Length-tension properties of ankle muscles in chronic human spinal cord injury

Contracture, or loss of range of motion (ROM) of a joint, is a common clinical problem in individuals with spinal cord injury (SCI). In order to measure the possible contribution of changes in muscle length to the loss of ankle ROM, the active force vs. angle curves for the tibialis anterior (TA) and gastrocnemiussoleus (GS) were measured in 20 participants, 10 with SCI, and 10 gender and age matched, neurologically intact (NI) individuals. Electrical stimuli were applied to the TA and GS motor nerves at incremented angles of the entire ROM of the ankle and the resulting ankle and knee torques were measured using a multi-axis load cell. The muscle forces of the TA and GS were calculated from the torque measurements using estimates of their respective moment arms and the resulting forces were plotted against joint angle. The force–angle relation for the GS at the ankle (GSA) was significantly shifted into plantar flexion in SCI subjects, compared to NI controls (t-test, p<0.001). Similar results were obtained based upon the GS knee (GSK) force–angle measurements (p<0.05). Conversely, no significant shift in the force–angle relation was found for the TA (p=0.138). Differences in the passive ROM were consistent with the force–angle changes. The ROM in the dorsiflexion direction was significantly smaller in SCI subjects compared to NI controls (p<0.05) while the plantar flexion ROM was not significantly different (p=0.114). Based upon these results, we concluded that muscle shortening is an important component of contracture in SCI.     

Analysis of muscle activity and ankle joint movement during the side-hop test

Functional performance tests (FPTs) that consist of movements, such as hopping, landing, and cutting, provide useful measurements. Although some tests have been established for kinematic studies of the knee joint, very few tests have been established for the ankle joint. To use the FPT as a test battery for patients with an ankle sprain, it is necessary to document typical patterns of muscle activation and range of motion (ROM) of the ankle joint during FPTs. Therefore, the purpose of this study was to investigate the pattern of the ROM of the ankle inversion/eversion and the muscle activity of the peroneus longus muscle (PL) and the tibial anterior muscle (TA) in normal subjects during the side-hop test. To emphasize the characteristics of ROM and electromyography (EMG) at each phase, the side-hop tests were divided into 4 phases: lateral-hop contact phase (LC), lateral-hop flight phase (LF), medial hop contact phase (MC), and medial hop flight phase (MF), and the ROM of ankle inversion/eversion, a peak angle of ankle inversion, and Integral EMG (IEMG) of PL and TA compared among 4 phases. Fifteen male subjects with no symptoms of ankle joint problems participated in this research. The ROM of ankle inversion/eversion during the side-hop test was 27 ± 3.8° (mean ± SD), and there was a significant difference in the ROM of ankle inversion/eversion among 4 phases (p < 0.05). The phase in which the widest ROM was presented was the MF. A peak angle of the ankle inversion at MC was significantly greater than at LC and MF (p <0.05). A peak angle of the ankle inversion at LF was significantly greater than at LC and MF. The PL remained contracting with 50-160% of maximal voluntary contraction (MVC). The IEMGs of PL in both the contact phases were significantly greater than in both the flight phases (p < 0.05). In addition, the PL activity at LC was significantly greater than at MC. The TA remained contracting at 50-80% of MVC through the side-hop test. The IEMG of TA at both the contact phases was significantly greater than at 2 flight phases. However, there was no significant difference between LC and MF. Results of this study could be useful as basic data when evaluating the validity of the side-hop test for patients with ankle sprain.     

