The contributions of the plantar fascia to foot function during running

The windlass and the arch-spring are two fundamental models that describe foot function during locomotion. However, the windlass mechanism requires that the plantar fascia is stiff and doesn’t strain, while the arch-spring describes a straining tissue. To examine how these two mechanisms function during barefoot overground running, we used biplanar videoradiography to measure the motion of the individual foot bones and drive a model of plantar fascia elongation. Our results show that distinct phases of each mechanism occur for every subject but vary in length and interaction time. The windlass may act to orient the foot into an optimal position so as to preferentially load certain structures of the foot while protecting others.