Tibialis Anterior Contraction Research Articles

The crural interosseous membrane re-visited: Part II, new biomechanical concepts

Demonstrate movement of the Interosseous Membrane (IM) when tensile loading was applied to the Tibialis Anterior (TA) and Tibialis Posterior (TP). Postulate new roles for IM in running. Nine IMs were assessed by 2 examiners. Dissections exposed the TA and TP. Posterior IM was palpated under TP as tensile loading of TA applied. Anterior IM was palpated under TA, as tensile loading of TP applied. Tensile loading was measured via a spring scale attached to distal tendons of TA and TP. TA tensile loading caused movement of IM anteriorly. TP tensile loading caused movement of IM posteriorly. T-test revealed no statistically significant difference between two examiners. The IM moves when TA and TP muscles undergo tensile loading. Rapid TA contraction during running pulls on the IM, pre-stretching TP and resulting in a forceful TP contraction. The IM is an important factor in pre-stretching of TA and TP. Nerve endings found in IM in our previous publication can increase afferent signal input and coordinate muscle activation of anterior and posterior IM muscles; IM acts as both a tendon and ligament; IM can coordinate muscular activity at heel strike and toe-off; IM limits separation of the distal tibio-fibular joint at heel strike; IM attenuates vertical ground reaction forces.

THE USEFULNESS OF SURFACE EMG RECORDINGS FOR EVALUATION OF THE SYNERGISTIC MUSCLE FUNCTIONS OF LOWER EXTREMITIES IN NORMAL CONDITIONS FOR PHYSIOTHERAPY

Introduction A sedentary lifestyle causes severe changes in the functioning of the trunk muscles, pelvic girdle and lower extremities in the population of healthy people. Understanding the synergies of muscles active while maintaining a standing position may, in this aspect, provide clinically helpful information for kinesiotherapy. There is little data on the assessment of synergistic muscles activity of the lower extremities using non-invasive polyelectromyography recorded with surface electrodes (sEMG) in a relaxed standing position, and due to the tendency of decreasing activation the proximal muscles, it can be expected that the previously developed movement patterns may have changed. Aim This pilot study aims to verify the activity of the lower extremities’ most crucial synergistic muscle groups engaged in posture maintenance in a population of healthy people using sEMG. Material and methods In a group of 14 healthy volunteers (7 women and 7 men), sEMG examination of the gluteus maximus (GM), rectus femoris (RF), tibialis anterior (TA), and dorsal foot extensors (EXT) was performed in 6 positions; resting in standing and lying, GM and RF maximal contraction in standing and lying and TA and EXT maximal contraction in standing and lying. A survey on daily activity was carried out among healthy volunteers. The output parameter of the sEMG tests was the mean value of the amplitude measured in microvolts. Results The subjects spent an average of 8 hours a day in a sitting position and 5.5 hours a day in a standing position. In the resting during standing position, the study of the electromyogram amplitude parameter showed a significant change in the involvement of the distal muscles of the lower extremity over proximal muscles (TA mean 67.5 µV; EXT mean 33.22 µV vs. GM mean 21.4 µV; RF mean 26.95 µV). The greatest tendency in changes of the lower extremities’ synergistic muscle function can be observed in the disproportion of proximal and distal muscle activity by about 60% in maintaining a relaxed standing position. Conclusions The gluteal muscles show dysfunctional changes resulting from the sedentary lifestyle; they are no longer synergistic with the rectus femoris muscles in relaxed standing. Pilot studies showed no significant disturbance of the synergy of proximal and distal muscles during the attempt of their maximal contraction in the supine position. A significant disproportion in activation of the synergistic distal muscles of the lower extremities in the standing position was demonstrated.

Architectural Changes in Superficial and Deep Compartments of the Tibialis Anterior During Electrical Stimulation Over Different Sites