Modulation of spinal inhibitory reflexes depends on the frequency of transcutaneous electrical nerve stimulation in spastic stroke survivors

Neurophysiological studies in healthy subjects suggest that increased spinal inhibitory reflexes from the tibialis anterior (TA) muscle to the soleus (SOL) muscle might contribute to decreased spasticity. While 50?Hz is an effective frequency for transcutaneous electrical nerve stimulation (TENS) in healthy subjects, in stroke survivors, the effects of TENS on spinal reflex circuits and its appropriate frequency are not well known. We examined the effects of different frequencies of TENS on spinal inhibitory reflexes from the TA to SOL muscle in stroke survivors. Twenty chronic stroke survivors with ankle plantar flexor spasticity received 50-, 100-, or 200-Hz TENS over the deep peroneal nerve (DPN) of the affected lower limb for 30?min. Before and immediately after TENS, reciprocal Ia inhibition (RI) and presynaptic inhibition of the SOL alpha motor neuron (D1 inhibition) were assessed by adjusting the unconditioned H-reflex amplitude. Furthermore, during TENS, the time courses of spinal excitability and spinal inhibitory reflexes were assessed via the H-reflex, RI, and D1 inhibition. None of the TENS protocols affected mean RI, whereas D1 inhibition improved significantly following 200-Hz TENS. In a time-series comparison during TENS, repeated stimulation did not produce significant changes in the H-reflex, RI, or D1 inhibition regardless of frequency. These results suggest that the frequency-dependent effect of TENS on spinal reflexes only becomes apparent when RI and D1 inhibition are measured by adjusting the amplitude of the unconditioned H-reflex. However, 200-Hz TENS led to plasticity of synaptic transmission from the antagonist to spastic muscles in stroke survivors.     

Quantifying the effectiveness of the sustained muscle stretching treatments in stroke patients with ankle hypertonia.

Sustained muscle stretch (SMS) is commonly used to reduce hypertonia. The present study evaluates the effectiveness of three different SMS protocols, namely constant-angle, cyclic, and constant-torque stretching, in the immediate reducing of ankle hypertonia. Forty-seven hemiplegic subjects, 53.7+/-10.3 years old and 22.4+/-16.0 months after stroke, with hypertonic ankle joints were recruited to undergo three SMS applied to protocols treatment their hypertonic ankle joints using an integrated treatment/assessment system. The immediate post-treatment effectiveness of each stretching protocol was assessed by reference to the pre-treatment Modified Ashworth Scale (MAS), passive range of motion (ROM), and reactive torque measurement, from which the viscous-elastic components of the ankle joint were derived. All three SMS protocols successfully reduced MAS grade. Additionally, each stretching method yielded an increase in ankle ROM, from 9.7 degrees to 16 degrees , 9.6 degrees to 14.8 degrees , and 9.2 degrees to 18.3 degrees for the constant-angle, cyclic-stretching, constant-torque protocols, respectively, and reduction of the elastic and viscous properties of the ankle joint dorsiflexion (p<0.05). The changes in the ROM, elasticity, and viscosity were most pronounced in the case of the constant-torque stretching protocol. In addition to clinical scales, current biomechanical assessments indicate that three SMS protocols are all effective in reducing the immediate viscoelastic components of hypertonic ankle joints. Our quantitative analysis further shows that of the three treatment protocols, the constant-torque treatment is the most effective.     

Spasticity and spastic dystonia: the two faces of velocity-dependent hypertonia

BackgroundSpasticity and spastic dystonia are two separate phenomena of the upper motor neuron syndrome. Spasticity is clinically defined by velocity-dependent hypertonia and tendon jerk hyperreflexia due to the hyper-excitability of the stretch reflex. Spastic dystonia is the inability to relax a muscle leading to a spontaneous tonic contraction. Both spasticity and spastic dystonia are present in patients who are at rest; however, only patients with spasticity are actually able to kept their muscles relaxed prior to muscle stretch. The idea that has inspired the present work is that also in patients with spastic dystonia the stretch reflex is likely to be hyper-excitable. Therefore, velocity-dependent hypertonia could be mediated not only by spasticity, but also by spastic dystonia.MethodsTonic stretch reflexes in the rectus femoris muscle were evoked in 30 patients with multiple sclerosis showing velocity-dependent hypertonia of leg extensors and the habituation of the reflex was studied. Moreover, the capability of relax the muscle prior to muscle stretch (spastic dystonia) was also investigated.ResultsA tonic stretch reflex was evoked in all the enrolled patients. 73% of the patients were able to relax their rectus femoris muscle prior to stretch (spasticity). In the overwhelming majority of these patients, the tonic stretch reflex decreased during repeated stretches. In the remaining 27% of the subjects, the muscle was tonically activated prior to muscle stretch (spastic dystonia). In the patients in whom spastic dystonia progressively increased over the subsequent stretches (50% of the subjects with spastic dystonia), the habituation of the reflex was replaced by a progressive reflex facilitation.DiscussionThis study shows for the first time that velocity-dependent hypertonia can be caused by two distinct phenomena: spasticity and spastic dystonia. The habituation of the tonic stretch reflex, which is a typical feature of spasticity, is replaced by a reflex facilitation in the half of the subject with spastic dystonia. These preliminary findings suggest that differentiating the two types of velocity-dependent muscle hypertonia (spasticity and spastic dystonia) could be clinically relevant.     

