Muscle activity during gait initiation in normal elderly people

The purpose of this study was to describe the patterns of phasic muscle during gait initiation in normal elderly people. Bilateral surface EMG recordings were made of tibialis anterior, medial gastrocnemius and gluteus medius activity throughout gait initiation in 21 subjects. A variable expression of the onset muscle pattern is shown, with a tendency for muscle activity to be more variable in the preparatory phase. These results provide a baseline of normal gait initiation muscle activity against which to compare that of patients with gait initiation and balance difficulties.     

Changes in gait associated with acute stage II posterior tibial tendon dysfunction

The purpose of this study was to examine differences in gait mechanics between patients with acute stage II PTTD and healthy volunteers. Hindfoot and midfoot kinematics, plantar foot pressures and electromyographic (EMG) activity of the posterior tibialis, gastrocnemius, anterior tibialis and the peroneals were measured in five patients with acute stage II PTTD. Kinematics and kinetics were compared to a database of 20 healthy volunteers. EMG and plantar pressure data were obtained from five healthy volunteers. Hindfoot moments and powers were also calculated. The center of pressure excursion index (CPEI) was calculated from the plantar pressures. Significant differences were observed between the two groups, which confirmed clinical observations. Limited hindfoot eversion and increased midfoot external rotation occurred during the first and third rockers. The EMG data suggested that tendon dysfunction in the posterior tibialis is associated with compensatory activity, not only in its antagonists (the peroneals), but also in the anterior tibialis and the gastrocnemius. These data suggest that non-operative treatment of patients with PTTD should consider minimizing the activity of the posterior tibialis as well as the peroneals, the anterior tibialis and the gastrocnemius.     

Principles underlying the organization of movement initiation from quiet stance.

The purpose of this study was to determine common principles underlying the programming of movement initiation from quiet stance. Subjects were asked to initiate gait, step over a ruler, or to step over a 10 cm high obstacle at a self-paced speed and as fast as possible. The independent variables were initiation condition (gait initiation, stepping over a ruler or obstacle) and initiation speed (self-paced and as fast as possible). The dependent measures for the stance limb only were the latency between postural soleus (S(1)) EMG inhibition and tibialis anterior (TA) EMG onset, the duration of both TA and soleus (S(2)) activity following TA, duration and slope, impulse, and peak forces of the anterior-posterior (Fx) ground reaction force. Selected timing events were also monitored. Analysis of variance was used to determine main and interaction effects. The following results were obtained. (1) The interval from the inhibition of S(1) postural activity to the onset of TA remained invariant between all conditions. (2) The duration of TA increased and S(2) decreased with an increase in speed of initiation. There was no difference in TA and S(2) duration between the initiation conditions. (3) Time to heel-off remained invariant for all conditions. (4) Prior to heel-off all force variables increased with initiation speed but were similar between initiation conditions. After heel-off force variables were different between speeds and conditions being greater for fast speed and stepping over the obstacle. Two conclusions may be drawn from this study. First, the results indicate that gait initiation consists of two, highly coordinated motor programs. Heel-off of the stance limb is the division between these two programs. Second, our findings also suggest that gait initiation and stepping are governed by the same motor programs.     

Electromyographic changes of agonist and antagonist calf muscles during maximum isometric induced fatigue

The purpose of this study was to examine electromyographic changes of the agonist and antagonist muscles during fatigue. Nine healthy, untrained subjects exerted a maximum voluntary heel lifting contraction with their dominant limb. The EMG activity over the soleus and the tibialis anterior muscles was recorded during the contraction. The results showed that the torque output during heel lifting and the soleus EMG activity decreased, whereas the tibialis anterior EMG revealed a small but non-significant decrease. However, the ratio of the tibialis anterior to the soleus EMG increased significantly at the end of the fatigue protocol, a fact that reveals that the decrease rate of the antagonist's activity was significantly lower than the decrease rate of the agonist activity. It is concluded that during a maximal fatigue protocol, both the agonist and antagonist muscle activity may decline, however, the slower rate of antagonist's activity decrease relative to the agonist's activity is a finding that requires further investigation. This finding may reflect a higher level of agonist and antagonist muscle co-activation and probably a relatively higher opposing torque from the antagonist muscles at the end of the fatigue session.     