Electrical stimulation is widely used in rehabilitation to prevent muscle weakness and to assist the functional recovery of neural deficits. Its application is however limited by the rapid development of muscle fatigue due to the non-physiological motor unit (MU) recruitment. This issue can be mitigated by interleaving muscle belly (mStim) and nerve stimulation (nStim) to distribute the temporal recruitment among different MU groups. To be effective, this approach requires the two stimulation modalities to activate minimally-overlapped groups of MUs. In this manuscript, we investigated spatial differences between mStim and nStim MU recruitment through the study of architectural changes of superficial and deep compartments of tibialis anterior (TA). We used ultrasound imaging to measure variations in muscle thickness, pennation angle, and fiber length during mStim, nStim, and voluntary (Vol) contractions at 15% and 25% of the maximal force. For both contraction levels, architectural changes induced by nStim in the deep and superficial compartments were similar to those observed during Vol. Instead, during mStim superficial fascicles underwent a greater change compared to those observed during nStim and Vol, both in absolute magnitude and in their relative differences between compartments. These observations suggest that nStim results in a distributed MU recruitment over the entire muscle volume, similarly to Vol, whereas mStim preferentially activates the superficial muscle layer. The diversity between spatial recruitment of nStim and mStim suggests the involvement of different MU populations, which justifies strategies based on interleaved nerve/muscle stimulation to reduce muscle fatigue during electrically-induced contractions of TA.

Ankle Dorsiflexion Strength Monitoring by Combining Sonomyography and Electromyography.

Ankle dorsiflexion produced by Tibialis Anterior (TA) muscle contraction plays a significant role during human walking and standing balance. The weakened function or dysfunction of the TA muscle often impedes activities of daily living (ADL). Powered ankle exoskeleton is a prevalent technique to treat this pathology, and its intelligent and effective behaviors depend on human intention detection. A TA muscle contraction strength monitor is proposed to evaluate the weakness of the ankle dorsiflexion. The new method combines surface electromyography (sEMG) signals and sonomyography signals to estimate ankle torque during a voluntary isometric ankle dorsiflexion. Changes in the pennation angle (PA) are derived from the sonomyography signals. The results demonstrate strong correlations among the sonomyography-derived PA, the sEMG signal, and the measured TA muscle contraction force. Especially, the TA muscle strength monitor approximates the TA muscle strength measurement via a weighted summation of the sEMG signal and the PA signal. The new method shows an improved linear correlation with the muscle strength, compared to the correlations between the muscle strength and sole sEMG signal or sole PA signal, where the R-squared values are improved by 4.21 % and 1.99 %, respectively.

The Use of Wearable Sensors for the Movement Assessment on Muscle Contraction Sequences in Post-Stroke Patients during Sit-to-Stand.

Electromyography (EMG) sensors have been used to study the sequence of muscle contractions during sit-to-stand (STS) in post-stroke patients. However, the majority of the studies used wired sensors with a limited number of placements. Using the latest improved wearable technology with 16 sensors, the current study was a thorough investigation to evaluate the contraction sequences of eight key muscles on the trunk and bilateral limbs during STS in post-stroke patients, as it became feasible. Multiple wearable sensors for the detection of muscle contraction sequences showed that the post-stroke patients performed STS with abnormal firing sequences, not only in the primary mover on the sagittal plane during raising, but also in the tibialis anterior, which may affect anticipatory postural adjustment in the gluteus medius, which may affect balance control. The abnormal tibialis anterior contraction until the early ascending phase and the delayed firing of the gluteus muscles highlight the importance of whole-kinetic-chain monitoring of contraction sequences using wearable sensors. The findings can be helpful for the design of therapeutic exercises.

Enlarged Areas of Pain and Pressure Hypersensitivityby Spatially Distributed Intramuscular Injections ofLow-Dose Nerve Growth Factor

Intramuscular injection of nerve growth factor (NGF) causes muscle hyperalgesia without immediate pain. This double-blinded, randomized study assessed pain and muscle hypersensitivity after a single-site bolus NGF injection (5 µg) compared with 5 spatially distributed, low-dose NGF injections (1 µg, 4 cm distance) into the tibialis anterior (TA) muscles in 20 healthy subjects. Injection pain was rated on a visual analog scale. Reports of muscle pain with functional tasks (Likert scale score) and the presence of spontaneous pain were collected daily by using a diary. Pressure pain threshold (PPT), overall pain intensity (numerical rating scale), and pain areas following the TA contraction were collected at baseline; 3 hours; and 1, 3, 7, 14, and 21 days postinjection. Low immediate visual analog scale scores were associated with both injection protocols. Likert scale scores showed moderate pain intensities but no spontaneous pain, until day 12, for both injection protocols (P < .05). Reduced PPTs at the 5- and 1-µg injection sites were found after 3 hours, lasting until day 7 (P < .05). The 1-µg injection provoked decreased PPTs at day 1 (P = .036) at the proximal injection site and at day 1 (P = .02) and day 3 (P = .01) at the distal injection site. The TA muscle contraction resulted in larger pain areas and higher numerical rating scale scores at day 3 for the distributed injections compared with the single-site injection (P < .001).Perspective: Spatially distributed low-dose NGF injections induced prolonged pain, mechanical muscle hypersensitivity, and enlarged contraction-evoked pain areas. These features mirror some clinical muscle pain conditions in which diffuse pain areas and muscle hypersensitivity are present during the activities of daily living. Low-dose NGF injections may be useful for further studies of prolonged pain conditions.

