Flexor Activity Research Articles

Peculiarities of Activation of the Upper Limb Muscles in Humans during Realization of Two-Joint Movements

Coordination of the activity of flexors and extensors of the shoulder and elbow joints during realization of slow cyclic two-joint movements by the upper limb of the tested subjects was examined; the above movements were performed within the horizontal plane. The subject tracked the trajectory of the command signal shown on a monitor. Test movements corresponded to circular shifts of a handle; there were initiated in either clockwise (Lcw) or counterclockwise (Lccw) directions. An external loading could be also applied in the above directions (Mcw and Mccw, respectively). Surface (integral) EEGs were recorded from eight muscles of the upper limb and shoulder belt. As was found, the EMG amplitudes at opposite directions of tracking the target trajectory were dissimilar. At the clockwise direction of the external loading, the EMG amplitudes of most examined muscles during the counterclockwise movement were higher than those shown during the clockwise movement. Parameters of EMGs depended on the mechanical parameters of the movement. Under Mccw conditions, shorter loading waves act upon flexors of both joints, while longer waves act upon extensors. The situation is opposite under Mcw conditions (longer waves influence the flexors, while shorter waves act on the extensors).

Differences in flexor and extensor activity during locomotor-related leg movements in chick embryos.

Prior to hatching, chick embryos spontaneously produce repetitive limb movements (RLMs), a developmental precursor to walking. During RLMs, flexor and extensor muscles are alternately active as during stance and swing phases of gait. However, previous studies of RLMs observed that flexor muscles were rhythmically active for many cycles, whereas extensors often failed to be recruited. Thus, we asked if flexor muscles are preferentially recruited during RLMs in chick embryos 1 day before hatching and onset of walking. Using a within-subject design, we compared EMG burst parameters for flexor and extensor muscles acting at the hip or ankle. Findings indicated that flexor burst count exceeded extensor count. Also, flexor muscles were consistently recruited at the lowest levels of neural drive. We conclude that there is a bias favoring flexor muscle recruitment and drive during spontaneously produced RLMs. Potential neural mechanisms and developmental implications of our findings are discussed.

Active Trigger Points in the Cervical Musculature Determine the Altered Activation of Superficial Neck and Extensor Muscles in Women With Migraine.

Previous studies have demonstrated the presence of active trigger points (TrPs) in women with migraine reproducing their headache attacks. No study has investigated whether these TrPs can alter cervical muscle function in migraine. Our objective was to analyze differences in the activation of superficial neck flexor and extensor muscles in women with migraine considering the presence of active TrPs in the splenius capitis (SC), the upper trapezius (UT), and the sternocleidomastoid (SCM) muscles. Surface electromyography (EMG) was recorded from the superficial flexors (SCM and anterior scalene) and the extensor (SC, UT) muscles bilaterally as participants performed a staged task of cranio-cervical flexion (CCF; 5 contractions representing a progressive increase in CCF range of motion) in 70 women with migraine. They were stratified according to the presence or the absence of active TrPs in the SCM, the SC, or the UT musculature. A comparison of EMG normalized root mean square (RMS) values was conducted with a 2×5 analysis of covariance with the task level as the within-subject variable, group stratified by active TrPs as the between-subjects variable and the presence of neck pain as a covariable. All patients exhibited active TrPs in their cervical muscles, which reproduced their migraine. Women with migraine exhibiting active TrPs in the SCM (P<0.01), the UT (P<0.05), or the SC (P<0.05) muscles had lower normalized RMS values of their superficial neck flexors than those without active TrPs in the same muscles. In addition, individuals exhibiting active TrPs in the SC and the UT (both, P<0.05) muscles had higher normalized RMS values in the SC muscle than those without active TrPs in the same muscles. The presence of active TrPs in the cervical musculature determines an altered activation of superficial neck and extensor muscles during low-load, isometric CCF contractions in women with migraine.

Neck and Shoulder Muscle Activation Among Experienced and Inexperienced Pilots in +Gz Exposure.

