Changing patterns of postural hip muscle activity during recovery from stroke

Objective: To describe the recovery of neurophysiological responses to pert urbation of standing balance after stroke. Methods: Surface electromyography (EMG) from hip abductors and adductors an d ground reaction forces (GRF) were measured in response to 20 sideways pus hes applied to the pelvis by a linear motor. Each subject's data from pushe s in each direction were averaged and the presence of a muscle EMG response was assessed visually. Subjects: Thirteen acute hemiplegic patients were tested as soon as they co uld stand after stroke [median six weeks) and serially during recovery. Results: Four patterns of hip muscle activity were seen: (1) no response at all, (2) no response in hemiparetic muscles but compensation by contralate ral muscles, (3) an appropriate, if delayed, response in the hemiparetic ab ductor but not adductor muscles, and (4) a relatively normal pattern in bot h hemiparetic muscles. Nine of 13 patients showed a change in pattern of hi p muscle activity during recovery. All patients who initially resisted the sideways pushes solely with muscles of the unaffected leg later regained us e of the hemiparetic hip abductors Conclusions: The pattern of hip muscle activation changed towards normal du ring recovery from stroke in most patients. Use of compensatory strategies early after stroke in these subjects did not prevent return of normal patte rns of muscle activation later.