Leg Muscle Activity Research Articles

Analysis of Connectivity in Electromyography Signals to Examine Neural Correlations in the Activation of Lower Leg Muscles for Postural Stability: A Pilot Study.

In quiet standing, the central nervous system implements a pre-programmed ankle strategy of postural control to maintain upright balance and stability. This strategy comprises a synchronized common neural drive delivered to synergistically grouped muscles. This study evaluated connectivity between EMG signals of the unilateral and bilateral homologous muscle pairs of the lower legs during various standing balance conditions using magnitude-squared coherence (MSC). The leg muscles examined included the right and left tibialis anterior (TA), medial gastrocnemius (MG), and soleus (S). MSC is a frequency domain measure that quantifies the linear phase relation between two signals and was analyzed in the alpha (8-13 Hz), beta (13-30 Hz), and gamma (30-100 Hz) neural frequency bands for feet together and feet tandem, with eyes open and eyes closed conditions. Results showed that connectivity in the beta and lower and upper gamma bands (30-100 Hz) was influenced by standing balance conditions and was indicative of a neural drive originating from the motor cortex. Instability was evaluated by comparing less stable standing conditions with a baseline-eyes open feet together stance. Changes in connectivity in the beta and gamma bands were found to be most significant in the muscle pairs of the back leg during a tandem stance regardless of dominant foot placement. MSC identified the MG:S muscle pair as significant for the right and left leg. The results of this study provided insight into the neural mechanism of postural control.

The Effect of Foot Position on Lower Leg Muscle Activity in Flatfoot: during Pilates Reformer Footwork Exercise

The Effect of Foot Position on Lower Leg Muscle Activity in Flatfoot: during Pilates Reformer Footwork Exercise

The Effect of Dominant Side Leg Exercise in Different Environments with and without Resistance on Non-Dominant Leg Muscle Activation: Sitting Position

The Effect of Dominant Side Leg Exercise in Different Environments with and without Resistance on Non-Dominant Leg Muscle Activation: Sitting Position

Acute Neuromuscular Fatigue of a Random Vs Constant Session of Repeated Standing Long Jumps.

There is little evidence of the acute effect of random practice, performed by solely varying the intensity but not the task itself, as compared to block practice, i.e. when one task is repeated in a constant manner. This study aimed to examine the acute neuromuscular effects of physical exercise consisting of repeated jumps of randomized length. Fifteen healthy young participants completed 2 separate sessions of 90 minutes. They did 20 minutes of fatiguing exercise, consisting of 100 repeated standing long jumps (SLJ), in two different manners: one session with targeted jump length kept constant (CO), and one with targeted jump length being varied and unpredictable (RA). Pre- and post-tests were conducted before and immediately after, including measurements of Countermovement Jump (CMJ), SLJ, leg extension maximal voluntary isometric contractions (MViC), EMG activities of leg muscles and patellar tendon reflex amplitude (T-reflex: strike force and evoked force). Results showed that performances decreased after the repeated SLJs, independently of the condition (MViC decreased from 448 ± 118 N to 399 ± 122 N; CMJ decreased from 36.7 ± 7.2 cm to 34.6 ± 6.6 cm). EMG during MViC decreased by 21 ± 28 % from pre- to post-intervention. T-reflex decreased after both conditions ([Force/Strike] ratio decreased by 38 ± 69 % from pre to post). Subjective measures showed a greater sense of personal performance and enjoyment after the RA session. Results suggest that a randomly organized intensity of effort led to a similar decrease in physical performance compared to constant intensity when the session loads were matched. It also led to similar fatigue of the neuromuscular system as shown by T-reflexes and EMG measures. Nonetheless, random practice presents the benefit of being markedly more appreciated by participants.

Effects of Fatigue on Ankle Flexor Activity and Ground Reaction Forces in Elite Table Tennis Players.