Gait characteristics of children and youth with chemotherapy induced peripheral neuropathy following treatment for acute lymphoblastic leukemia

Sensory changes and muscle weakness attributable to chemotherapy induced peripheral neuropathy (CIPN) are possible sequela of treatment for acute lymphoblastic leukemia (ALL) which can result in long-lasting difficulties with walking. The purpose of this study was to describe the gait characteristics of children and youth treated for ALL who exhibited CIPN compared to typically developing children and youth using 3D motion analyses and electromyography (EMG). Temporal-spatial, kinematic, kinetic, and electromyographic (EMG) data were collected from 17 youth (mean age 11.2 (5.7) years) with CIPN and compared to data from 10 typically developing youth. Although the gait of the CIPN group was heterogeneous between and within participants, the CIPN group demonstrated primary deviations attributable to CIPN and secondary deviations, both passive effects and active compensatory mechanisms. They had significantly less peak hip extension, knee flexion in loading, dorsiflexion at initial contact, plantarflexion at pre-swing, and dorsiflexion in swing, shorter step lengths, and lower ankle moments and powers than the comparison participants. EMG data from the gastrocnemius and tibialis anterior muscles showed excessive co-activation and atypical firing including out of phase firing of the gastrocnemius in late swing and loading and premature firing of the tibialis anterior in terminal stance. This study, using 3D motion analysis and EMG in youth with CIPN, showed variability in gait suggesting that clinical decision-making should be based on a detailed understanding of individual impairments and associated gait abnormalities.     

Motor adaptation during dorsiflexion-assisted walking with a powered orthosis

A robotic ankle-foot orthosis (AFO) that provides powered assistance could adjust to varying gait dynamics much better than a rigid AFO. To provide insight into how humans would adapt to a powered AFO, we studied the response of neurologically intact subjects walking with an active dorsiflexion assist orthosis proportionally controlled by tibialis anterior electromyography (EMG). We examined the two mechanical functions of ankle dorsiflexors in gait (power absorption at heel strike and power generation at toe-off) by recruiting two groups of healthy subjects: Group One, called Continuous Control (n=5), had dorsiflexion assistance both at the initial heel contact and during swing; Group Two, called Swing Control (n=5), had the assistance only during swing. We hypothesized both groups of subjects would reduce tibialis anterior EMG amplitude with practice walking with the powered dorsiflexion assist. Ten healthy subjects were fitted with custom-made orthoses that included an artificial pneumatic muscle providing dorsiflexor torque. We collected lower body kinematics, EMG, and artificial muscle force while subjects walked on a treadmill for two 30-min training sessions. We found that subjects walked with increased ankle dorsiflexion by 9 degrees but showed different adaptation responses of the two tibialis anterior EMG bursts. The first EMG burst around heel strike had approximately 28% lower amplitudes (p<0.05) but the second EMG burst during swing had similar amplitudes. These results provide baseline data of EMG controlled dorsiflexion assist in neurologically intact humans that can be used to guide future studies on neurologically impaired individuals.     

Effects of changing the initial horizontal location of the center of mass on the anticipatory postural adjustments and task performance associated with step initiation

The aim of this study was to elucidate whether and how the duration and/or amplitude parameters of anticipatory postural adjustments (APAs) affected the task performance in a single step forward from differences in the initial horizontal location of CoM. Ten male subjects performed initiation of a single step forward with the right swing leg with strict regulation of the step length at three initial body positions (Sw, step initiation from a 50% position of the center of pressure (CoP) shift in the maximum lateral right side; N, step initiation from the upright position at rest; St, step initiation from a 50% position of the CoP shift in the maximum lateral left side). The duration required for stepping from the heel-off to foot-contact of the swing leg (step time) in the Sw condition was significantly shorter than of the other two conditions. The APAs durations in the Sw condition was significantly longer than in the other two conditions. In the Sw condition, the durations of the anticipatory electromyographic (EMG) activities of the tibialis anteriors (TA) of the swing leg correlated significantly with mechanical parameters (the displacement of the CoM, velocity of the CoM, and propulsive force) in the anticipatory phase, while the mean amplitudes of the anticipatory EMG activities of the TA of the swing leg did not correlate significantly with mechanical parameters in the anticipatory phase.