Stumbling corrective reaction elicited by mechanical and electrical stimulation of the saphenous nerve in walking mice.

The ability to walk around in a natural environment requires the capacity to cope with unexpected obstacles that may disrupt locomotion. One such mechanism is called the stumbling corrective reaction (SCR) that enables animals to step over obstacles that would otherwise disturb the progression of swing movement. Here we use in vivo motion analysis and physiological recording techniques to describe the SCR in mice. We show that SCR can be elicited consistently in mice during locomotion by inserting an obstacle along the path of leg movement during swing phase. Furthermore, we show that the same behavior can be elicited if the saphenous nerve, a cutaneous nerve that would detect contact of the leg with an object, is stimulated electrically. This suggests that cutaneous afferent feedback is sufficient to elicit SCR. We further show that the SCR is phase dependent, occurring only with stimulation during swing phase, but not during early stance. During SCR elicited by either method, the foot is lifted higher to clear the object by flexing the knee, via the semitendinosus muscle, and ankle joint, by tibialis anterior contraction. The tibialis anterior also exhibits a brief extension before flexion onset. Our data provide a detailed description of SCR in mice and will be crucial for future research that aims to identify the interneurons of the premotor network controlling SCR and its neuronal mechanisms by combining motion analysis, electrophysiology and mouse genetics.

Модулирующее влияние адреналина на развитие стероидной миопатии у белых крыс, индуцированной длительным введением гидрокортизона