The aim of the present study was to compare differences in electromyography (EMG) activation of the neck and shoulder muscles between groups of inexperienced and experienced pilots during controlled +Gz exposure in a centrifuge. The subjects were volunteer cadets (inexperienced group) and lieutenants (experienced group) undergoing their first centrifuge training. The first group did not have any high performance aircraft (HPA) experience, while the latter one had a 1-yr experience of intense flying of HPA. During the centrifuge run, EMG activity was recorded from the left and right shoulder, neck flexor, and neck extensor muscles. The pilots without HPA experience had significantly higher muscle activity in the neck flexor and extensor muscles during the last 5 s of the recorded period at G levels exceeding +7.4. Muscle activity in the neck and shoulder muscles was gradually higher among the whole study group with increasing +Gz forces. Because pilots without any HPA experience had significantly higher muscle activity than their counterparts with experience of HPA, we suppose that the experience of high +Gz forces might lead to lower muscle activation in the same flight mission.Honkanen T, Oksa J, Mäntysaari MJ, Kyröläinen H, Avela J. Neck and shoulder muscle activation among experienced and inexperienced pilots in +Gz exposure. Aerosp Med Hum Perform. 2017; 88(2):90-95.

Effects of manipulation of the thorax and intensity of the pressure biofeedback unit on the superficial cervical flexors muscle during craniocervical flexion exercise

[Purpose] This study examined the effects of manipulation of the thorax and the intensity of the pressure biofeedback unit on the superficial cervical flexors muscle during craniocervical flexion exercise. [Subjects and Methods] Thirty three subjects participated in the experiment. Thirty three healthy people without any orthopedic history were also selected. The subjects could monitor the pressure applied to cervical vertebra 3 of the craniocervical junction by markings on the pressure biofeedback unit. Craniocervical flexion exercise was performed for 20 seconds per pressure, and two minutes of rest was allowed after exercise to reduce muscle fatigue. [Results] Significant differences in the post-training gains in the sternocleidomastoid and scalene were observed between the thorax fixation group and thorax non-fixation group. The thorax fixation group showed that muscle activation of the sternocleidomastoid and scalene was increased when the pressure biofeedback unit intensity was 40 mmHg than when pressure biofeedback unit intensity was 20 mmHg and 30 mmHg in the post-hoc result. The thorax non-fixation group showed that muscle activation of the sternocleidomastoid and scalene was higher when the pressure biofeedback unit intensity was 40mmHg compared to that when the pressure biofeedback unit intensity was 20mmHg in the post-hoc result. [Conclusion] Craniocervical flexion exercise is a clinically effective method that reduces the superficial neck flexor muscle activation.

Single-stage reconstruction of high-voltage electric burns sequelae of volar forearm using nerve grafts, short tendon grafts and microvascular flap

Introduction: A total of 10 patients underwent single-stage reconstruction of high-voltage electrical burn sequelae at the distal forearm and volar wrist, in patients with complete loss of motor and sensory function of the hand; all 10 were operated using interposition tendon grafts for the flexor digitorum profundus, nerve grafts for the median and ulnar nerves and the anterolateral thigh flap (ALT) for coverage; in addition, the fascial component of the flap was used to wrap the repaired finger flexors. Materials and Methods: All the flaps survived, and eight of the 10 patients had S3 or S4 recovery of median nerve sensation. Results: The final outcome measurement was done by adopting a variant of the abbreviated upper extremity functional index. The mean value for this was 19 of a possible 40 points (range in 10 patients −7 to 28). Discussion: Single-stage reconstruction using short tendon grafts and nerve grafts is a useful procedure in high-voltage electrical burns. Conclusion: The use of the ALT with vascularised fascia permits early finger flexor activity suitable for activities of daily living.

Shear and pressure under the first ray in neuropathic diabetic patients: Implications for support of the longitudinal arch