The present results suggest that the duration parameters of the APAs associated with single step forward motion are dependent on the displacement of the CoM estimated by the initial cutaneous messages from the swing leg prior to initiation of the single step, and that the APAs may be directly involved not only in the increase in propulsive force towards the supporting leg, but also increasing the forward propulsive force at heel-off.     

Effects of changing the initial horizontal location of the center of mass on the anticipatory postural adjustments and task performance associated with step initiation

The aim of this study was to elucidate whether and how the duration and/or amplitude parameters of anticipatory postural adjustments (APAs) affected the task performance in a single step forward from differences in the initial horizontal location of CoM. Ten male subjects performed initiation of a single step forward with the right swing leg with strict regulation of the step length at three initial body positions (Sw, step initiation from a 50% position of the center of pressure (CoP) shift in the maximum lateral right side; N, step initiation from the upright position at rest; St, step initiation from a 50% position of the CoP shift in the maximum lateral left side). The duration required for stepping from the heel-off to foot-contact of the swing leg (step time) in the Sw condition was significantly shorter than of the other two conditions. The APAs durations in the Sw condition was significantly longer than in the other two conditions. In the Sw condition, the durations of the anticipatory electromyographic (EMG) activities of the tibialis anteriors (TA) of the swing leg correlated significantly with mechanical parameters (the displacement of the CoM, velocity of the CoM, and propulsive force) in the anticipatory phase, while the mean amplitudes of the anticipatory EMG activities of the TA of the swing leg did not correlate significantly with mechanical parameters in the anticipatory phase.The present results suggest that the duration parameters of the APAs associated with single step forward motion are dependent on the displacement of the CoM estimated by the initial cutaneous messages from the swing leg prior to initiation of the single step, and that the APAs may be directly involved not only in the increase in propulsive force towards the supporting leg, but also increasing the forward propulsive force at heel-off.     

A method for quantifying dynamic muscle dysfunction in children and young adults with cerebral palsy

Cerebral palsy (CP) is caused by a lesion to the brain resulting in adaptations to the structure and function of the muscles and compromised mobility. Spastic cerebral palsy is commonly assessed by the limb kinematics and kinetics measured in a gait laboratory. However, these measures do not directly quantify the patterns of muscle dysfunction that occur during movements. Recent studies have shown that electromyographic (EMG) signals from children with CP have abnormal magnitude, timing and frequency content. Here we demonstrate how wavelet decomposition of the EMG signals into time-frequency space coupled to principal component analysis of the EMG spectra can be used as a powerful tool to quantify the patterns of muscle dysfunction. Data were compared between 17 children with spastic diplegic CP and 36 asymptomatic controls for the rectus femoris, semimembranosus, medial gastrocnemius and tibialis anterior muscles. CP muscle generated higher mean EMG frequencies. Imbalances in activity between the tibialis anterior and medial gatrocnemius contributed to equinus ankle during the swing phase. Patterns of co-activations between antagonistic muscles differed between CP and asymptomatic patients and were EMG frequency dependent. Muscle dysfunction was greater in the distal compared to the proximal lower limb. Muscle dysfunction between the tibialis anterior and medial gastrocnemius was distinguished with 96% sensitivity at 95% specificity.     

