INFLUENCE OF EXTRINSIC PLANTAR FLEXORS ON FOREFOOT LOADING DURING HEEL RISE

This investigation studied the effects of simulated plantar flexor mus cle activity on forefoot loading using a static cadaver model. Nine ca daver feet were mounted in an apparatus in the heel rise position. Usi ng computer-controlled and pneumatic actuators, forces were simultaneo usly applied to the tendons of the triceps surae, flexor hallucis long us, flexor digitorum longus, peroneus brevis and longus, and tibialis posterior until 750 N of ground reaction force was achieved, at which time forefoot plantar pressure patterns were captured immediately with a pedobarograph. Second metatarsal bending moments were calculated fr om strain gauge data collected concurrently. Consecutive loading cycle s were performed with sequential elimination of simulated muscle force from each tendon except the Achilles. Loss of simulated flexor halluc is longus activity significantly decreased great toe contact forces an d significantly increased forces under the forefoot. Simulated loss of both the flexor hallucis longus and flexor digitorum longus caused si gnificant decreases in contact area, pressure, and force beneath the t oes and significant increases in contact area and force under the fore foot, Bending moments in the second metatarsal were shown to vary dire ctly with peak pressure under the second metatarsal head (r = 0.801). These findings demonstrate the load distributing function of the extri nsic plantar flexors during heel rise.