Passive muscle mechanical properties of the medial gastrocnemius in young adults with spastic cerebral palsy

Individuals with spastic cerebral palsy (SCP) exhibit restricted joint range of motion and increased joint stiffness due to structural alterations of their muscles. Little is known about which muscle–tendon structures are responsible for these alterations. The aim of this study was to compare the passive mechanics of the ankle joint and medial gastrocnemius (MG) muscle in young adults with SCP and typically developed (TD) individuals. Nine ambulant SCP (17±2 years) and ten TD individuals (18±2 years) participated in the study. Physiological cross sectional area was estimated using freehand 3D ultrasound and found to be 37% lower in the SCP group. An isokinetic dynamometer rotated the ankle through its range while joint torque and ultrasound images of the MG muscle fascicles were simultaneously measured. Mean ankle stiffness was found to be 51% higher and mean MG fascicle strain 47% lower in the SCP group. Increased resistance to passive ankle dorsiflexion in SCP appears to be related to the inability of MG muscle fascicles to elongate with increased force.     

Short-term effects of thermotherapy for spasticity on tibial nerve F-waves in post-stroke patients

Thermotherapy is generally considered appropriate for post-stroke patients with spasticity, yet its acute antispastic effects have not been comprehensively investigated. F-wave parameters have been used to demonstrate changes in motor neuron excitability in spasticity and pharmacological antispastic therapy. The present study aimed to confirm the efficacy of thermotherapy for spasticity by evaluating alterations in F-wave parameters in ten male post-stroke patients with spastic hemiparesis (mean age: 49.0±15.0 years) and ten healthy male controls (mean age: 48.7±4.4 years). The subjects were immersed in water at 41°C for 10 min. Recordings were made over the abductor hallucis muscle, and antidromic stimulation was performed on the tibial nerve at the ankle. Twenty F-waves were recorded before, immediately after, and 30 min following thermotherapy for each subject. F-wave amplitude and F-wave/M-response ratio were determined. Changes in body temperature and surface-skin temperature were monitored simultaneously. The mean and maximum values of both F-wave parameters were higher on the affected side before thermotherapy. In the post-stroke patients, the mean and maximum values of both parameters were significantly reduced after thermotherapy (P<0.01). Hence, the antispastic effects of thermotherapy were indicated by decreased F-wave parameters. Body temperature was significantly increased both immediately after and 30 min after thermotherapy in all subjects. This appeared to play an important role in decreased spasticity. Surface-skin temperature increased immediately after thermotherapy in both groups and returned to baseline 30 min later. These findings demonstrate that thermotherapy is an effective nonpharmacological antispastic treatment that might facilitate stroke rehabilitation.     