Changes in muscle activation patterns when running step rate is increased

Running with a step rate 5-10% greater than one's preferred can substantially reduce lower extremity joint moments and powers, and has been suggested as a possible strategy to aid in running injury management. The purpose of this study was to examine how neuromuscular activity changes with an increase in step rate during running. Forty-five injury-free, recreational runners participated in this study. Three-dimensional motion, ground reaction forces, and electromyography (EMG) of 8 muscles (rectus femoris, vastus lateralis, medial gastrocnemius, tibialis anterior, medial and lateral hamstrings, and gluteus medius and maximus) were recorded as each subject ran at their preferred speed for three different step rate conditions: preferred, +5% and +10% of preferred. Outcome measures included mean normalized EMG activity for each muscle at specific periods during the gait cycle. Muscle activities were found to predominantly increase during late swing, with no significant change in activities during the loading response. This increased muscle activity in anticipation of foot-ground contact likely alters the landing posture of the limb and the subsequent negative work performed by the joints during stance phase. Further, the increased activity observed in the gluteus maximus and medius suggests running with a greater step rate may have therapeutic benefits to those with anterior knee pain.     

Effect of plantar desensitization on postural adjustments prior to step initiation

Plantar cutaneous afferent provides information about the contact between the body and the support surface and could affect the anticipatory postural adjustments (APAs). This study investigated the effect of plantar desensitization on the APAs for step initiation. Twenty-five healthy young adults participated in this study and were instructed to begin walking as fast as possible under 4 plantar desensitization conditions, none (NoneD), and desensitization of the stepping, supporting or bilateral (BilD) plantar surfaces, with eyes open or closed. The desensitization was achieved by cold water immersion of the plantar surface for 15 min. Foot switches recorded the timing of the stepping events. Surface electromyography (EMG) recorded the activation of bilateral tibialis anterior. The center of pressure (COP) and ground reaction force (GRF) data were derived from the force platform on which the subject initiated walking. The results showed that during the anticipation phase, the peak COP displacement toward the stepping leg was significantly smaller in BilD than in unilateral desensitization, which in turn was smaller than in NoneD, regardless of vision. The time to reach the peak COP displacement was significantly sooner with plantar desensitization in the eyes open condition. The GRF, EMG and anteroposterior COP displacement or the timing of the stepping events was not affected by plantar desensitization. These findings indicate that plantar cutaneous afferent contributed to the control of the APAs for step initiation by scaling the displacement of the mediolateral COP displacement and loss of its sensitivity could not be compensated by visual inputs.     

Compensatory movements following gait perturbations: changes in cinematic and muscular activation patterns

The present study was designed to investigate the neuronal control and biomechanical effects of stumbling reactions. To induce these perturbations, a specially prepared treadmill was used which allowed rapid and powerful changes of treadmill speed. EMG recordings of leg muscles were related to cinematic movement patterns. Following an accelerating impulse, the standing leg was displaced in a posterior direction compared with normal gait, with a premature touchdown of the contralateral, swinging leg, forward of the body axis. This was associated with simultaneous activation of the gastrocnemius and biceps femoris of the ipsilateral and the tibialis anterior muscles of the contralateral leg. Following deceleration, the standing leg was displaced in an anterior direction and the contralateral swinging leg touched the ground prematurely behind the body axis. This was associated with activation of the ipsilateral tibialis anterior and rectus femoris and contralateral tibialis anterior muscles. In both conditions, the activation of the lower leg muscles on both sides occurred with a latency of 60-70 ms, monosynaptic responses being absent. In both cases, early touchdown was associated with a forward extension of the arm. It is concluded that the EMG responses are mediated by a polysynaptic spinal pathway to keep the body center of gravity constant and to prevent falling.     

An electromyographic analysis of obligatory (hemiplegic cerebral palsy) and voluntary (normal) unilateral toe-walking

This study compares lower extremity muscle activation during gait in patients with hemiplegic cerebral palsy (CP) with healthy subjects mimicking the patients. The purpose was to understand the differences between obligatory toe-walking as observed in hemiplegic CP gait and voluntary toe-walking. The results contribute to a better understanding by distinguishing between primary deviations in muscle activity as a direct consequence of the underlying neurological pathology of hemiplegic CP and secondary, compensatory deviations due to the biomechanics of toe-walking. Surface electromyographic (EMG), kinematic and kinetic data were compared between a group of 12 hemiplegic CP patients and a group of 10 healthy subjects walking normally and when mimicking hemiplegic gait. Integrated 3D gait analysis was performed with simultaneous EMG recordings of the medial gastrocnemius, tibialis anterior, rectus femoris, and semitendinosus muscles bilaterally. The EMG pattern of the toe-walking leg in the mimicking subjects was modified in gastrocnemius and tibialis anterior as compared with normal gait. This modified muscle activation pattern showed strong similarities to that of the patients and therefore can be regarded, at least in part, as activity required for toe-walking. A possible primary gait abnormality was observed in the rectus femoris where the patients showed a burst of EMG activity in mid-swing phase in contrast to the mimicking subjects who showed normal EMG during this phase.     