Fatigue specifically affects the force production capacity of the working muscle, leading to a decline in athletes' performance. This study investigated the impact of fatigue on ankle flexor muscle activity and ground reaction forces (GRFs) in elite table tennis players, with a focus on the implications for performance and injury risk. Twelve elite male table tennis athletes participated in this study, undergoing a fatigue protocol that simulated intense gameplay conditions. Muscle activity of the soleus (SOL) and gastrocnemius lateralis (GL) muscles, heel height, and GRFs were measured using a combination of wireless electromyography (EMG), motion capture, and force plate systems. Results showed a significant decrease in muscle activity in both legs post-fatigue, with a more pronounced decline in the right leg. This decrease in muscle activity negatively affected ankle joint flexibility, limiting heel lift-off. Interestingly, the maximal anteroposterior GRF generated by the left leg increased in the post-fatigue phase, suggesting the use of compensatory strategies to maintain balance and performance. These findings underscore the importance of managing fatigue, addressing muscle imbalances, and improving ankle flexibility and strength to optimize performance and reduce the risk of injuries.

The human lower leg muscle pump functions as a flow diverter pump, maintaining low ambulatory venous pressures during locomotion

ObjectiveAmbulatory venous pressure (AVP) is the drop of pressure observed in the superficial veins of the lower leg during movement. This phenomenon has been linked to the function of the calf muscle pump (CMP) and the competence of venous valves. Nevertheless, the concept of the CMP function remains controversial. This study aimed to elucidate the association between lower leg muscles activity, changes in pressure in distinct venous segments, and lower extremity arterial blood supply in healthy subjects during various types and intensities of exercise. MethodsTwelve legs of nine healthy volunteers were enrolled in the study. Continuous pressure (intramuscular vein [IV] and three great saphenous vein [GSV] points) and surface electromyography data (gastrocnemius and anterior tibial [ATM] muscles) were recorded during treadmill walking, running, and plantar flexion exercises. The pressure gradient (ΔP, mmHg) between adjacent points of measurement was calculated. Minute unit power of muscle pump ejection and suction (NE, and NS, MPa/min) were calculated and compared with the arterial blood supply of the lower extremity (LBF, L/min). ResultsΔP demonstrated a consistent pattern of changes during walking and running. In GSV, the ΔP was observed to be directed from the thigh to the mid-calf (retrogradely) and from the ankle to the mid-calf (anterogradely) throughout the entire stride cycle. However, its value decreased with increasing stride cycle frequency. The dynamics of ΔP between the IV and GSV were as follows: It was directed from the IV to GSV during gastrocnemius contraction and was reversed during anterior tibial muscle contraction and gastrocnemius relaxation (swing phase). LBF, NE, and NS demonstrated similar exponential growth with increasing stride frequency during walking and running. ConclusionsDuring natural locomotion, the muscle pump acts as a flow diverter pump, redirecting the flow of blood from the superficial veins to the intramuscular veins via the perforating veins. During ambulation, the pressure in the superficial venous network depends upon the capacity of the muscle pump to provide output that matches the changes in arterial blood flow.

Prevalence of autonomic dysreflexia during spinal cord stimulation after spinal cord injury.

