Kinematic study of human ankle control during walking

Abstract

In order to determine the extent to which ankle motion is voluntarily controlled during walking, angular velocity measurements at the ankle were taken in two cases. In the first case, subjects were seated and instructed to move their ankle as quickly as possible in eight directions indicated by a computer program in dorsi- and plantar-flexion and inversion and eversion. In the second case, subjects were instructed to walk on a treadmill for thirty seconds at a normal pace, and at speeds that felt faster and slower than normal. Velocity measurements were made using an exoskeletal robot, called the Anklebot, originally designed for rehabilitation purposes. The electromyogram of anterior tibialis, peroneus longus, and gastrocnemius muscles was also recorded. Results showed that all subjects plantarflexed their foot at a higher velocity after heel-strike while walking than when moving at their maximum voluntary speed. This implies that this motion results in part from foot-ground interaction mediated by the mechanical impedance of the ankle and is not solely imposed by contraction of the gastrocnemius and other muscles. In contrast, results also showed that subjects were able to dorsiflex their foot at a higher velocity when moving at maximum voluntary speed than was observed after toe-off while walking.