Цель исследования - изучение эффективности адреналина в компенсации негативных эффектов длительно вводимого гидрокортизона на скелетную мышцу смешанного типа. Методика. Эксперименты проводились на половозрелых крысах-самках (190-220 г), разделенных на 3 группы: контрольную (n = 10), I опытную (n = 10, ежедневно на протяжении 30 сут. получали гидрокортизона ацетат, Г-группа) и II опытную (n = 10, ежедневно на протяжении 30 сут. получали гидрокортизона ацетат в комплексе с адреналина гидрохлоридом, (Г+А)-группа). Гидрокортизона ацетат («Фармак», Украина) вводили внутрибрюшинно в дозе, адекватной терапевтической для человека, - 3 мг/кг. Адреналина гидрохлорид («Здоровье», Украина) вводили подкожно в дозе 0,2 мг/кг. На наркотизированных животных (тиопентал натрия, 100 мг/кг) с помощью методов электромиографии и миографии изучали параметры функционального состояния передней большеберцовой мышцы в условиях ее сокращения, индуцированного раздражением сверхпороговым электрическим током малоберцового нерва. Результаты. Длительное (в течение 30 сут.) введение гидрокортизона вызывало развитие симптомов стероидной миопатии, о чем свидетельствует появление низкоамплитудных М-ответов нормальной длительности, возрастание частоты полифазных потенциалов (до 30%), уменьшение количества активируемых двигательных единиц (на 33%) и мышечной массы (на 14%). Гидрокортизоновый гиперкортицизм сопровождался удлинением латентного периода одиночного сокращения передней большеберцовой мышцы (на 37%) и фазы его укорочения (на 20%), уменьшением амплитуды одиночных сокращений (на 32%), объема выполненной мышцей внешней работы (на 40%) и развиваемой мощности (на 41%) при тетаническом сокращении. Отмечены нарушения в целостном процессе нервно-мышечной передачи, что проявлялось в уменьшении степени ее надежности (у 30% особей), выраженном облегчении (более 85% у 50% особей) или депрессии (до -42% у 40% особей) при стимуляции нервно-мышечного аппарата с оптимальной частотой (30 имп/с). Адреналин, вводимый в комплексе с гидрокортизоном, предотвращал появление ряда симптомов миопатии, таких, как снижение амплитуды М-ответов, уменьшение количества активируемых двигательных единиц мышцы, ее массы, внешней работы и мощности, а также обусловливал уменьшение частоты генерации полифазных М-ответов (с 30% до 10%). Кроме того, адреналин ослаблял негативный эффект гидрокортизона на синаптический аппарат, что проявлялось в уменьшении частоты встречаемости сниженной надежности синаптической передачи (с 30% до 10%), выраженного ее облегчения (с 50% до 20%) и депрессии (с 40% до 10%) у животных (Г+А)-группы в сравнении с Г-группой. Заключение. Полученные в модельных экспериментах на животных в условиях in situ данные свидетельствуют о способности адреналина эффективно компенсировать ряд негативных эффектов, развивающихся в скелетной мышце при длительном введении гидрокортизона. Based on the beneficial effect of chronic adrenergic stimulation on the neuromuscular apparatus function, the aim of this study was to evaluate efficacy of adrenaline at therapeutic doses in compensation for adverse effects of chronically administered hydrocortisone on mixed-fiber type skeletal muscles ( m. tibialis anterior ). Method. Experiments were performed on sexually mature female rats (190-220 g) divided into 3 groups: control (n = 10), experimental group 1 (H group, n = 10, hydrocortisone acetate, for 30 days daily), and experimental group 2 (H+A group, n = 10, hydrocortisone acetate in combination with adrenaline hydrochloride, for 30 days daily). Hydrocortisone acetate (Farmak, Ukraine) was injected i.p. at a dose of 0.2 mg/kg, which was equivalent to the human therapeutic dose of 3 mg/kg. Adrenaline hydrochloride (Zdorovje, Ukraine) was injected s.c. at a dose of 0.2 mg/kg. Parameters of the tibialis anterior muscle function were studied on anesthetized animals (sodium thiopental, 100 mg/kg) using electromyography and myography methods. Muscle contractions were induced by suprathreshold electrical stimulation of the fibular nerve. Results. Chronic administration (30 days) of hydrocortisone caused symptoms of steroid myopathy evident as low-amplitude M-waves of normal duration, increased frequency of polyphase potentials (by 30%), decreased quantity of activated motor units (by 33%), and decreased muscle mass (by 14%). Hydrocortisone-induced hypercorticoidism was associated with prolonged latent period (by 37%) and shortening phase (by 20%) and decreased amplitude (by 32%), amount of muscular external work (by 40%) in a single tibialis anterior muscle contraction, and decreased muscular power (by 41%) developed in a tetanic contraction. Following repeated hydrocortisone injections, the overall process of neuromuscular transmission was disturbed, which was evident as its impaired reliability (30% of rats) and pronounced facilitation (&gt;85% in 50% of rats) or depression (&lt;-42% in 40% of rats) at an optimum stimulation frequency (30 imp/s). Adrenaline administered in combination with hydrocortisone prevented formation of myopathy symptoms, such as decreases in the M-wave amplitude, number of activated motor units, muscle weight, external work and power, and it also decreased the frequency of polyphase M-waves (from 30% to 10%). In addition, adrenaline attenuated the adverse effect of hydrocortisone on the synaptic apparatus by decreasing the incidence of reduced reliability of synaptic transmission (from 30% to 10%), facilitation (from 50% to 20%), and depression (from 40% to 10%) in the H+A-group compared to the H group. Conclusion. The experimental data obtained in model experiments on animals in situ support the adrenaline ability to effectively compensate for a number of adverse effects of chronic hydrocortisone treatment on the skeletal muscle.

Applying surface electromyography in limb function rehabilitation after stroke

Objective To evaluate the effect of surface electromyography (sEMG) applied bilaterally to the limbs in the rehabilitation of motor dysfunction among stroke survivors. Methods Sixty stroke survivors were randomized into a bilateral group (n=30) and a control group (n=30). Both groups received routine rehabilitation for 4 weeks, but the bilateral group accepted additional limb rehabilitation training for the uninjured side. Before and after the intervention, motor function was assessed using sEMG during maximal voluntary contraction of the deltoid, biceps, triceps, rectus femoris, biceps femoris and tibialis anterior muscles. Integrated EMG (iEMG) and root mean square (RMS) values were computed. Results Before the training there was no significant difference in any of the measurements between the two groups. After the training both groups had significantly improved the average strength of their maximum contractions and their average iEMG and RMS values. The bilateral group, though, demonstrated significantly better results than the control group. Conclusion Bilateral limb rehabilitation training is superior to the conventional unilateral procedure in improving the motor function of stroke survivors. Key words: Stroke; Limb function; Motor function; Surface electromyography

Effect of constitutive inactivation of the myostatin gene on the gain in muscle strength during postnatal growth in two murine models.