ObjectiveTo assess dynamic arch support in diabetic patients at risk for Charcot neuroarthopathy whose arch index has not yet shown overt signs of foot collapse. MethodsTwo indirect measures of toe flexor activation (ratios: peak hallux pressure to peak metatarsal pressure – Ph/Pm; peak posterior hallux shear to peak posterior metatarsal shear – Sh/Sm) were obtained with a custom built system for measuring shear and pressure on the plantar surface of the foot during gait. In addition, the tendency of the longitudinal arch to flatten was measured by quantifying the difference in shear between the 1st metatarsal head and the heel (Sflatten) during the first half of the stance phase. Four stance phases from the same foot for 29 participants (16 control and 13 neuropathic diabetic) were assessed. ResultsThe peak load ratio under the hallux (Ph/Pm) was significantly higher in the control group (2.10±1.08 versus 1.13±0.74, p=0.033). Similarly, Sh/Sm was significantly higher in the control group (1.87±0.88 versus 0.88±0.45, p=0.004). The difference in anterior shear under the first metatarsal head and posterior shear under the lateral heel (Sflatten) was significantly higher in the diabetic group (p<0.01). Together these findings demonstrate reduced plantar flexor activity in the musculature responsible for maintaining the longitudinal arch. ConclusionsWith no significant difference in arch index between the two groups, but significant differences in Ph/Pm, Sh/Sm and Sflatten the collective results suggest there are changes in muscle activity that precede arch collapse.

Effect of a novel teat preparation system on upper extremity muscle activity among U.S. large-herd dairy parlor workers

BackgroundDairy production in the U.S. is moving towards large-herd milking operations resulting in an increase in task specialization and work demands. Large-herd dairy parlor workers experience a high prevalence of musculoskeletal symptoms in the upper extremity. The purpose of this study is to evaluate the effects of an alternative teat scrubber (TS) cow preparation method on upper extremity muscle activity among large-herd parlor workers, as well compare to muscle activity associated with conventional manual milking tasks. MethodsUpper extremity muscle activity was recorded among U.S. large-herd parlor workers (n = 15) using surface electromyography. Participants performed multiple task cycles, using both conventional and TS methods. Muscle activity levels were then compared across conventional manual and TS milking tasks. ResultsConventional manual milking tasks of dip, strip and wipe were associated higher muscle activity levels of the upper trapezius and anterior deltoid. Biceps muscle activity was greatest during teat dip and wipe. Forearm flexor and extensor muscle activity was greatest during teat wipe and dip. The TS system resulted in more desirable anterior deltoid EMG profiles, and less desirable biceps, forearm flexor and extensor profiles. ConclusionsResults suggest that the TS system is effective in reducing anterior deltoid muscle activation levels. The TS system also appears to result in increased biceps, forearm flexor and extensor muscle activation levels. Increases in muscle activation levels could be offset by reduced repetitiveness resulting from three conventional manual milking tasks being replaced with one TS task. Relevance to industryIf parlor production requirements (e.g., quality and onsistency) are maintained while simultaneously reducing cumulative muscle loading and worker fatigue, then TS use should be considered in milking parlor operations.

Beta-band activity and connectivity in sensorimotor and parietal cortex are important for accurate motor performance

Accurate motor performance may depend on the scaling of distinct oscillatory activity within the motor cortex and effective neural communication between the motor cortex and other brain areas. Oscillatory activity within the beta-band (13–30Hz) has been suggested to provide distinct functional roles for attention and sensorimotor control, yet it remains unclear how beta-band and other oscillatory activity within and between cortical regions is coordinated to enhance motor performance. We explore this open issue by simultaneously measuring high-density cortical activity and elbow flexor and extensor neuromuscular activity during ballistic movements, and manipulating error using high and low visual gain across three target distances. Compared with low visual gain, high visual gain decreased movement errors at each distance. Group analyses in 3D source-space revealed increased theta-, alpha-, and beta-band desynchronization of the contralateral motor cortex and medial parietal cortex in high visual gain conditions and this corresponded to reduced movement error. Dynamic causal modeling was used to compute connectivity between motor cortex and parietal cortex. Analyses revealed that gain affected the directionally-specific connectivity across broadband frequencies from parietal to sensorimotor cortex but not from sensorimotor cortex to parietal cortex. These new findings provide support for the interpretation that broad-band oscillations in theta, alpha, and beta frequency bands within sensorimotor and parietal cortex coordinate to facilitate accurate upper limb movement. Summary statementOur findings establish a link between sensorimotor oscillations in the context of online motor performance in common source space across subjects. Specifically, the extent and distinct role of medial parietal cortex to sensorimotor beta connectivity and local domain broadband activity combine in a time and frequency manner to assist ballistic movements. These findings can serve as a model to examine whether similar source space EEG dynamics exhibit different time-frequency changes in individuals with neurological disorders that cause movement errors.

