Electromyographic responses of distal ankle musculature of standing hemiplegic patients to continuous anterior-posterior perturbations during imposed weight transfer over the affected leg

This study was undertaken to evaluate the influence of weight shift over the affected leg of standing hemiplegic patients on the electromyographic responses of the medial gastrocnemius and tibialis anterior muscles during continuous anterior-posterior movements of the base of support. Recordings were taken from 10 hemiplegic subjects and from 9 healthy subjects of comparable age. Each subject was first tested standing with both feet on a level surface and then with either leg (in healthy subjects) or the unaffected leg (in hemiplegic subjects) raised on a step. The second testing position caused unloading of the elevated leg and weight shift, that is, loading of the other leg. The measured variables were modulation of muscular activity, determined by a modulation index formulated for that purpose, and the relative amount of integrated electromyographic activity in each muscle. Changes in both variables in the uneven stance position as compared with even stance, occurred primarily in the unaffected (unloaded) leg in the hemiplegic subjects. These changes were comparable to changes in the unloaded leg of the healthy subjects. Thus, imposed loading on the affected leg of the hemiplegic subjects did not significantly improve either the reduced modulation or the relatively low IEMG activity of the investigated muscles. Further studies are required to evaluate the contribution of weight shift to recovery of postural responses in the affected leg of hemiplegic patients.