The effect of constitutive inactivation of the gene encoding myostatin on the gain in muscle performance during postnatal growth has not been well characterized. We analyzed 2 murine myostatin knockout (KO) models, (i) the Lee model (KOLee ) and (ii) the Grobet model (KOGrobet ), and measured the contraction of tibialis anterior muscle in situ. Absolute maximal isometric force was increased in 6-month-old KOLee and KOGrobet mice, as compared to wild-type mice. Similarly, absolute maximal power was increased in 6-month-old KOLee mice. In contrast, specific maximal force (relative maximal force per unit of muscle mass was decreased in all 6-month-old male and female KO mice, except in 6-month-old female KOGrobet mice, whereas specific maximal power was reduced only in male KOLee mice. Genetic inactivation of myostatin increases maximal force and power, but in return it reduces muscle quality, particularly in male mice. Muscle Nerve 55: 254-261, 2017.

Accurate and representative decoding of the neural drive to muscles in humans with multi-channel intramuscular thin-film electrodes.

Intramuscular electrodes developed over the past 80 years can record the concurrent activity of only a few motor units active during a muscle contraction. We designed, produced and tested a novel multi-channel intramuscular wire electrode that allows in vivo concurrent recordings of a substantially greater number of motor units than with conventional methods. The electrode has been extensively tested in deep and superficial human muscles. The performed tests indicate the applicability of the proposed technology in a variety of conditions. The electrode represents an important novel technology that opens new avenues in the study of the neural control of muscles in humans. We describe the design, fabrication and testing of a novel multi-channel thin-film electrode for detection of the output of motoneurones in vivo and in humans, through muscle signals. The structure includes a linear array of 16 detection sites that can sample intramuscular electromyographic activity from the entire muscle cross-section. The structure was tested in two superficial muscles (the abductor digiti minimi (ADM) and the tibialis anterior (TA)) and a deep muscle (the genioglossus (GG)) during contractions at various forces. Moreover, surface electromyogram (EMG) signals were concurrently detected from the TA muscle with a grid of 64 electrodes. Surface and intramuscular signals were decomposed into the constituent motor unit (MU) action potential trains. With the intramuscular electrode, up to 31 MUs were identified from the ADM muscle during an isometric contraction at 15% of the maximal force (MVC) and 50 MUs were identified for a 30% MVC contraction of TA. The new electrode detects different sources from a surface EMG system, as only one MU spike train was found to be common in the decomposition of the intramuscular and surface signals acquired from the TA. The system also allowed access to the GG muscle, which cannot be analysed with surface EMG, with successful identification of MU activity. With respect to classic detection systems, the presented thin-film structure enables recording from large populations of active MUs of deep and superficial muscles and thus can provide a faithful representation of the neural drive sent to a muscle.

Facilitating myoelectric-control with transcranial direct current stimulation: a preliminary study in healthy humans

BackgroundFunctional Electrical Stimulation (FES) can electrically activate paretic muscles to assist movement for post-stroke neurorehabilitation. Here, sensory-motor integration may be facilitated by triggering FES with residual electromyographic (EMG) activity. However, muscle activity following stroke often suffers from delays in initiation and termination which may be alleviated with an adjuvant treatment at the central nervous system (CNS) level with transcranial direct current stimulation (tDCS) thereby facilitating re-learning and retaining of normative muscle activation patterns.MethodsThis study on 12 healthy volunteers was conducted to investigate the effects of anodal tDCS of the primary motor cortex (M1) and cerebellum on latencies during isometric contraction of tibialis anterior (TA) muscle for myoelectric visual pursuit with quick initiation/termination of muscle activation i.e. 'ballistic EMG control’ as well as modulation of EMG for 'proportional EMG control’.ResultsThe normalized delay in initiation and termination of muscle activity during post-intervention 'ballistic EMG control’ trials showed a significant main effect of the anodal tDCS target: cerebellar, M1, sham (F(2) = 2.33, p < 0.1), and interaction effect between tDCS target and step-response type: initiation/termination of muscle activation (F(2) = 62.75, p < 0.001), but no significant effect for the step-response type (F(1) = 0.03, p = 0.87). The post-intervention population marginal means during 'ballistic EMG control’ showed two important findings at 95% confidence interval (critical values from Scheffe’s S procedure): 1. Offline cerebellar anodal tDCS increased the delay in initiation of TA contraction while M1 anodal tDCS decreased the same when compared to sham tDCS, 2. Offline M1 anodal tDCS increased the delay in termination of TA contraction when compared to cerebellar anodal tDCS or sham tDCS. Moreover, online cerebellar anodal tDCS decreased the learning rate during 'proportional EMG control’ when compared to M1 anodal and sham tDCS.ConclusionsThe preliminary results from healthy subjects showed specific, and at least partially antagonistic effects, of M1 and cerebellar anodal tDCS on motor performance during myoelectric control. These results are encouraging, but further studies are necessary to better define how tDCS over particular regions of the cerebellum may facilitate learning of myoelectric control for brain machine interfaces.