Over the past decade, clinical trials have shown that spinal cord stimulation can restore motor functions that were thought to be permanently impaired in persons with spinal cord injury. However, the off-target effects of delivering electrical impulses to intertwined spinal networks remain largely unknown. This generates safety concerns for this otherwise fast-progressing technology. Herein, we present the prevalence of autonomic dysreflexia (AD) that occurred during implanted spinal cord stimulation testing for motor activation of the lower extremities. Eleven participants with spinal cord injury underwent implantation of temporary percutaneous epidural and dorsal root ganglia stimulation leads. Participants completed two days of parameter testing at baseline, then six days of motor rehabilitation sessions, and two days of parameter testing at end of study. The goal of parameter testing was to determine electrode configuration(s), pulse amplitudes, and frequencies that activated lumbosacral spinal sensorimotor networks that generate lower extremity functions. During all parameter testing sessions, continuous blood pressure and heart rate monitoring recordings were collected. Evidence of autonomic dysreflexia was found in 22% of all parameter tests with participants at rest. Most of these episodes (97%) were asymptomatic. These episodes occurred more frequently when using epidural stimulation, at or near amplitudes that elicited whole leg muscle activation and using a wide-field electrode configuration. Although monitoring occurred during passive testing, motor rehabilitation sessions use stimulation for longer periods, at higher frequencies and amplitudes. These sessions may carry additional risks of autonomic dysreflexia. Investigation of these concerns should continue as spinal cord stimulation progresses toward clinical translation.NEW & NOTEWORTHY Spinal cord stimulation for motor recovery after spinal cord injury is a popular research intervention, though off-target effects are a concern. Using continual blood pressure and heart rate recordings during passive spinal cord stimulation parameter testing, we identified frequent episodes of autonomic dysreflexia that were rarely associated with symptoms. This presents a previously unrecognized risk of spinal cord stimulation and appropriate vigilance in targeted monitoring is urged to maintain participant safety.

Acute Effects of Soft Tissue Modalities on Muscular Ultrasound Characteristics and Isometric Performance

Prior to training, many athletes perform different soft-tissue preparation protocols. Many of these protocols involve stretching, foam rolling, and/or percussion massage. Many of these modalities have been studied, but not as a group to observe muscle alterations and differences in males and females. In total, 40 (20 males, 20 females) participants performed five minutes of static stretching, foam rolling, and percussion massage. Pre- and post-isometric leg strength, muscle activation and ultrasound assessments (cross-sectional area, echo intensity, pennation angle, fascicle length, and muscle thickness) were taken. The results indicate that there is no significant difference among modalities, and that they do not significantly alter any muscle characteristic or improve performance. There is a significant difference in size between males and female, with males having larger muscle and greater pennation angles than females. This allows males to generate significantly more muscle force. However, they both respond similarly to each modality. In conclusion, the muscle response to static stretching, foam rolling, and percussion massage do not differ among modalities and do not contribute to an increase or decrease in maximal isometric knee extension with similar effects between males and females.

Ballet practice improves neuromuscular and biomechanical responses to an unexpected standing-slip in older adults.

Falls and fall-induced injuries are common and consequential in older adults. Ballet emphasizes full-body coordination, leg strength, and postural control. However, it remains unknown whether ballet can indeed reduce falls in older adults. This study examined biomechanical and neuromuscular responses of older recreational ballet dancers to an unexpected standing-slip. Twenty older ballet dancers (17 females, 3 males) and 23 age- and sex-matched nondancers (19 females, 4 males) were exposed to an unexpected slip during treadmill standing. The slip-faller rate was the primary outcome. The secondary outcomes were kinematic measurements, including dynamic gait stability, slip distance, and recovery stepping performance (step latency, duration, length, and speed). The tertiary outcome was the electromyography latency of leg muscles (bilateral tibialis anterior, medial gastrocnemius, rectus femoris, and biceps femoris). Fewer dancers fell than nondancers after the standing-slip (45% vs. 83%, P = 0.005, d = 0.970). Dancers displayed better stability at recovery foot liftoff (P = 0.006) and touchdown (P = 0.012), a shorter step latency (P = 0.020), shorter step duration (P = 0.011), faster step speed (P = 0.032), and shorter slip distance (P = 0.015) than nondancers. They also exhibited shorter latencies than nondancers for the standing leg rectus femoris (P = 0.028) and tibialis anterior (P = 0.002), and the stepping leg biceps femoris (P = 0.031), tibialis anterior (P = 0.017), and medial gastrocnemius (P = 0.030). The results suggest that older ballet dancers experience a lower fall risk and are more stable than nondancers following an unexpected standing-slip. The greater stability among dancers could be attributed to more biomechanically effective recovery stepping, possibly associated with the ballet-induced neuromuscular benefit-an earlier leg muscle activation.NEW & NOTEWORTHY This is the first study to examine how older ballet dancers respond to an unexpected external slip perturbation while standing. The results suggest that older ballet dancers experience a reduced fall risk after the slip than their nondancer counterparts. The lower fall risk can be accounted for by dancers' quicker neuromuscular reactions to the slip that result in a more effective recovery step and thus higher stability against backward falls due to the slip.