Predictability of in vivo changes in pennation angle of human tibialis anterior muscle from rest to maximum isometric dorsiflexion

The aim of this study was to assess the predictability of in vivo, ultrasound-based changes in human tibialis anterior (TA) pennation angle from rest to maximum isometric dorsiflexion (MVC) using a planimetric model assuming constant thickness between aponeuroses and straight muscle fibres. Sagittal sonographs of TA were taken in six males at ankle angles of -15 degrees (dorsiflexion direction), 0 degrees (neutral position), + 15 (plantarflexion direction) and + 30 degrees both at rest and during dorsiflexor MVC trials performed on an isokinetic dynamometer. At all four ankle angles scans were taken from the TA proximal, central and distal regions. TA architecture did not differ (P > 0.05) neither between its two unipennate parts nor along the scanned regions over its length at a given ankle angle and state of contraction. Comparing MVC with rest at any given ankle angle, pennation angle was larger (62-71%, P < 0.01), fibre length smaller (37-40%, P < 0.01) and muscle thickness unchanged (P > 0.05). The model used estimated accurately (P > 0.05) changes in TA pennation angle occurring in the transition from rest to MVC and therefore its use is encouraged for estimating the isometric TA ankle moment and force generating capacity using musculoskeletal modelling.     

Characterization of the mechanical and neural components of spastic hypertonia with modified H reflex.

As the H reflex remains unable to assess mechanical changes intrinsic to a muscle, the aim of this study was to modify the H reflex techniques and to characterize the neural and mechanical components of muscle spasticity, relating the two components to clinical observations. Thirty-four patients featuring either a spinal-cord lesion (n=15) or stroke (n=19) and 23 neurologically normal subjects were recruited. Soleus H reflex and maximal M response (M(max)) were measured with electromyography and mechanomyography (MMG). The motoneuronal excitability was represented with the adjusted ratio of the H reflex to the M(max) (H/M(max)) and the ratio of the paired H reflexes (H(2)/H(1)). Muscle mechanical properties were characterized by the amplitude and median frequency of maximal M response recorded with MMG (MMG(Mmax)). The results showed that spastic patients exhibited a larger H/M(max), H(2)/H(1) and amplitude of MMG(Mmax) than the control group. H/M(max) and amplitude of MMG(Mmax) accounted for 55.7% of the variance in the Modified Ashworth Scale, the clinical hypertonia assessment. The amplitude of MMG(Mmax) correlated with functional impairments, as assessed with the Barthel index and Fugl-Meyer motor-assessment scale. It was concluded that spastic hypertonia involved an atypical increase in motoneuronal excitability and muscle mechanical properties, while impairment of functional performance and daily activity was attributable primarily to altered mechanical properties of a spastic muscle.     

A predictive model of moment-angle characteristics in human skeletal muscle: application and validation in muscles across the ankle joint

In the present work, a generic model for the prediction of moment-angle characteristics in individual human skeletal muscles is presented. The model's prediction is based on the equation M = V x Lo(-1)sigma c cos phi x d, where M, V, and Lo are the moment-generating potential of the muscle, the muscle volume and the optimal muscle fibre length, respectively, and sigma, phi and d are the stress-generating potential of the muscle fibres, their pennation angle and the tendon moment arm length, respectively, at any given joint angle. The input parameters V, Lo, sigma, phi and d can be measured or derived mechanistically. This eliminates the common problem of the necessity to estimate one or more of the input parameters in the model by fitting its outcome to experimental results often inappropriate for the function modelled. The model's output was validated by comparisons with the moment-angle characteristics of the gastrocnemius (GS) and tibialis anterior (TA) muscles in six men, determined experimentally using voluntary contractions at several combinations of ankle and knee joint angles for the GS muscle and electrical stimulation for the TA muscle. Although the model predicted realistically the pattern of moment-angle relationship in both muscles, it consistently overestimated the GS muscle M and consistently underestimated the TA muscle M, with the difference gradually increasing from dorsiflexion to plantarflexion in both cases. The average difference between predicted and measured M was 14% for the GS muscle and 10% for the TA muscle. Approximating the muscle fibres as a single sarcomere in both muscles and failing to achieve complete TA muscle activation by electrical stimulation may largely explain the differences between theory and experiment.     