Foot Drop Caused by a Lesion in the Thoracolumbar Spine

Fifteen patients with foot drop caused by a thoracolumbar spine lesion were retrospectively investigated. To clarify surgical outcomes and prognostic factors for foot drop owing to thoracolumbar disease. Although the literature contains some reports of the surgical outcome for foot drop because of lumbar degenerative disease, to the best of our knowledge, little is known about foot drop resulting from thoracolumbar lesions. Thoracolumbar lesions were classified into 2 groups (ossification of the ligamentum flavum; OLF, and osteoporotic vertebral collapse; OVC). Mean age at surgery was 73.7 years (range, 62 to 84 y) and the average follow-up period was 50 months (range, 19 to 85 mo). We measured the muscle strength of the tibialis anterior (TA) before operation and at the last follow-up. Diagnosis (OLF or OVC), age, sex, preoperative TA strength, and palsy duration were compared according to surgical outcome. Excellent or good surgical outcomes were seen in 87% of patients with foot drop. Of the 8 patients who were chairbound or bedridden preoperatively, 5 (62.5%) were able to walk with the aid of a cane at the last follow-up. OVC patients, those with palsy duration shorter than 3 months, and those with good TA muscle contraction in response to peroneal nerve stimulation had a better surgical outcome. Prognosis of foot drop was much better when the causative lesion was at the thoracolumbar spine than when it was at the lumbar spine. Severe paralysis was not a poor prognostic factor.

Repetitive common peroneal nerve stimulation increases ankle dorsiflexor motor evoked potentials in incomplete spinal cord lesions

Plasticity of corticospinal tract (CST) activity likely plays a key role in motor function recovery after central nervous system (CNS) lesions. In non-injured adults, 30min of repetitive common peroneal nerve stimulation (rCPnS) increases CST excitability by 40-50% and the effect persists for at least 30min. The present study evaluated with transcranial magnetic stimulation (TMS) the changes in CST excitability after 30min of rCPnS in people with foot drop due to incomplete SCI. Suprathreshold rCPnS (25Hz, alternating 1s on 1s off stimulation cycle) was given for two 15-min periods, while the subject sat at rest with ankle and knee joints fixed. Before, between, and after the periods of stimulation, the tibialis anterior (TA) motor evoked potentials (MEPs) to TMS were measured at a TMS intensity that originally produced a half-maximum MEP (typically 10-20% above threshold) while the sitting subject provided 25-30% maximum voluntary TA contraction. In 10 subjects with SCI, the peak-to-peak TA MEP increased by 14±3% after rCPnS and the peak increase (+21±7%) occurred 15min after the cessation of rCPnS. The TA H-reflex, measured in separate experiments in 7 subjects, did not increase after rCPnS. The results indicate that rCPnS can increase CST excitability for the TA in people with incomplete SCI, although its effects appear smaller and shorter lasting than those found in non-injured control subjects. Such short-term plasticity in the CST excitability induced by rCPnS may contribute to long-term therapeutic effects of functional electrical stimulation previously reported in people with CNS lesions.

Role of the premotor cortex in leg selection and anticipatory postural adjustments associated with a rapid stepping task in patients with stroke

The premotor cortex (PMC) plays an important role in selecting and preparing for movement. This study investigates how stroke-induced PMC lesions affect stepping leg selection and anticipatory postural adjustments (APAs) preparation. Fifteen hemi-paretic patients (eight with PMC lesions (PMC Lesion) and seven PMC spared (PMC Spared)) and eight age- and sex-matched healthy adults participated in the study. The subjects performed rapid forward stepping with the right or left leg under simple and choice reaction time conditions. The percentage of trials in which the subject showed the correct initial vertical ground reaction force pattern before lift-off of the stepping leg indicated the accuracy in selecting the designated stepping leg. The latency of bilateral contractions in the tibialis anterior (TA) and the reaction time (RT) of the stepping leg represented the time needed to prepare for stepping-related APAs and stepping movement, respectively. All three groups demonstrated a similar rate of accuracy of the stepping leg selection under both conditions. However, in both conditions, the PMC Lesion group exhibited a longer RT and TA contraction latency of the affected leg than the healthy and PMC Spared groups. The PMC Lesion group also presented a longer TA contraction latency of the unaffected leg than the healthy group in both conditions. These results suggest that the PMC is involved in APAs associated with leg stepping movement and that a PMC lesion in one hemisphere impairs APAs of both the contralateral and ipsilateral legs during stepping.

