Determination of muscle activation in upper limb during gait among stroke patients with homolateral limb synkinesis: a cross-sectional analytical pilot study.

Post-stroke neural damage can impair sequential muscle activation, which may lead to associated reactions (ARs) during effortful tasks. During gait this may manifest as homolateral limb synkinesis (HLS), where voluntary movement of paretic limb evokes involuntary movement in the corresponding ipsilateral limb. Upper limb muscle activation underlying HLS during ambulation remains poorly understood, hence this study aimed to investigate muscle activation using surface electromyography (sEMG) in post-stroke HLS patients. This study included 22 participants, 11 in each group. sEMG recordings were obtained from four agonist-antagonist muscle pairs of affected upper limb in stroke participants and dominant limb in controls during a 10-m gait trial at self-selected pace. sEMG signals were normalised to a reference contraction. Group comparisons were performed using Mann-Whitney U test, followed by false discovery rate (FDR) correction for multiple comparisons. Initial analyses demonstrated significantly greater normalised activation in pectoralis major, middle deltoid, biceps brachii, extensor carpi radialis brevis, and flexor carpi ulnaris among HLS participants, which after FDR persisted only in biceps brachii, extensor carpi radialis brevis, and flexor carpi ulnaris. HLS during gait involves abnormal activation of predominantly the elbow and wrist musculature, with non-rhythmic aberrant muscle activity in proximal and distal muscles compared to controls.