Acute cardiovascular and muscular response to rowing ergometer exercise in artificial gravity – a pilot trial

Prolonged immobilization and spaceflight cause cardiovascular and musculoskeletal deconditioning. Combining artificial gravity through short-arm centrifugation with rowing exercise may serve as a countermeasure. We aimed to compare the tolerability, muscle force production, cardiovascular response, and power output of rowing on a short-arm centrifuge and under terrestrial gravity. Twelve rowing athletes (4 women, aged 27.2 ± 7.4 years, height 179 ± 0.1 cm, mass 73.7 ± 9.4 kg) participated in two rowing sessions, spaced at least six weeks apart. One session used a short-arm centrifuge with +0.5 Gz, while the other inclined the rowing ergometer by 26.6° to mimic centrifugal loading. Participants started self-paced rowing at 30 W, increasing by 15 W every three minutes until exhaustion. We measured rowing performance, heart rate, blood pressure, ground reaction forces, leg muscle activation, and blood lactate concentration. Rowing on the centrifuge was well-tolerated without adverse events. No significant differences in heart rate, blood pressure, or blood lactate concentration were observed between conditions. Inclined rowing under artificial gravity resulted in lower power output (−33%, p < 0.001) compared to natural gravity, but produced higher mean and peak ground reaction forces (p < 0.0001) and increased leg muscle activation. Muscle activation and ground reaction forces varied with rotational direction. Rowing in artificial gravity shows promise as a strategy against cardiovascular and muscular deconditioning during long-term spaceflight, but further investigation is required to understand its long-term effects.

Dissociated cerebellar contributions to feedforward gait adaptation

The cerebellum is important for motor adaptation. Lesions to the vestibulo-cerebellum selectively cause gait ataxia. Here we investigate how such damage affects locomotor adaptation when performing the ‘broken escalator’ paradigm. Following an auditory cue, participants were required to step from the fixed surface onto a moving platform (akin to an airport travellator). The experiment included three conditions: 10 stationary (BEFORE), 15 moving (MOVING) and 10 stationary (AFTER) trials. We assessed both behavioural (gait approach velocity and trunk sway after stepping onto the moving platform) and neuromuscular outcomes (lower leg muscle activity, EMG). Unlike controls, cerebellar patients showed reduced after-effects (AFTER trials) with respect to gait approach velocity and leg EMG activity. However, patients with cerebellar damage maintain the ability to learn the trunk movement required to maximise stability after stepping onto the moving platform (i.e., reactive postural behaviours). Importantly, our findings reveal that these patients could even initiate these behaviours in a feedforward manner, leading to an after-effect. These findings reveal that the cerebellum is crucial for feedforward locomotor control, but that adaptive locomotor behaviours learned via feedback (i.e., reactive) mechanisms may be preserved following cerebellum damage.

Shoe sole impedes leg muscle activation and impairs dynamic balance responding to a standing-slip

The shoe sole is identified as a fall risk factor since it may impede the afferent information about the outside world collected by the plantar sensory units. However, no study has directly quantified how the shoe sole compromises body balance and increases fall risk. This study aimed to inspect how the sole affects human balance after an unexpected standing-slip. It was hypothesized that individuals wearing the sole, relative to their barefoot counterparts, would exhibit 1) more impaired stability and 2) disrupted lower limb muscle activation following a standing-slip. Twenty young adults were evenly randomized into two groups: soled and barefoot. The soled group wore a pair of customized 10-mm thick soles, while the other group was bare-footed. Full-body kinematics and leg muscle electromyography (EMG) were collected during a standardized and unexpected standing-slip. The EMG electrodes were placed on the tibialis anterior, gastrocnemius, rectus femoris, and biceps femoris bilaterally. Dynamic stability, spatiotemporal gait parameters, and the EMG latency of the leg muscles were compared between groups. The sole impeded the initiation of the recovery step possibly because it interfered with the accurate detection of the external perturbation and subsequently activated the leg muscles later in the soled group than in the barefoot group. As a result, individuals in the soled group experienced a longer slip distance and were more unstable than the barefoot group at the recovery foot liftoff. The findings of this study could augment our understanding of how the shoe sole impairs body balance and increases the fall risk.

