Study of the relative timing of shear forces on the sole of the forefoot during walking.

A portable recording device for the measurement of ambulatory longitudinal shear forces in a horizontal plane under the forefoot is described. The timing of the shear forces under 40 feet has been investigated, together with the relationships to each other and to body weight, leg length, cadence, velocity and stride length: they are compared by regression analysis. Shear forces under the forefoot are shown to occur for approximately 73-80% of the stance time. The maximum longitudinal shear forces and the maximum vertical forces are shown to occur at the same time under the first, fourth and fifth metatarsal heads.