Variation in neuromuscular responses during acute whole-body vibration exercise

PURPOSE: Leg muscle strength and power are increased after whole-body vibration (WBV) exercise. These effects may result from increased neuromuscular activation during WBV; however, previous studies of neuromuscular responses during WBV have not accounted for motion artifact. METHODS: Sixteen healthy adults performed a series of static and dynamic unloaded squats with and without two different directions of WBV (rotational vibration, RV; and vertical vibration, VV; 30 Hz; 4 mmp-p). Activation of unilateral vastus lateralis, biceps femoris, gastrocnemius, and tibialis anterior was recorded using EMG. During RV and VV, increases in EMG relative to baseline were compared over a range of knee angles, contraction types (concentric, eccentric, isometric), and squatting types (static, dynamic). RESULTS: After removing large, vibration-induced artifacts from EMG data using digital band-stop filters, neuromuscular activation of all four muscles increased significantly (P相似文献   

Muscle coordination and function during cutting movements

PURPOSE: The objectives of this study were to: 1) establish a database of kinematic and EMG data during cutting movements, 2) describe normal muscle function and coordination of 12 lower extremity muscles during cutting movements susceptible to ankle sprains, and 3) identify potential muscle coordination deficiencies that may lead to ankle sprain injuries. METHODS: Kinematic, EMG, and GRF data were collected from 10 recreationally active male subjects during both a side-shuffle and v-cut movement. RESULTS: The data showed that muscles functioned similarly during both movements. The primary function of the hip and knee extensors was to decelerate the center-of-mass during landing and to provide propulsion during toe-off. The hip add/abductors functioned primarily to stabilize the hip rather than provide mechanical power. The ankle plantar flexors functioned to provide propulsion during toe-off, and the gastrocnemius had an additional burst of activity to plantarflex the foot before touchdown during the side-shuffle to help absorb the impact. The tibialis anterior functioned differently during each movement: to dorsiflex and supinate the foot after toe-off in preparation for the next step cycle during the side-shuffle and to dorsiflex the foot before impact to provide the heel-down landing and ankle stability in the stance phase during the v-cut. CONCLUSIONS: The muscles crossing the ankle joint, especially the tibialis anterior and peroneus longus, may play an important role to prevent ankle sprain injuries. Both muscles provided stability about the subtalar joint by preventing excessive joint rotations. Future theoretical studies with forward dynamic simulations incorporating individual muscle actuators are needed to quantify the segment accelerations induced by active muscles which may prevent or lead to ankle sprain injuries.     

Intramuscular pressure and torque during isometric, concentric and eccentric muscular activity

Intramuscular pressures, electromyography (EMG) and torque generation during isometric, concentric and eccentric maximal isokinetic muscle activity were recorded in 10 healthy volunteers. Pressure and EMG activity were continuously and simultaneously measured side by side in the tibialis anterior and soleus muscles. Ankle joint torque and position were monitored continuously by an isokinetic dynamometer during plantar flexion and dorsiflexion of the foot. The increased force generation during eccentric muscular activity, compared with other muscular activity, was not accompanied by higher intramuscular pressure. Thus, this study demonstrated that eccentric muscular activity generated higher torque values for each increment of intramuscular pressure. Intramuscular pressures during antagonistic co-activation were significantly higher in the tibialis anterior muscle (42–46% of maximal agonistic activity) compared with the soleus muscle (12–29% of maximal agonistic activity) and was largely due to active recruitment of muscle fibers. In summary, eccentric muscular activity creates higher torque values with no additional increase of the intramuscular pressure compared with concentric and isometric muscular activity.     

