Muscle Synergy Analysis for Clinical Characterization of Upper Limb Motor Recovery After Stroke

Objective: To characterize individuals with stroke who responded or did not respond to upper limb motor treatment by analyzing muscle synergy patterns (similarity, merging, and fractionation). Design: This study is a secondary analysis of a multicenter randomized controlled trial. Setting: Inpatients of 2 specialized neurorehabilitation hospitals. Participants: We enrolled individuals (N=62) with a unilateral first-event ischemic or hemorrhagic stroke and severe-to-mild upper limb motor impairment (Fugl-Meyer Assessment-Upper Extremity score of 5-61, of 66). We excluded people with untreated seizure, severe cognitive, or verbal comprehension impairment. Interventions: After randomization, individuals were allocated to conventional, virtual reality, or robot-assisted treatment groups (20 sessions, 1 h/d, 5 d/wk, 4wk). Main outcome measures: A blinded assessor performed assessments both before and after the intervention. Surface electromyography recordings from 16 muscles during reaching tasks were collected pre- and post-treatment. We extracted muscle synergy patterns (similarity, merging, and fractionation) of the stroke-affected and unaffected upper limb of each subject. Results: Overall, individuals improved upper limb motor function (Fugl-Meyer Assessment-Upper Extremity change score=7.14±7.46; P<.001). We identified 34 responders to treatment showing clinically significant improvement (over the Minimal Clinically Important Difference of 5 points on the Fugl-Meyer Assessment-Upper Extremity). The responders showed decreased merging of synergies (P=.016) as compared with the non-responders (P=.025), who conversely showed improved similarity of synergies (P=.006). Conclusions: In individuals with stroke undergoing upper limb motor rehabilitation, changes in the synergy merging pattern may serve as a potential marker to distinguish responders from non-responders.