Spastic co-contractions of hemiparetic patients: Which rehabilitation to improve gait?

During rehabilitation of hemiparetic patients, physiotherapists face a discrepancy between motor skills during analytical exercises and functional abilities observed during gait. A muscle recruitment difference in the two situations could explain this gap. Among pathologic motricity manifestations observed in hemiparetic patients (Gracies 2005), exist the spastic co contraction phenomenon that presently concerned our work. Indeed, the main objective of this study was to compare co-contractions in hemiparetic subjects between an analytical exercise modality and a functional exercise modality, i.e. gait. Our hypothesis was that the co contraction is increased during gait as compared to an analytical exercise and could consequently lead to a decrease of gait ability in patients. Muscular activity of knee flexors and extensors was recorded by surface EMG in analytic exercises and during the swing phase of gait, in a group of hemiparetic subjects (SH) and a group of healthy subjects (SS). Co-contraction index in duration and in magnitude was calculated from EMG data and allowed us the comparison between the 2 exercise modalities. Twelve SH and 11 SS were included. ICC differed between analytical and functional modalities in SH ( P < 0.05). Discussion: the observed results show a significant difference between co-contractions observed analytically and during gait in SH. These results validate the initial hypothesis since in most cases, co-contractions are increased during gait. If the conditions of muscle recruitment differ in analytic conditions and during gait, it seems unsuited to propose analytical exercises with the aim to improve gait parameters. This finding therefore suggests a more functional rehabilitation, according to the concept of task-oriented training: rehabilitate gait by gait.

Motor fatigability after low-intensity hand grip exercises in persons with multiple sclerosis

IntroductionDuring maximal, sustained contractions, persons with multiple sclerosis (PwMS) show higher motor fatigability in comparison with healthy persons. It is not known if motor fatigability is also different between PwMS and healthy persons during low-intensity exercises. Thus, the aim of this study was to determine the difference in hand grip fatigability between healthy persons and PwMS for both hands during low-intensity hand grip exercises. Methods19 PwMS and 19 healthy controls performed 18min of hand grip exercises at a maximum of 25% of the maximal voluntary strength, with an electronic hand dynamometer. Perceived fatigability, maximal hand grip strength and muscle activity (electromyography) of the wrist flexors and extensors were recorded in between these exercises for the dominant and non-dominant hand. Results and discussionThere was a significant decrease in maximal hand grip strength after exercising in both groups and for both hands, mainly situated in the first 6min. In contrast to what was hypothesized, PwMS did not show more decline in strength than healthy controls, neither in the dominant nor the non-dominant hand. There was no group difference in the increase of the perceived fatigability in the dominant hand. However, for the non-dominant hand, the perceived fatigability after exercising increased more in PwMS than in healthy controls. Additionally, there was no relation between fatigue indices, as assessed with short maximal contractions and the strength decline after low-intensity repetitive exercises.

A robotic exoskeleton to treat crouch gait from cerebral palsy: Initial kinematic and neuromuscular evaluation.

A robotic exoskeleton was designed for individuals with crouch gait caused by cerebral palsy with the intent to supplement existing muscle function during walking. The aim of this study was to evaluate how powered knee extension assistance provided during stance and swing phases of the gait cycle affect knee kinematics, and knee flexor and extensor muscle activity. Muscle activity and kinematic data were collected from four individuals with crouch gait from cerebral palsy during their normal walking condition and while walking with the exoskeleton under stance, swing, and stance & swing assistance. The exoskeleton was effective in reducing crouch by an average of 13.8° in three of the four participants when assistance was provided during the stance phase; assistance during the swing phase alone was ineffective. Peak knee extensor activity was maintained for all of the conditions during the stance and swing phases. Integrated (i.e. area under the curve) knee extensor activity decreased in two of the subjects indicating a more well-modulated activation pattern. Modest increases in peak and integrated antagonist knee flexor activity were exhibited in all participants; the subject without kinematic improvement had the greatest increase. While the exoskeleton was well tolerated, additional training with a focus on reducing knee flexor activity may lead to further improvements in crouch gait reduction.