Ankle function during hopping in subjects with functional instability of the ankle joint

A common mechanism of inversion injury involves a lateral movement producing a hypersupination of the ankle joint. To date, no study has investigated patterns of muscle activity, three-dimensional (3D) joint kinematics and kinetics simultaneously in a group of subjects with functional instability (FI) compared with a non-injured control group during a lateral hopping test. Twenty-six subjects with the subjective complaint of FI of the ankle joint and 24 non-injured healthy control subjects volunteered to participate in the study. We measured 3D lower limb kinematics, kinetics and surface electromyography (EMG) of the rectus femoris, tibialis anterior, peroneus longus and soleus muscle in all subjects during a lateral hop task for the period 200 ms pre- and post-initial contact (IC). FI subjects were observed to have a less-everted position of the ankle joint during the time period from 45 ms pre-IC to 95 ms post-IC (P<0.05). FI subjects were also found to have an increase in pre- and post-IC rectus femoris, tibialis anterior and solues EMG activity. The results suggest that subjects with FI exhibit changes in ankle joint movement and neuromuscular control that could predispose to further injury.     

Measuring cortical motor hemodynamics during assisted stepping – An fNIRS feasibility study of using a walker

Walkers are commonly prescribed worldwide to individuals unable to walk independently. Walker usage leads to improved postural control and voluntary movement during step. In the present study, we aimed to provide a concept-proof on the feasibility of an event-related protocol integrating the analyses of biomechanical variables of step initiation and functional near-infrared spectroscopy (fNIRS) to measure activation of the supplementary motor area (SMA) while using a walker. Healthy young participants were tested while stepping with versus without the use of the walker. Behavioral analysis showed that anticipatory postural adjustments (APA) decreased when supporting the body weight on the walker. Delta (without–with) of activation magnitude of the muscle tibialis anterior was positively correlated to the delta of deoxyhemoglobin concentration changes in the SMA. The novelty of this study is the development of a protocol to assess brain function together with biomechanical analysis during the use of a walker. The method sheds light to the potential utility of combining fNIRS and biomechanical assessment during assistive step initiation, which can represent a new opportunity to study populations with mobility deficits.     

Stretch- and H-reflexes of the lower leg during whole body cooling and local warming

BACKGROUND: This study was undertaken to evaluate if possible changes in stretch- and H-reflexes could be related to the changes in the EMG activity of the cooled lower leg muscles observed during a stretch-shortening cycle exercise. METHODS: Eight subjects wearing shorts and jogging shoes were exposed once to 27 degrees C and twice to 10 degrees C for 60 min each. During the second exposure to 10 degrees C, the subject's lower legs were kept warm (10 degrees Clw) with electrical pillows. After the exposures Achilles tendon reflex (stretch reflex) was induced and the EMG activity of the triceps surae was measured. Immediately after reflex measurements the EMG activity of the triceps surae and tibialis anterior during a drop-jump (stretch-shortening cycle) was measured. After similar thermal exposures electrically induced H-reflex from the calf was measured. RESULTS: During the preactivity and stretch phases the EMG activity of the triceps surae increased after the exposure to 10 degrees C, whereas during the shortening phase it decreased. During the shortening phase cooling, on the contrary, increased the activity of tibialis surae anterior. These changes disappeared at 10 degrees Clw. At 10 degrees C the maximum EMG-amplitude of triceps surae during stretch reflex decreased (p<0.05), reflecting suppressed muscle spindle activity. Suppressed spindle activity causes the agonist to be unfacilitated and the antagonist muscle contraction to be uninhibited, which was seen in the present study as decreased agonist and increased antagonist EMG activity during the shortening phase at 10 degrees C. The Hmax/Mmax-ratio, H-reflex latency and amplitude increased at 10 degrees C (p<0.05), reflecting increased motoneuron pool excitability. This in part may explain the increased EMG activity during the preactivity and stretch phases. CONCLUSION: Cooling-induced increase in the excitability of the motoneuron pool and suppression of muscle spindle activity seem to be responsible of the EMG activity changes during the stretch-shortening cycle, consequently decreasing muscular performance.