Function of leg muscles acting on foot as modified by body movements

¹ Detroit Orthopaedic Clinic, Detroit, Michigan

Leg muscles acting on the foot as a supporting base were recorded electromyographically from normal young adults during selected postural movements. Surface electrodes picked up action potentials simultaneously from the tibialis anterior and posterior, extensor digitorum longus, peroneus longus and brevis, gastrocnemius, soleus, and flexor digitorum longus. Motion pictures and photographs of the various procedures were taken to assist in analysis of changes in body position during activity. These activities included postural changes, shifting body weight, and resisting external forces applied to the upper trunk. Movements initiated in the trunk, which automatically changed position of the leg on the foot, may or may not modify the magnitude of action potentials evoked in those muscles which contract during relaxed standing. To resist gravitational or external forces, the multijointed upper segments realign to assist the foot in maintaining its position as a supporting base. The majority of activities performed by the head, trunk, upper extremities, and pelvis produced changes in position of the leg on the foot which are automatic and seldom brought into the field of conscious control.