Beneficial effects of footbaths in controlling spasticity after stroke

Footbaths are considered to provide beneficial thermal therapy for post-stroke patients with spasticity, but their anti-spastic effects have not been investigated comprehensively. The present study aimed to evaluate alterations in motor-neuron excitability using F-wave parameters in post-stroke patients with spastic hemiplegia. Subjects’ legs below the knee joint were immersed in water at 41°C and F-wave recordings were made over the abductor hallucis muscle before, immediately after, and 30 min after thermal treatment. Antidromic stimulation was performed on the tibial nerve at the ankle. Measurements included F-wave amplitude, F-wave/M-response ratio, changes in modified Ashworth scale (MAS), body temperature and surface-skin temperature. The mean values of both F-wave parameters were higher on the affected side before footbath treatment. In post-stroke patients, the mean values of F-wave parameters were significantly reduced after footbath treatment (P < 0.01). The anti-spastic effects of footbath treatment were indicated by decreased F-wave parameters, in parallel with decreases in MAS. Body temperature was significantly increased both immediately after, and 30 min following footbath treatment in both groups, which appeared to play an important role in decreased spasticity. Surface-skin temperature increased immediately after footbath treatment in both groups and returned to baseline 30 min later. These findings demonstrate that the use of footbaths is an effective nonpharmacological anti-spastic treatment that might facilitate stroke rehabilitation.     

Muscle activation of patients suffering from asymmetric ankle osteoarthritis during isometric contractions and level walking – A time–frequency analysis

Asymmetric osteoarthritis (OA) is a common type of OA in the ankle joint. OA also influences the muscles surrounding a joint, however, little is known about the muscle activation in asymmetric ankle OA. Therefore, the aim of this study was to characterize the patients’ muscle activation during isometric ankle torque measurements and level walking. Surface electromyography (EMG) was measured of gastrocnemius medialis (GM) and lateralis (GL), soleus (SO), tibialis anterior (TA), and peroneus longus (PL) in 12 healthy subjects and 12 ankle OA patients. To obtain time and frequency components of the EMG power a wavelet transformation was performed. Furthermore, entropy was introduced to characterize the homogeneity of the wavelet patterns.Patients produced lower plantar- and dorsiflexion torques and their TA wavelet spectrum was shifted towards lower frequencies. While walking, the patients’ muscles were active with a lower intensity and over a broader time–frequency region. In contrast to controls and varus OA patients, maximal GM activity of valgus OA patients lagged behind the activity of GL and SO. In both tasks, PL of the valgus patients contained more low frequency power. The results of this study will help to assess whether surgical interventions of ankle OA can reestablish the muscle activation patterns.     

In vivo passive mechanical properties of the human gastrocnemius muscle belly

The purpose of the present study was to determine the in vivo passive mechanical properties, including the length below the slack length, of the gastrocnemius muscle (GAS) belly in humans. Transverse ultrasound images of the medial head of the GAS were taken in 11 subjects during passive knee extension from 80 degrees to 5 degrees with a constant ankle joint angle of 10 degrees (0 degrees is the neutral ankle position: positive values for dorsiflexion). The change in passive ankle joint moment (Mp), which is produced only by the GAS length change, was also measured during passive knee extension. The onset of Mp during passive knee extension was found to be 43+/-8 degrees (mean+/-SD) when the baseline of the Mp was set at the average Mp in the range of 55-60 degrees where the Mp was almost constant (SD<0.03 Nm). At this onset, the muscle fascicle length of the GAS (Lf) was 46+/-7 mm (slack length; Lfs). Lf at 80 degrees was 6+/-4 mm (13+/-6%) less than the Lfs, and Lf at 5 degrees was 12+/-5 mm (27+/-11%) greater than the Lfs. The passive force-resisting compression of the GAS did not produce a dorsiflexion moment in the joint angle range adopted. The passive ankle joint moment increased linearly with Lf (coefficient of determination (R2)=0.85-0.96), and the slopes of the relationships between Lf and Mp, and between the relative Lf to Lfs and Mp were 0.093+/-0.038 Nm/mm and 0.043+/-0.021 Nm/%Lfs. The findings of the present study can be implemented in musculoskeletal modeling, which would provide a more accurate evaluation of the passive mechanical properties of muscle during movement.     

