Electromyographic analyses of global synkinesis in the paretic upper limb after stroke

Background and Purpose. Global synkinesis (GS), or motor irradiation, is an involuntary movement associated with the coactivation of numerous muscles in one limb when the opposite limb is active. The electromyographic (EMG) patterns of people with stroke and people who were healthy were analyzed to characterize GS development in relation to joint involvement and to attempt to relate these findings to clinical observations. Subjects and Methods. Twenty patients with stroke, divided into 2 groups with either greater levels of irradiation (SG, n = 10) or lesser levels of irradiation (SL, n= 10), and 20 subjects in a control group were studied. A dynamometer was used to provide resistance for voluntary isometric muscle contractions of the flexor muscle groups of the shoulder, elbow, and wrist. The summated and standardized net EMG amplitudes of 8 principal muscles of the unexercised (paretic) upper extremity were used to characterize intensity and spatial representation of GS. Clinical measurements included the Fugl-Meyer Assessment Scale (FMA), Barthel Index of Activities of Daily Living (BI), and the stage on the Brunnström Stages of Motor Recovery Scale (BR). Results. In the SG and control groups, a more substantial GS intensity was associated with muscle contractions of the flexor muscles of the opposite proximal joint than was the case for contractions of the flexor muscles of the distal joint, whereas such a gradient change was absent in the SL group. The corresponding spatial patterns of GS exhibited a predominant cross-excitation over the unexercised pectoralis major and extensor carpi radialis muscles in the control group, contrary to the enhanced activation of the brachioradialis and biceps brachii muscles noted in patients with stroke. The SG group had a better FMA score and a more satisfactory BR stage than did the SL group, and the 2 neurological scores were related to GS intensity for patients with stroke, depending on joint involvement. Discussion and Conclusion. Intensity of GS provided an affiliation with motor deficits and a promising window for poststroke recovery mechanisms.