A method of determining in vivo dynamic human ankle stiffness during external foot rotation

Abstract

This study presents a method to determine stiffness of the human ankle in internal–external rotation, inversion–eversion, and plantarflexion–dorsiflexion during an in vivo, single-legged, external foot rotation experiment. Five young male subjects stood on one foot and performed an internal rotation of the body (external rotation of the foot) on a force plate, while motions were captured with a motion capture system. Hindfoot rotations relative to the tibia and resistive moments in the above three directions were obtained using a commercial software package. The resistive moments were plotted against rotation during the loading portions of the curves. Linear approximations of these curves were used to determine stiffness of the ankle in directions of internal–external, inversion–eversion, and plantarflexion–dorsiflexion. Future data from the above experiment and other athletic motions may be useful for the design of surrogate devices used to evaluate the potential performance and ankle injury risk characteristics of various shoe–surface interfaces.