Extrinsic muscle activity, foot motion and ankle joint moments during the stance phase of walking.

This study examined stance phase foot kinematics, kinetics and electromyographic (EMG) activity of extrinsic muscles of 18 healthy males. Three-dimensional kinematic and kinetic data were obtained via video analysis of surface markers and a force plate. Ankle joint moments are described about orthogonal axes in a segmental coordinate system. Kinematic data comprise rearfoot and forefoot motion, described about axes of a joint coordinate system, and medial longitudinal arch height. Surface EMG was obtained for tibialis anterior, soleus, gastocnemius medialis and lateralis, peroneus longus and peroneus brevis and extensor digitorum longus. It was concluded that the demands on the controlling muscles are greatest prior to foot flat and after heel rise. Tibialis anterior restrained rearfoot plantarflexion from heel contact to 10% stance, and eversion between 10% stance and footflat. Activity in peroneus longus was consistent with its role in causing eversion after heel contact, then as a stabiliser of the forefoot after heel rise. Activity in peroneus brevis suggested a role in restraining lateral rotation of the leg over the foot, late in stance.