The metabolic effects of habitual leg shaking: A randomized crossover trial.

The adverse effects of sedentary behavior on obesity and chronic diseases are well established. However, the prevalence of sedentary behavior has increased, with only a minority of individuals meeting the recommended physical activity guidelines. This study aimed to investigate whether habitual leg shaking, a behavior traditionally considered unfavorable, could serve as an effective strategy to improve energy metabolism. A randomized crossover study was conducted, involving 15 participants (mean [SD] age, 25.4 [3.6]; mean [SD] body mass index, 22 [3]; 7 women [46.7%]). The study design involved a randomized sequence of sitting and leg shaking conditions, with each condition lasting for 20 min. Energy expenditure, respiratory rate, oxygen saturation, and other relevant variables were measured during each condition. Compared to sitting, leg shaking significantly increased total energy expenditure [1.088 kj/min, 95% confidence interval, 0.69-1.487 kj/min], primarily through elevated carbohydrate oxidation. The average metabolic equivalent during leg shaking exhibited a significant increase from 1.5 to 1.8. Leg shaking also raised respiratory rate, minute ventilation, and blood oxygen saturation levels, while having no obvious impact on heart rate or blood pressure. Electromyography data confirmed predominant activation of lower leg muscles and without increased muscle fatigue. Intriguingly, a significant correlation was observed between the increased energy expenditure and both the frequency of leg shaking and the muscle mass of the legs. Our study provides evidence that habitual leg shaking can boost overall energy expenditure by approximately 16.3%. This simple and feasible approach offers a convenient way to enhance physical activity levels.

The amount of lower leg muscle and physical activity in patients with postural tachycardia syndrome

Background: Resistance training for leg muscles is recommended for patients with postural tachycardia syndrome (POTS). However, no study has characterized the relationships between orthostatic symptoms, heart rate (HR) increase, and the mass of the lower leg muscle in patients with POTS. We sought to determine the relationships between the mass of the lower leg muscle, HR increase during the head-up tilt (HUT) test, and orthostatic symptoms in patients with POTS.Methods: We prospectively enrolled 42 patients with POTS who were older than 16 years. The muscle mass was estimated using bioelectrical impedance analysis. We used the International Physical Activity Questionnaire-Short Form to measure self-reported physical activity. All patients were asked to complete the Korean version of the Orthostatic Grading Scale (KOGS).Results: The HR increased during the HUT test by 38.7±7.88 beats/minutes. Both the HR increase during the HUT test and the total KOGS score were negatively correlated with the total metabolic equivalent of the task. The leg circumference and muscle mass were not correlated with the HR increase during the HUT test or the KOGS score.Conclusions: The leg circumference and muscle mass were not related to orthostatic symptoms in patients with POTS. Cardiac remodeling or blood volume increase may be responsible for improvement in POTS after physical activity.

Influence of oral motor tasks on postural muscle activity during dynamic reactive balance.

Jaw clenching improves dynamic reactive balance on an oscillating platform during forward acceleration and is associated with decreased mean sway speed of different body regions. It is suggested that jaw clenching as a concurrent muscle activity facilitates human motor excitability, increasing the neural drive to distal muscles. The underlying mechanism behind this phenomenon was studied based on leg and trunk muscle activity (iEMG) and co-contraction ratio (CCR). Forty-eight physically active and healthy adults were assigned to three groups, performing three oral motor tasks (jaw clenching, tongue pressing against the palate or habitual lower jaw position) during a dynamic one-legged stance reactive balance task on an oscillating platform. The iEMG and CCR of posture-relevant muscles and muscle pairs were analysed during platform forward acceleration. Tongue pressing caused an adjustment of co-contraction patterns of distal muscle groups based on changes in biomechanical coupling between the head and trunk during static balancing at the beginning of the experiment. Neither iEMG nor CCR measurement helped detect a general neuromuscular effect of jaw clenching on the dynamic reactive balance. The findings might indicate the existence of robust fixed patterns of rapid postural responses during the important initial phases of balance recovery.

