Changing patterns of postural hip muscle activity during recovery from stroke

Objective: To describe the recovery of neurophysiological responses to perturbation of standing balance after stroke. Methods: Surface electromyography (EMG) from hip abductors and adductors and ground reaction forces (GRF) were measured in response to 20 sideways pushes applied to the pelvis by a linear motor. Each subject's data from pushes 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 could 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 contralateral muscles, (3) an appropriate, if delayed, response in the hemiparetic abductor but not adductor muscles, and (4) a relatively normal pattern in both hemiparetic muscles. Nine of 13 patients showed a change in pattern of hip muscle activity during recovery. All patients who initially resisted the sideways pushes solely with muscles of the unaffected leg later regained use of the hemiparetic hip abductors Conclusions: The pattern of hip muscle activation changed towards normal during recovery from stroke in most patients. Use of compensatory strategies early after stroke in these subjects did not prevent return of normal patterns of muscle activation later.