Muscle Synergy Analysis for Stroke During Two Degrees of Freedom Reaching Task on Horizontal Plane

This study aimed to investigate muscle synergies from major muscles that contribute to each degree of freedom (DOF) in a low DOF task with trunk restraint during a fundamental reaching task used frequently in daily life. Seven non-patients (controls) and eleven stroke patients (mild or severe groups) in Brunnstrom stage 2–4 recovery were assessed. Subjects performed two DOF reaching tasks requiring motor coordination of the elbow and shoulder on the horizontal plane. Electromyography signals were measured during the task, and muscle synergy data extracted from them were analyzed using cluster analysis. No significant differences were noted between patients with stroke and healthy subjects in terms of the coefficient of determination, R-squared, determined according to the number of modules. Cluster analysis revealed that each of the clusters in the control and mild groups was governed by one channel. However, one cluster in the severe group was governed by two channels. When the clusters of the mild group and the control group were compared, the highest similarities (all values exceeded 0.9) were noted between the corresponding clusters of the two groups. All other similarity values were < 0.8. A similar trend was noted when the severe group clusters were compared with control group clusters; however, only three corresponding pairs of clusters exhibited similarity values exceeding 0.9, while the rest were < 0.8. Muscle synergies during the two DOF reaching tasks with trunk restraint showed differences in extensors between healthy individuals and patients with stroke.