Hand rehabilitation after stroke using a wearable, high DOF, spring powered exoskeleton.

Stroke patients often have inappropriate finger flexor activation and finger extensor weakness, which makes it difficult to open their affected hand for functional grasp. The goal was to develop a passive, lightweight, wearable device to enable improved hand function during performance of activities of daily living. The device, HandSOME II, assists with opening the patient's hand using 11 elastic actuators that apply extension torques to finger and thumb joints. Device design and initial testing are described. A novel mechanical design applies forces orthogonal to the finger segments despite the fact that all of the device DOFs are not aligned with human joint DOF. In initial testing with seven stroke subjects with impaired hand function, use of HandSOME II significantly increased maximum extension angles and range of motion in all of the index finger joints (P<;0.05). HandSOME II allows performance of all the grip patterns used in daily activities and can be used as part of home-based therapy programs.

Upslope treadmill exercise enhances motor axon regeneration but not functional recovery following peripheral nerve injury.

Following peripheral nerve injury, moderate daily exercise conducted on a level treadmill results in enhanced axon regeneration and modest improvements in functional recovery. If the exercise is conducted on an upwardly inclined treadmill, even more motor axons regenerate successfully and reinnervate muscle targets. Whether this increased motor axon regeneration also results in greater improvement in functional recovery from sciatic nerve injury was studied. Axon regeneration and muscle reinnervation were studied in Lewis rats over an 11 wk postinjury period using stimulus evoked electromyographic (EMG) responses in the soleus muscle of awake animals. Motor axon regeneration and muscle reinnervation were enhanced in slope-trained rats. Direct muscle (M) responses reappeared faster in slope-trained animals than in other groups and ultimately were larger than untreated animals. The amplitude of monosynaptic H reflexes recorded from slope-trained rats remained significantly smaller than all other groups of animals for the duration of the study. The restoration of the amplitude and pattern of locomotor EMG activity in soleus and tibialis anterior and of hindblimb kinematics was studied during treadmill walking on different slopes. Slope-trained rats did not recover the ability to modulate the intensity of locomotor EMG activity with slope. Patterned EMG activity in flexor and extensor muscles was not noted in slope-trained rats. Neither hindblimb length nor limb orientation during level, upslope, or downslope walking was restored in slope-trained rats. Slope training enhanced motor axon regeneration but did not improve functional recovery following sciatic nerve transection and repair.

Influence of a 12.8-km military load carriage activity on lower limb gait mechanics and muscle activity

The high stress fracture occurrence in military populations has been associated with frequent load carriage activities. This study aimed to assess the influence of load carriage and of completing a load carriage training activity on gait characteristics. Thirty-two Royal Marine recruits completed a 12.8-km load carriage activity as part of their military training. Data were collected during walking in military boots, pre and post-activity, with and without the additional load (35.5 kg). Ground contact time, lower limb sagittal plane kinematics and kinetics, and electromyographic variables were obtained for each condition. When carrying load, there was increased ground contact time, increased joint flexion and joint moments, and increased plantar flexor and knee extensor muscle activity. Post-activity, there were no changes to kinematic variables, knee extensor moments were reduced, and there was evidence of plantar flexor muscle fatigue. The observed gait changes may be associated with stress fracture development.Practitioner Summary: This study identified gait changes due to load carriage and after a military load carriage training activity. Such activities are associated with lower limb stress fractures. A pre–post study design was used. Gait mechanics changed to a greater extent when carrying load, than after completion of the activity when assessed without load.

Organization of flexor-extensor interactions in the mammalian spinal cord: insights from computational modelling.