Lower leg muscle activation during the ebbets foot drills

Lateral ankle sprains (LAS) often lead to chronic ankle instability (CAI). The Ebbets foot drills were created to strengthen the lower leg muscles and reduce the risk of LAS. The current study aimed to explore the activation of the lower leg muscles during the Ebbets foot drills. Twenty-two (22) college students without LAS participated in the study. Surface electromyography (sEMG) of the tibialis anterior (TA), tibialis posterior (TP), and peroneus longus (PL) was collected during each of the Ebbets foot drills and a normal walking trial. The sEMG mean root mean square (RMS) was calculated for each walking and Ebbets foot drill trial duration. The mean RMS was higher during the Ebbets foot drills compared to normal walking for all muscles. The TA sEMG mean RMS was greater (4.0–68.3%, P = 0.001–0.023) during all the Ebbets foot drills than during the walking trial. The TP had greater mean RMS during the toe-in (50.4%, P < 0.001), toe-out (55.0%, P < 0.001), and backward walking (47.3%, P < 0.001) drills, than during the walking trial. The PL had greater mean RMS during all Ebbets foot drills (19.4–53.7%, P < 0.001) except for the heel walking and inversion drills. Ebbets foot drills higher muscle activity than regular walking, suggesting that the Ebbets foot drills could aid in the strengthening of the TA, TP, and PL muscles. These results build evidence on Ebbets’ theory and indicate that these drills may be used to rehabilitate LAS and CAI.

Treadmill running: how long before soft-tissue vibrations reach a steady state?

The aim of this study was to determine whether a steady state was reached over time in soft-tissue vibrations (STV) when running with different midsole hardness. Kinematics, kinetics and electromyography changes were also investigated in an attempt to be as comprehensive as possible. Forty-five physically active adults (17 females) with experience in treadmill running performed an 8.5 minutes trial at a self-selected speed with soft, medium and hard midsoles. STV of gastrocnemius muscle, kinetics, kinematics and electromyographic activity of gastrocnemius muscle and tibialis anterior were recorded for 30 seconds at minutes 0, 2, 4, 6 and 8. No time effects were found for STV, passive peak, loading rate and leg muscle activity. No significant footwear × time interactions were observed, suggesting that familiarisation is independent of midsole hardness. The fastest adjustments were an increase of foot inversion and active peak within the first 4 minutes respectively before reaching a steady state. Step frequency and vertical stiffness decreased and plateaued at minute 6. Duty factor and contact time increased whereas flight time decreased during the entire running trial. Results indicate that a familiarisation to midsole hardness is not needed for STV reliable measurements. Depending on the other biomechanical parameters assessed, we recommend at least a 6-minute running trial and a longer running trial for contact and flight times assessment.

Effects of a passive upper-body exoskeleton on whole-body kinematics, leg muscle activity, and discomfort during a carrying task.

