorded from AH, FDB and QP. Peak EMG litude was determined during the stance phase for each participant at each gait velocity. All muscles underwent a process of slow active lengthening during LA compression, followed by a rapid shortening as the arch recoiled during the propulsive phase. Changes in MTU length and peak EMG increased significantly with increasing gait velocity for all muscles. This is the first in vivo evidence that the plantar intrinsic foot muscles function in parallel to the plantar aponeurosis, actively regulating the stiffness of the foot in response to the magnitude of forces encountered during locomotion. These muscles may therefore contribute to power absorption and generation at the foot, limit strain on the plantar aponeurosis and facilitate efficient foot ground force transmission.

Publication

THE ROLE OF THE ABDOMINAL MUSCULATURE IN THE ELEVATION OF THE INTRA-ABDOMINAL PRESSURE DURING SPECIFIED TASKS

Publisher: Informa UK Limited

Date: 10-1989

DOI: 10.1080/00140138908966893

Abstract: A series of standardized tasks, isometric trunk flexion and extension and maximal Valsalva manoeuvres, were used to evaluate the role of the abdominal musculature in developing an increased intra-abdominal pressure (IAP). Seven male subjects were measured for IAP, myoelectric activity of rectus abdominis (RA), obliquus externus and internus (OE and OI respectively), erector spinae (ES) and isometric trunk torque. IAPs in all experimental conditions were markedly greater than those that occurred while relaxed. In isometric trunk flexion, IAPs were increased with accompanying high levels of activity from the abdominal muscles. In contrast, little activity from the abdominal muscles occurred during isometric trunk extension, although levels of IAP were similar to those found in the isometric flexion condition. With maximal voluntary pressurization (Valsalva manoeuvre) slightly higher levels of IAP than those found in torque conditions were recorded, this pressure being produced with abdominal activities (OE and OI) less than one fourth their recorded maximum. When isometric torque tasks were added to the Valsalva manoeuvre, patterns of muscle activity (RA, OE, OI and ES) were significantly altered. For Valsalva with isometric trunk extension, activity from OE and OI was reduced while IAPs remained fairly constant. These findings indicate that in tasks where an IAP extension moment is warranted, abdominal pressure can be increased without the development of a large counter-moment produced by the dual action of the trunk flexors. Activation of other muscles such as the diaphragm and transversus abdominis is suggested as helping provide control over the level of IAP during controlled trunk tasks.

Andrew Cresswell

Researcher

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Publications

Deceleration affects anticipatory and reactive components of triggered postural responses

INTRA-ABDOMINAL PRESSURE AND PATTERNS OF ABDOMINAL MUSCLE ACTIVATION IN ISOMETRIC TRUNK FLEXION AND EXTENSION

Proprioceptive neuromuscular facilitation stretching - Mechanisms and clinical implications

Tension regulation of lengthening muscle actions: Implications for muscle strain injuries

Deconstructing the power resistance relationship for squats: A joint-level analysis

Differential control of abdominal muscles during multi-directional support-surface translations in man

The Influence of Foot-Strike Technique on the Neuromechanical Function of the Foot

The influence of natural body sway on neuromuscular responses to an unpredictable surface translation

Recurrent inhibition of soleus alpha-motoneurons during a sustained submaximal plantar flexion

Bilateral tremor responses to unilateral loading and fatiguing muscle contractions.

Discharge properties of abductor hallucis before, during, and after an isometric fatigue task

Effects of inspiratory muscle strength and inspiratory resistance on neck inspiratory muscle activation during controlled inspirations

Effects of running on human Achilles tendon length-Tension properties in the free and gastrocnemius components

Reliability and quality of statistical shape and deformation models constructed from optical foot scans

The energetic behaviour of the human foot across a range of running speeds

Cortical and Spinal Excitability during and after Lengthening Contractions of the Human Plantar Flexor Muscles Performed with Maximal Voluntary Effort

Three dimensional preparatory trunk motion precedes asymmetrical upper limb movement

TRUNK MUSCLE ACTIVATION IN A PERSON WITH CLINICALLY COMPLETE THORACIC SPINAL CORD INJURY

The immediate effect of physical activity on standing balance in healthy and balance-impaired older people

Ia-afferent input to motoneurons during shortening and lengthening muscle contractions in humans

Foot structure is significantly associated to subtalar joint kinetics and mechanical energetics

Perturbed upper limb movements cause short-latency postural responses in trunk muscles

Intervertebral Stiffness of the Spine Is Increased by Evoked Contraction of Transversus Abdominis and the Diaphragm: In Vivo Porcine Studies

Corticospinal contributions to lower limb muscle activity during cycling in humans

Recruitment of Discrete Regions of the Psoas Major and Quadratus Lumborum Muscles Is Changed in Specific Sitting Postures in Individuals With Recurrent Low Back Pain

The effect of different reference transducer positions on intra-abdominal pressure measurement: a multicenter analysis

Additional in-series compliance reduces muscle force summation and alters the time course of force relaxation during fixed-end contractions

Rock and roll: The influence of bicycle lean on the mechanics of non-seated cycling.

