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

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).

This study is a secondary analysis of a multicenter randomized controlled trial.

Inpatients of 2 specialized neurorehabilitation hospitals.

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.

After randomization, individuals were allocated to conventional, virtual reality, or robot-assisted treatment groups (20 sessions, 1 h/d, 5 d/wk, 4wk).

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.

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).

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.