To compare whole-body kinematics, leg muscle activity, and discomfort while performing a 10-min carrying task with and without a passive upper-body exoskeleton (CarrySuitⓇ), for both males and females. Diverse commercial passive exoskeletons have appeared on the market claiming to assist lifting or carrying task. However, evidence of their impact on kinematics, muscle activity, and discomfort while performing these tasks are necessary to determine their benefits and/or limitations. Sixteen females and fourteen males carried a 15kg load with and without a passive exoskeleton during 10-min over a round trip route, in two non-consecutive days. Whole-body kinematics and leg muscle activity were evaluated for each condition. In addition, leg discomfort ratings were quantified before and immediately after the task. The gastrocnemius and vastus lateralis muscle activity remained constant over the task with the exoskeleton. Without the exoskeleton a small decrease of gastrocnemius median activation was observed regardless of sex, and a small increase in static vastus lateralis activation was observed only for females. Several differences in sagittal, frontal, and transverse movements' ranges of motion were found between conditions and over the task. With the exoskeleton, ROM in the sagittal plane increased over time for the right ankle and pelvis for both sexes, and knees for males only. Thorax ROMs in the three planes were higher for females only when using the exoskeleton. Leg discomfort was lower with the exoskeleton than without. The results revealed a positive impact on range of motion, leg muscle activity, and discomfort of the tested exoskeleton.

Evaluation of EMG patterns in children during assisted walking in the exoskeleton.

While exoskeleton technology is becoming more and more common for gait rehabilitation in children with neurological disorders, evaluation of gait performance still faces challenges and concerns. The reasoning behind evaluating the spinal locomotor output is that, while exoskeleton's guidance forces create the desired walking kinematics, they also affect sensorimotor interactions, which may lead to an abnormal spatiotemporal integration of activity in particular spinal segments and the risk of abnormalities in gait recovery. Therefore, traditional indicators based on kinematic or kinetic characteristics for optimizing exoskeleton controllers for gait rehabilitation may be supplemented by performance measures associated with the neural control mechanisms. The purpose of this study on a sample of children was to determine the basic features of lower limb muscle activity and to implement a method for assessing the neuromechanics of spinal locomotor output during exoskeleton-assisted gait. To this end, we assessed the effects of a robotic exoskeleton (ExoAtlet Bambini) on gait performance, by recording electromyographic activity of leg muscles and analyzing the corresponding spinal motor pool output. A slower walking setting (about 0.2 m/s) was chosen on the exoskeleton. The results showed that, even with slower walking, the level of muscle activation was roughly comparable during exoskeleton-assisted gait and normal walking. This suggests that, despite full assistance for leg movements, the child's locomotor controllers can interpret step-related afferent information promoting essential activity in leg muscles. This is most likely explained by the active nature of stepping in the exoskeleton (the child was not fully relaxed, experienced full foot loading and needed to maintain the upper trunk posture). In terms of the general muscle activity patterns, we identified notable variations for the proximal leg muscles, coactivation of the lumbar and sacral motor pools, and weak propulsion from the distal extensors at push-off. These changes led to the lack of characteristic lumbosacral oscillations of the center of motoneuron activity, normally associated with the pendulum mechanism of bipedal walking. This work shows promise as a useful technique for analyzing exoskeleton performance to help children develop their natural gait pattern and to guide system optimization in the future for inclusion into clinical care.

The effect of prolonged walking on leg muscle activity patterns and vulnerability to perturbations

Understanding the consequences and ecological relevance of muscle fatigue is important to guide the development of strategies to preserve independence. However, few studies have examined walking-related fatigue and the effects on walking instability. Our purpose was to investigate the effects of prolonged walking on leg muscle activity and vulnerability to balance perturbations. Eighteen healthy young adults completed a 30-min walking trial at their preferred walking speed while leg muscle activities were recorded. Before and after the 30-min walk, participants responded to five 5% body weight lateral force perturbations. Time-frequency analysis with wavelet transformation and principal component analyses assessed neuromuscular adaptations of muscles to prolonged walking. Following prolonged walking, we observed a time-dependent increase in EMG intensities at slower frequencies for the soleus and tibialis anterior and a decrease in mean amplitudes for the soleus, lateral gastrocnemius, and semitendinosus. Mean mediolateral CoM displacement following perturbations averaged 21% larger after the 30-min walk. Our results suggest that walking for 30 min at a comfortable speed elicits complex neuromuscular adaptations indicative of local muscle fatigue and an increased vulnerability to walking balance perturbations. These findings could inform fatigue monitoring systems or walking assistive devices aimed at reducing walking-related fatigue and maintaining independent mobility.