Corticospinal-evoked responses in lower limb muscles during voluntary contractions at varying strengths

Sustained Cycling Exercise Increases Intracortical Inhibition

Changes in direction-specific activity of psoas major and quadratus lumborum in people with recurring back pain differ between muscle regions and patient groups

Modulations in motor unit discharge are related to changes in fascicle length during isometric contractions

Temperature affects maximum H-reflex amplitude but not homosynaptic postactivation depression

In vivo fascicle length measurements via B-mode ultrasound imaging with single vs dual transducer arrangements

Dynamic postural stability is not impaired by moderate-intensity physical activity in healthy or balance-impaired older people

Changes in stepping response to lateral perturbations immediately following a single bout of physical activity.

Short-interval intracortical inhibition in knee extensors during locomotor cycling

Fine-wire recordings of flexor hallucis brevis motor units up to maximal voluntary contraction reveal a flexible, nonrigid mechanism for force control

Tibialis anterior tendinous tissue plays a key role in energy absorption during human walking

Vestibulospinal influences on lower limb motoneurons

Control of the triceps surae during the postural sway of quiet standing

Significance of peripheral afferent input to the alpha-motoneurone pool for enhancement of tremor during an isometric fatiguing contraction

An enhanced level of motor cortical excitability during the control of human standing

The Immediate Effect of Foot Orthoses on Subtalar Joint Mechanics and Energetics

Three-dimensional geometrical changes of the human tibialis anterior muscle and its central aponeurosis measured with three-dimensional ultrasound during isometric contractions

Changes in Regional Activity of the Psoas Major and Quadratus Lumborum With Voluntary Trunk and Hip Tasks and Different Spinal Curvatures in Sitting

The Mechanics of Seated and Nonseated Cycling at Very-High-Power Output: A Joint-Level Analysis

Corticospinal Responses to Sustained Locomotor Exercises: Moving Beyond Single-Joint Studies of Central Fatigue

The effect of knee flexion contracture following total knee arthroplasty on the energy cost of walking

Evidence for reduced efficacy of the Ia-pathway during shortening plantar flexions with increasing effort

Effects of series elastic compliance on muscle force summation and the rate of force rise

The efficacy of SMART Arm training early after stroke for stroke survivors with severe upper limb disability: a protocol for a randomised controlled trial

Recruitment of the plantar intrinsic foot muscles with increasing postural demand

The effect of muscle length on motor-unit recruitment during isometric plantar flexion in humans

A comparison of two Hill-type skeletal muscle models on the construction of medial gastrocnemius length-tension curves in humans in vivo

Linking Muscle Mechanics to the Metabolic Cost of Human Hopping

Rock and roll: The influence of bicycle lean on the mechanics of non-seated cycling

Anticipatory postural activity of the deep trunk muscles differs between anatomical regions based on their mechanical advantage.

Preparatory trunk motion accompanies rapid upper limb movement

Intrinsic foot muscles have the capacity to control deformation of the longitudinal arch

The Effect of Cadence on the Mechanics and Energetics of Constant Power Cycling

Protection from Muscle Damage in the Absence of Changes in Muscle Mechanical Behavior

Increases in corticospinal responsiveness during a sustained submaximal plantar flexion

Galvanic vestibular stimulation alters the onset of motor unit discharge

Increasing step width reduces the requirements for subtalar joint moments and powers

ELECTROMYOGRAPHIC RESPONSES OF THE HUMAN TRICEPS SURAE AND FORCE TREMOR DURING SUSTAINED SUBMAXIMAL ISOMETRIC PLANTAR FLEXION

Trunk muscle activity during different types of low weighted squat exercises in normal and forefoot standing conditions

Riders use their centre of mass to amplify crank power during non-seated cycling

Recruitment and rate coding organisation for soleus motor units across entire range of voluntary isometric plantar flexions

Central and peripheral contributions to fatigue in relation to level of activation during repeated maximal voluntary isometric plantar flexions

Muscle-Tendon length and force affect human tibialis anterior central aponeurosis stiffness in vivo

Age-related changes in postural responses revealed by support-surface translations with a long acceleration-deceleration interval