Control of the medial-lateral balance in walking.

Eleven normal adults had their gait tested from the viewpoint of ground reaction force, myoelectric activity, and the motion of pronation-supination in the foot. There were marked differences in the myoelectric activity between the large lateral component force and the smaller one during the midstance phase. When the lateral component force was large, the pronation of the foot was small; the peroneus longus was active during the midstance phase; and the activity of the tibialis posterior disappeared earlier than in the small component. On the other hand, when the lateral component force was small, the pronation was large; the tibialis posterior, flexor digitorum longus, and extensor hallucis longus were all active; but the peroneus longus remained inactive during the midstance phase. Based on these findings, it is suggested that the leg muscles and the motion of the foot take part in controlling the medial lateral balance in walking.