Investigation of motor unit recruitment during stimulated contractions of tibialis anterior muscle

This work investigated motor unit (MU) recruitment during transcutaneous electrical stimulation (TES) of the tibialis anterior (TA) muscle, using experimental and simulated data. Surface electromyogram (EMG) and torque were measured during electrically-elicited contractions at different current intensities, on eight healthy subjects. EMG detected during stimulation (M-wave) was simulated selecting the elicited MUs on the basis of: (a) the simulated current density distribution in the territory of each MU and (b) the excitation threshold characteristic of the MU. Exerted force was simulated by adding the contribution of each of the elicited MUs. The effects of different fat layer thickness (between 2 and 8 mm), different distributions of excitation thresholds (random excitation threshold, higher threshold for larger MUs or smaller MUs), and different MU distributions within the muscle (random distribution, larger MU deeper in the muscle, smaller MU deeper) on EMG variables and torque were tested. Increase of the current intensity led to a first rapid increase of experimental M-wave amplitude, followed by a plateau. Further increases of the stimulation current determined an increase of the exerted force, without relevant changes of the M-wave. Similar results were obtained in simulations. Rate of change of conduction velocity (CV) and leading coefficient of the second order polynomial interpolating the force vs. stimulation level curve were estimated as a function of increasing current amplitudes. Experimental data showed an increase of estimated CV with increasing levels of the stimulation current (for all subjects) and a positive leading coefficient of force vs. stimulation current curve (for five of eight subjects). Simulations matched the experimental results only when larger MUs were preferably located deeper in the TA muscle (in line with a histochemical study). Marginal effect of MU excitation thresholds was observed, suggesting that MUs closer to the stimulation electrode are recruited first during TES regardless of their excitability.

Delay in Initiation and Termination of Tibialis Anterior Contraction in Lower-Limb Hemiparesis: Relationship to Lower-Limb Motor Impairment and Mobility

Chae J, Quinn A, El-Hayek K, Santing J, Berezovski R, Harley M. Delay in initiation and termination of tibialis anterior contraction in lower-limb hemiparesis: relationship to lower-limb motor impairment and mobility. Objective To assess the relationship between delays in initiation and termination of tibialis anterior contraction in the hemiplegic lower limb and clinical measures of lower-limb motor impairment and mobility. Design Cross-sectional correlational study. Setting Outpatient rehabilitation clinic of an academic medical center. Participants Convenience sample of 22 chronic stroke survivors with lower-limb hemiparesis. Interventions Not applicable. Main Outcome Measures Delays in initiation and termination of tibialis anterior electromyographic activity during isometric contraction, lower-limb Fugl-Meyer Assessment (FMA), and Modified Emory Functional Ambulation Profile (mEFAP). Results The affected lower limb exhibited significantly longer delays in initiation and termination of tibialis anterior contraction relative to the unaffected limb. Delay in termination of 3-second tibialis anterior contraction of the affected limb correlated significantly with the FMA and mEFAP. However, delay in initiation of tibialis anterior contraction did not correlate with clinical measures. Conclusions Delay in termination of muscle activity in the hemiparetic lower limb may have important clinical implications, but delay in initiation did not correlate with clinical measures. Controlled, interventional trials are needed to demonstrate a cause and effect relationship.

Short- and Long-Latency Contributions to Reciprocal Inhibition During Various Levels of Muscle Contraction of Individuals With Cerebral Palsy

Deficits in reciprocal inhibition likely contribute to excessive antagonist muscle cocontraction during voluntary movements of individuals with cerebral palsy. This study examined neural contributions to reciprocal inhibition of the soleus motoneurons of individuals with spastic, diplegic cerebral palsy and nondisabled individuals during various levels of voluntary tibialis anterior contraction. A condition-test H-reflex paradigm examined short- and long-latency contributions to reciprocal inhibition of soleus neural pools during changing levels of voluntary tibialis anterior contraction. Electrically induced short- and long-latency inhibition was similar between healthy, neurologically intact control subjects and subjects with cerebral palsy during rest. With increasing levels of tibialis anterior contraction, control subjects experienced increasing levels of soleus motoneuron inhibition, especially of long-latency inhibitory responses. In contrast, there was no evidence of modulation of short- or long-latency inhibition with increasing levels of tibialis anterior contraction among subjects with cerebral palsy. Deficits in long-latency (presynaptic) inhibition appear to contribute prominently to voluntary movement impairment of individuals with cerebral palsy.