Alternation of flexor and extensor activity in the mammalian spinal cord is mediated by two classes of genetically identified inhibitory interneurons, V1 and V2b. The V1 interneurons are essential for high-speed locomotor activity. They secure flexor-extensor alternations in the intact cord but lose this function after hemisection, suggesting that they are activated by inputs from the contralateral side of the cord. The V2b interneurons are involved in flexor-extensor alternations in both intact cord and hemicords. We used a computational model of the spinal network, simulating the left and right rhythm-generating circuits interacting via several commissural pathways, and extended this model by incorporating V1 and V2b neuron populations involved in flexor-extensor interactions on each cord side. The model reproduces multiple experimental data on selective silencing and activation of V1 and/or V2b neurons and proposes the organization of their connectivity providing flexor-extensor alternation in the spinal cord. Alternating flexor and extensor activity represents the fundamental property underlying many motor behaviours including locomotion. During locomotion this alternation appears to arise in rhythm-generating circuits and transpires at all levels of the spinal cord including motoneurons. Recent studies in vitro and in vivo have shown that flexor-extensor alternation during locomotion involves two classes of genetically identified, inhibitory interneurons: V1 and V2b. Particularly, in the isolated mouse spinal cord, abrogation of neurotransmission derived by both V1 and V2b interneurons resulted in flexor-extensor synchronization, whereas selective inactivation of only one of these neuron types did not abolish flexor-extensor alternation. After hemisection, inactivation of only V2b interneurons led to the flexor-extensor synchronization, while inactivation of V1 interneurons did not affect flexor-extensor alternation. Moreover, optogenetic activation of V2b interneurons suppressed extensor-related activity, while similar activation of V1 interneurons suppressed both flexor and extensor oscillations. Here, we address these issues using the previously published computational model of spinal circuitry simulating bilateral interactions between left and right rhythm-generating circuits. In the present study, we incorporate V1 and V2b neuron populations on both sides of the cord to make them critically involved in flexor-extensor interactions. The model reproduces multiple experimental data on the effects of hemisection and selective silencing or activation of V1 and V2b neurons and suggests connectivity profiles of these neurons and their specific roles in left-right (V1) and flexor-extensor (both V2b and V1) interactions in the spinal cord that can be tested experimentally.

Patients with chronic, but not episodic, migraine display altered activity of their neck extensor muscles

The current study aimed to investigate differences in activity of neck flexor and extensor muscles in women with migraine considering the chronicity of their condition. Thirty-one subjects with episodic migraine, 21 with chronic migraine and 31 healthy controls participated. Surface electromyography signals were recorded bilaterally from the sternocleidomastoid, anterior scalene, splenius capitis and upper trapezius muscles as subjects performed 5 stages of cranio-cervical flexion (CCF), representing a progressive increase in range of CCF motion. Comparison of normalized root-mean-square among groups was conducted with 3×5 ANCOVA with task level as the within-subject variable, group as the between-subject variable, and the presence of neck pain and disability as co-variates. The group with chronic migraine exhibited increased activity of their extensor muscles compared to the control and episodic migraine groups (splenius capitis: F=3.149, P=0.045; upper trapezius: F=3.369, P=0.041). No significant between-group differences were found for the superficial neck flexors (sternocleidomastoid: F=1.161, P=0.320; anterior scalene: F=0.135, P=0.874). In conclusion, women with chronic migraine exhibit increased activity of their superficial neck extensor muscles when acting as antagonists during low-load isometric CCF contractions in comparison to non-headache subjects.

Does increased superficial neck flexor activity in the craniocervical flexion test reflect reduced deep flexor activity in people with neck pain?

BackgroundThe craniocervical flexion test assesses the deep cervical flexor muscles (longus capitis, longus colli). Ideally, electromyography (EMG) studies measure activity in both deep and superficial (sternocleidomastoid, anterior scalene) flexors during the test, but most studies confine recordings to superficial muscle activity as the technique to record the deep muscles is invasive. Higher activity of the superficial flexors has been interpreted as an indicator of reduced deep flexor activity in people with neck pain but how close the inverse relationship is during this test is unknown. MethodsEMG was recorded from the sternocleidomastoid, anterior scalene and deep cervical flexor muscles to quantify their relationship during the craniocervical flexion test, from 32 women (age: 38.0 ± 11.6 yrs) with a history of chronic non-specific neck pain. The range of craniocervical flexion at each of the five test stages was also measured. ResultsA moderate negative correlation was identified (r = −0.45; P < 0.01) between the average normalized EMG amplitude of the deep cervical flexors and sternocleidomastoid across all stages of the craniocervical flexion test. There was a moderate although weaker and non-significant negative correlation between deep cervical flexors and anterior scalene activity (r = −0.34; P = 0.053). ConclusionsThe results affirm the interpretation that higher levels of activity of the superficial flexor muscles are an indicator of reduced deep cervical flexor activity in the craniocervical flexion test. Further studies of neuromuscular and movement strategies used by people with neck pain to compensate for poorer activation of the deep cervical flexors will inform best clinical assessment.