Adding weights to stretching exercise increases passive range of motion for healthy elderly

Stretching exercise is effective for increasing joint range of motion (ROM). However, the Surgeon General's Report and the American College of Sports Medicine cite a lack of studies identifying strategies capable of increasing the effectiveness of stretching exercise. This investigation evaluated adding modest weight (0.45-1.35 kg) to a stretching exercise routine (Body Recall [BR]) on joint ROM. Forty-three subjects ages 55-83 years participated in 1 of 2 training groups, BR, BR with weights (BR+W), or a control group (C). ROM was evaluated at the neck, shoulder, hip, knee, and ankle before and after 10 weeks of exercise. Using ANCOVA, significant differences (p < 0.01) were observed for right and left cervical rotation, hip extension, ankle dorsiflexion, ankle plantar flexion, and shoulder flexion. Post hoc analysis revealed that cervical rotation (left and right), hip extension, and ankle dorsiflexion for BR+W subjects differed significantly from BR and C (p < 0.01). Significant differences with shoulder flexion and ankle plantar flexion were found for both BR and BR+W in comparison to C (p < 0.01). Results indicate that addition of weights enhanced the effectiveness of stretching exercise for increasing joint ROM with 4 of the 6 selected measurements. Thus, a modest intensity exercise program that is within the reach of most elderly may significantly affect joint ROM and flexibility.     

Assessment of post-stroke elbow flexor spasticity in different forearm positions

Abstract

Purpose/Aim: There have been conflicting results regarding which muscle contribute most to the elbow spastic flexion deformity. This study aimed to investigate whether flexor spasticity of the elbow changed according to the position of the forearm, and to determine the muscle or muscles that contributed most to the elbow spastic flexion deformity by clinical examination.

Methods: This study is a single group, observational and cross-sectional study. Sixty patients were assessed for elbow flexor spasticity in different forearm positions (pronation, neutral and supination) with Modified Tardieu Scale. The primary outcome measure was a domain of the Modified Tardieu Scale, the dynamic component of spasticity (spasticity angle).

Results: In general, there was a significant difference between forearm positions regarding spasticity angle (p?<?.001). In pairwise comparisons, median spasticity angles in pronation (70 degrees) and neutral position (60 degrees) were significantly higher than those in supination (57.5 degrees) (adjusted p?<?.001 and adjusted p?=?.003, respectively). However, median spasticity angle in pronation did not differ significantly from those in neutral position in favour of pronation (adjusted p?=?.274).

Conclusions: The severity of spasticity changes according to the elbow position which suggests that the magnitude of contribution of each elbow flexor muscle to spastic elbow deformity is different. Reduction of spasticity from pronation to supination leads us to consider brachialis as the most spastic muscle. Since biceps was suggested to be the least spastic muscle in this study, and also to avoid spastic pronation deformity of the forearm, it should be rethought before performing chemodenervation into biceps muscle.     

Influence of low muscle activation levels on the ankle torque and muscle shear modulus during plantar flexor stretching

During stretching studies, surface electromyography (sEMG) is used to ensure the passive state of the muscle, for the characterization of passive muscle mechanical properties. Different thresholds (1%, 2% or 5% of maximal) are indifferently used to set “passive state”. This study aimed to investigate the effects of a slight activity on the joint and muscle mechanical properties during stretching.The joint torque and muscle shear modulus of the triceps surae muscles were measured in fifteen healthy volunteers during ankle dorsiflexions: (i) in a “fully relaxed” state, (ii) during active conditions where participants were asked to produce an sEMG amplitude of 1%, 2% or 5% of their maximal sEMG amplitude of the triceps surae. The 1% condition was the only that did not result in significant differences in joint torque or shear modulus compared to the relaxed condition. In the 2% condition, increases in joint torque were found at 80% of the maximal angle in dorsiflexion, and in the shear modulus of gastrocnemius medialis and gastrocnemius lateralis at the maximal angle in dorsiflexion. During the 5% condition, joint torque and the shear modulus of gastrocnemius medialis were higher than during relaxed condition at angles larger than 40% of maximal angle in dorsiflexion. The results provide new insights on the thresholds that should be considered for the design of stretching studies. A threshold of 1% seems much more appropriate than a 2% or 5% threshold in healthy participants. Further studies are required to define similar thresholds for patients.     

