Involuntary contralateral upper extremity muscle activation pattern during unilateral pinch grip following stroke

Study design: Repeated measures design. Introduction: Mirror activity refers to emergence of motion not only in the intended, but also in the contralateral limb. Purpose: To characterize post-stroke mirror activities across multiple muscles during unilateral pinch. Methods: Chronic stroke survivors performed unilateral pinch grip using the paretic and nonparetic hand, while four muscles' EMGs were recorded for both hands. Results: During the paretic hand grip, the relaxed nonparetic hand showed mirror activity that was more pronounced for the intrinsic (FDI and thenar eminence) than extrinsic muscles (FDS and EDC). During the nonparetic hand grip, mirror activity in the paretic hand was suppressed for the intrinsic than extrinsic muscles. Conclusion: Chronic stroke survivors' relaxed hand did not mirror the task hand's muscle activation pattern, but displayed altered muscle activation patterns depending on muscles and sides, possibly mediated by disturbed interhemispheric inhibition and relative reliance on corticospinal tracts among muscles. Level of evidence: N/A. (C) 2013 Hanley & Belfus, an imprint of Elsevier Inc. All rights reserved.