Muscle Activity of the Lower Limb During Single-Legged Hopping

Running can be described as a series of bilateral single-legged jumps and landings; however, single-legged locomotion (SLL) is anecdotally more difficult than bi-lateral locomotion (BLL). Muscle activity may play a role in this increased difficulty; it is not known how active different muscles are during SLL vs. BLL, or whether providing body weight support during SLL would elicit more similar activity levels compared with BLL. PURPOSE: To compare muscle activity during single-legged locomotion at different levels of effective body weight (BW). METHODS: Subjects (n=12; 25.00±7.74 years, 1.67±0.09 m, 63.28±11.42 kg) performed running at 100% BW in addition to single-legged hopping at 80%, 70%, 60%, 50%, and 40% BW. Muscle activity of the Rectus Femoris, Semitendinosus, Tibialis Anterior, and Medial Gastrocnemius was measured. Average muscle activity was calculated over 15 seconds (zero offset removed, full-wave rectified). Activity from each muscle was analyzed using a one-way repeated measures analysis of variance (α=0.05). RESULTS: Muscle activity of the Semitendinosus and Tibialis Anterior was not affected by varying levels of effective BW (p>0.05). Muscle activity of the Rectus Femoris and Medial Gastrocnemius was influenced by varying levels of effective BW (p<0.05). For the Rectus Femoris, hopping at 80% BW and 70% BW elicited higher average muscle activity than running (92.4%; 70.8% increase, respectively), hopping at 60% BW (24.2%; 10.2%), hopping at 50% BW (39.9%; 24.2%), and hopping at 40% BW (62.5%; 44.3%). For the Gastrocnemius, hopping at 80% BW and 70% BW elicited higher average muscle activity than running (70.3%; 50.8% increase, respectively) and hopping at 40% BW (57.2%; 39.2%). CONCLUSIONS: It appears that increased knee flexor muscle activity is the primary mechanism that is responsible for why SLL is more difficult than BLL. Muscle activity between BLL and SLL at 50% BW were shown to be similar, which suggests the occurrence of a bilateral deficit. However, it is still unclear whether these increases are the result of the existence of a bilateral deficit, or a result of a change in the movement pattern.

Young, Healthy Subjects Can Reduce the Activity of Calf Muscles When Provided with EMG Biofeedback in Upright Stance.

Recent evidence suggests the minimization of muscular effort rather than of the size of bodily sway may be the primary, nervous system goal when regulating the human, standing posture. Different programs have been proposed for balance training; none however has been focused on the activation of postural muscles during standing. In this study we investigated the possibility of minimizing the activation of the calf muscles during standing through biofeedback. By providing subjects with an audio signal that varied in amplitude and frequency with the amplitude of surface electromyograms (EMG) recorded from different regions of the gastrocnemius and soleus muscles, we expected them to be able to minimize the level of muscle activation during standing without increasing the excursion of the center of pressure (CoP). CoP data and surface EMG from gastrocnemii, soleus and tibialis anterior muscles were obtained from 10 healthy participants while standing at ease and while standing with EMG biofeedback. Four sensitivities were used to test subjects' responsiveness to the EMG biofeedback. Compared with standing at ease, the two most sensitive feedback conditions induced a decrease in plantar flexor activity (~15%; P < 0.05) and an increase in tibialis anterior EMG (~10%; P < 0.05). Furthermore, CoP mean position significantly shifted backward (~30 mm). In contrast, the use of less sensitive EMG biofeedback resulted in a significant decrease in EMG activity of ankle plantar flexors with a marginal increase in TA activity compared with standing at ease. These changes were not accompanied by greater CoP displacements or significant changes in mean CoP position. Key results revealed subjects were able to keep standing stability while reducing the activity of gastrocnemius and soleus without loading their tibialis anterior muscle when standing with EMG biofeedback. These results may therefore posit the basis for the development of training protocols aimed at assisting subjects in more efficiently controlling leg muscle activity during standing.