Effects of ankle exoskeleton assistance during human walking on lower limb muscle contractions and coordination patterns / 生物医学工程学杂志

Lower limb ankle exoskeletons have been used to improve walking efficiency and assist the elderly and patients with motor dysfunction in daily activities or rehabilitation training, while the assistance patterns may influence the wearer's lower limb muscle activities and coordination patterns. In this paper, we aim to evaluate the effects of different ankle exoskeleton assistance patterns on wearer's lower limb muscle activities and coordination patterns. A tethered ankle exoskeleton with nine assistance patterns that combined with differenet actuation timing values and torque magnitude levels was used to assist human walking. Lower limb muscle surface electromyography signals were collected from 7 participants walking on a treadmill at a speed of 1.25 m/s. Results showed that the soleus muscle activities were significantly reduced during assisted walking. In one assistance pattern with peak time in 49% of stride and peak torque at 0.7 N·m/kg, the soleus muscle activity was decreased by (38.5 ± 10.8)%. Compared with actuation timing, the assistance torque magnitude had a more significant influence on soleus muscle activity. In all assistance patterns, the eight lower limb muscle activities could be decomposed to five basic muscle synergies. The muscle synergies changed little under assistance with appropriate actuation timing and torque magnitude. Besides, co-contraction indexs of soleus and tibialis anterior, rectus femoris and semitendinosus under exoskeleton assistance were higher than normal walking. Our results are expected to help to understand how healthy wearers adjust their neuromuscular control mechanisms to adapt to different exoskeleton assistance patterns, and provide reference to select appropriate assistance to improve walking efficiency.

Surface electromyographic examination of the coordination of the spastic upper limb muscles of stroke survivors / 中华物理医学与康复杂志

Objective To explore any changes in the surface electromyography (sEMG) signals measured on the spastic upper limb muscles of stroke parents during maximum isometric voluntary contraction and to analyze any abnormal synergy patterns quantitatively in order to design better rehabilitation programs for developing coordination.Methods Ten stroke survivors with hemiparesis were selected into a patient group and ten healthy counterparts were recruited into a control group.sEMG signals were recorded bilaterally from the flexor carpi ulnaris (FCU),biceps brachii (BB),triceps brachii (TB) and deltoid (D) during maximum isometric voluntary contractions involving wrist flexion and extension,elbow flexion and extension,and shoulder abduction.The two groups' co-contraction ratios (CR) and co-activation ratios were calculated and compared.Results During elbow flexion and extension the average CR of the BB on the affected side was significantly higher than that on the unaffected side and also significantly higher than the control group average.The average CR of the TB on the affected side was significantly higher than that of the healthy controls.In all cases the average CR of the BB was larger than that of the TB.The difference in CR between the TB and the BB on the affected side was significantly larger than on the unaffected side and the control group average.During elbow flexion,the co-activation ratio of the FCU,TB and D on the affected side was significantly higher than on the unaffected side and among the healthy controls,and the co-activation ratio of the FCU on the affected side was significantly higher than that of the D and TB.During elbow extension,the co-activation ratio of the FCU,BB and D on the affected side was significantly higher in the same way,and the co-activation ratio of the FCU on the affected side was again significantly higher than that of the D and BB.During wrist flexion,the average co-activation ratio of the BB and D on the affected side was significantly greater than that on the unaffected side and among the healthy controls,and the co-activation ratio of the BB on the affected side was significantly higher than that of the D and TB.During shoulder abduction,the co-activation ratio of the BB on the affected side was significantly larger than on the unaffected side and among the healthy controls.Conclusion After a stroke the upper limbs often show flexor spasticity and abnormal synergy patterns.Rehabilitation strategy should be adopted to tackle these so as to enhance overall limb coordination.

Lower extremity muscle coordination in stroke patients revealed by surface electromyography / 中华物理医学与康复杂志

Objective To explore the changes in muscle activity patterns in the lower leg during ankle dorsiflexion and plantarflexion in stroke patients. Methods Ten recovering stroke patients with hemiparesis(Pa- tient group)and ten age-and sex-matched healthy volunteers(Healthy control group)were studied.The subjects performed ankle dorsiflexion and plantarflexion synchronized with a visual cue while supine.Surface electrodes were applied over the anterior tibialis(TA),caput laterale musculi gastrocnemius(IGM),caput mediale musculi gas-troenemius(mGM)and soleus muscles(SOL)for integrated electromyography(iEMG).Results During ankle dorsiflexion,the TA,lGM,mGM and SOL of the affected side showed a significantly lower iEMG signal than the unaffected side.Activity of the lGM,mGM and SOL of the affected side were significantly lower than in the healthy controls.During ankle plantaflexion,the TA,lGM and mGM on the affected side had significantly lower activity than those of the healthy controls.The mGM of the affected side showed significantly lower muscle activity than the unaffeeted side.The SOL contraction ratio on the affected side was significantly higher than on the unaffected side and in the healthy control group. Conclusion Except for the soleus,there is an obvious decline in muscle activi-ty in the affected lower extremities of stoke patients during ankle dorsiflexion and plantaflexion.The soleus on the affected side becomes the primary plantarflexor in patients with stroke,rather than the caput laterale musculi gas-trocnemius or caput mediale musculi gastroenemius as in healthy subjects.

Thigh muscle function in stroke patients revealed by velocity-encoded cine phase-contrast MRI / 中华物理医学与康复杂志

Objective To examine how stroke affects muscle coordination and whether muscle function will be improved after rehabilitation.Methods Ten stroke patients with mild hemiparesis and six age-and sex-matched controls were investigated at baseline.Velocity-encoded phase-contrast magnetic resonance imaging (VE-PC MRI) and surface eleetromyography (sEMG) were performed to evaluate muscle coordination of thigh muscles during knee extension and flexion and the effect of rehabilitation. Results Using VE-PC MRI,we found that the peak velocity of rectus femoris was lower in the affected limb (P