Effects of fatiguing unilateral plantar flexions on corticospinal and transcallosal inhibition in the primary motor hand area

Background

Corticospinal excitability of the primary motor cortex (M1) representing the hand muscle is depressed by bilateral lower limb muscle fatigue. The effects of fatiguing unilateral lower limb contraction on corticospinal excitability and transcallosal inhibition in the M1 hand areas remain unclear. The purpose of this study was to determine the effects of fatiguing unilateral plantar flexions on corticospinal excitability in the M1 hand areas and transcallosal inhibition originated from the M1 hand area contralateral to the fatigued ankle.

Methods

Ten healthy volunteers (26.2 ± 3.8 years) participated in the study. Using transcranial magnetic stimulation, we examined motor evoked potentials (MEPs) and interhemispheric inhibition (IHI) recorded from resting first dorsal interosseous (FDI) muscles before, immediately after, and 10 min after fatiguing unilateral lower limb muscle contraction, which was consisted of 40 unilateral maximal isometric plantar flexions intermittently with a 2-s contraction followed by 1 s of rest.

Results

We demonstrated no significant changes in MEPs in the FDI muscle ipsilateral to the fatigued ankle and decrease in IHI from the M1 hand area contralateral to the fatigued ankle to the ipsilateral M1 hand area after the fatiguing contraction. MEPs in the FDI muscle contralateral to the fatigued ankle were increased after the fatiguing contraction.

Conclusions

These results suggest that fatiguing unilateral lower limb muscle contraction differently influences corticospinal excitability of the contralateral M1 hand area and IHI from the contralateral M1 hand area to the ipsilateral M1 hand area. Although fatiguing unilateral lower limb muscle contraction increases corticospinal excitability of the ipsilateral M1 hand area, the increased corticospinal excitability is not associated with the decreased IHI.     

In vivo human tendinous tissue stretch upon maximum muscle force generation

In the present study, we examined the hypothesis that stretch of tendinous tissue in the human tibialis anterior (TA) muscle-tendon unit upon isometric dorsiflexion maximum voluntary contraction (MVC) varies along the entire tendinous component length. Ultrasound-based measurements of the excursions of the TA tendon origin and proximal end of the TA central aponeurosis were taken in the transition from rest to MVC in six men. Subtracting the TA tendon origin excursion from the excursion of the aponeurosis proximal end, the aponeurosis excursion was estimated. Estimation of the aponeurosis proximal region excursion was obtained subtracting the excursion of the insertion point of a central region fascicle on the aponeurosis from the whole aponeurosis excursion. Subtracting tendon excursion from the excursion of the central fascicle insertion point, the aponeurosis distal region excursion was estimated. Strain values were calculated dividing the excursions obtained by the original resting lengths. All excursions and lengths were measured in the mid-longitudinal axis of the TA muscle-tendon unit at the neutral anatomical ankle position. Tendon excursion and strain were 0.5+/-0. 08 cm (mean+/-SE) and 3.1+/-0.2%, respectively. Aponeurosis excursion and strain were 1.1+/-0.15 cm and 6.5+/-0.6%, respectively. Aponeurosis distal region excursion and strain were 0.3+/-0.05 cm and 3.5+/-0.3%, respectively. Aponeurosis proximal region excursion and strain were 0.8+/-0.12 cm and 9.2+/-1%, respectively. Aponeurosis excursion and strain were larger by 110-120% (P<0.05) compared with tendon. Aponeurosis proximal region excursion and strain were larger by 165-170% (P<0.05) compared with aponeurosis distal region. These findings are in line with results from in vitro animal material testing and have important implications for theoretical models of muscle function.