NATURAL RECIPROCAL INHIBITION OF SOLEUS H-REFLEX DURING EARLY PHASE OF GAIT INITATION; DIFFERENCE BETWEEN SWING AND STANCE LIMB.

PURPOSE/HYPOTHESIS: This experiment was done to investigate soleus (SOL) H-reflex for swing limb and stance limb during the pre-motor reaction time (RT) period, which was determined by onset of tibialis anterior (TA) and during the early phase of gait initiation (GI) relative to the kinetic and kinematic events in the process of GI compaired to standing. NUMBER OF SUBJECTS: Six male and seven female subjects without known medical, orthopedic and/or neurological condition were recruited in this study. Average age was 29.86 6.6 years. MATERIALS/METHODS: SOL and TA electromyogram (EMG) and SOL H-reflexes were recorded from the right limb of subjects during GI. Ground reaction force under the testing foot was also monitored. Subjects were tested in three different paradigms; standing, stance GI, and swing GI paradigms. To obtain H-reflexes for various time periods of GI, the stimulus was delivered at various times relative to the onset of light switch signal. The delay for administration of the stimulus following the onset of the light signal was vary. The beginning of GI was determined by the onset of TA EMG activity. RESULTS: Both stance and swing limb H-reflexes were significantly and gradually depressed during reaction time (RT) of GI. However, the H-reflexes in the initial RT periods were significantly lower and their depression started earlier on the impending stance limb (150 to 125ms prior to TA EMG onset; to 11.9% of standing value) than the swing limb (50 ms before the TA EMG onset; 37.9% of standing value). The H-reflexes for both stance and swing limbs after the TA EMG onset were closely modulated with changes in ground reaction forces rather than the amount of TA EMG activity. Although there was some inhibition of the H-reflex due to TA contraction during the initial G1, the effect was relatively weak, particularly when the leg was the loading limb which was responsible for the forward acceleration force. CONCLUSIONS: Such findings indicate that the SOL H-reflex inhibition was relatively weak when the leg was the loading limb, which was responsible for the major acceleration force and provides evidence that the H-reflex is centrally modulated and depends on the role of the muscle during a given task. The loading limb may need to maintain a higher gain for SOL activity to adjust to the changes in peripheral events. We speculate that GI is a preprogrammed task and the H-reflex modulation during RT and the early phase of GI is primarily under central control with possibly some contribution from peripheral afferents. CLINICAL RELEVANCE: The result of this work are related to the rehabilitation of those with central nervous system (CNS) disorders who have difficulty with precise and timely modulation of SOL excitability between the stance and the swing legs during GI. Future clinical research including both legs of people with CNS disorders would help rehabilitation clinicians enhance their knowledge of the nature of difficulties in GI, the development of effective training protocols or facilitating GI.

Electromechanical delay estimated by using electromyography during cycling at different pedaling frequencies

The purpose of this study was to propose a new method that can be used to calculate electromechanical delay (EMD) without the measurement of forces. A secondary purpose, as an example of the importance of measuring EMD, was to predict muscle force development events based on the EMG activity of selected muscles during cycling at different pedaling frequencies. EMD was estimated using newly derived equations based on activation dynamics hypothesis. Tibialis anterior (TA) and soleus (SL) muscles of 16 male participants were studied while subjects pedaled at targeted cadences of 60, 80, and 100 revolutions per minute. The estimated EMDs of TA and SL were significantly different from each other with means of 68.1 and 88.7 ms, respectively. The average crank angle for the initiation and time to peak TA contraction was estimated at 75±35° and 26±15° before the crank reached top-dead-center (TDC), while the contraction ended at 31±19° after the TDC on average. The projected starting, peak and end angles of SL contraction activity were 45±18°, 123±13°, and 218±35° after the TDC, respectively. There was no difference among different pedaling cadences observed for these mechanical events. The proposed method was proven to be effective in studying EMD and estimate muscle contraction patterns during cycling.