Dynamic function of medial foot arch.

The purpose of this study was to analyse the dynamic function of the medical arch in the foot during walking. The change of the medical arch was measured by an "electro arch gauge" (EAG). The change of the medical arch, the angle of first metatarsophalangeal joint, ground reaction force and action potential of the tibialis anterior muscle, peroneus longus muscle, triceps surae muscle, abductor hallucis muscle, and the flexor hallucis muscle were measured simultaneously. In customary gait, the medical arch was stretched rapidly just after heel-strike and become longest at the early period of the foot-flat phase, then shortened gradually until about heel off. After that it was stretched slightly and shortened rapidly just before toe-off. Dynamic change of the medial arch occurred under a complex relationship of body weight, bone structure, ligaments and muscular force.