A two-part, viscoelastic foot model for use in gait simulations.

A three-dimensional, two-part model of the foot, for use in a simulation of human gait, is presented. Previous simulations of gait have not included the foot segment (e.g. Siegler et al., 1982, J. Biomechanics 15, 415-425) or have fastened it to the ground (e.g. Onyshko and Winter, 1980, J. Biomechanics 13, 361-368). A foot model based on viscoelastic elements (e.g. Meglan, 1991, Ph.D. thesis, Ohio State Univ.), allows more freedom of movement and thus models the physical system more closely. The current model was developed by running simulations of the foot in isolation from just before heel contact to just after toe-off. The driving inputs to the simulation were the resultant ankle joint forces and moments taken from a gait analysis. Nine linear, vertically oriented spring/damper systems, positioned along the midline of the foot were used to model the combined viscoelastic behaviour of the foot, shoe and floor. Associated with each vertical spring/damper system were two orthogonally placed, linear, horizontal dampers used to provide the shear components of the ground reaction force. Torques at the metatarsal-phalangeal joint were supplied by a linear, torsional spring and damper. Control about the vertical axis and the long axis of the foot was achieved by the use of linear, torsional dampers. The predicted kinetic and kinematic values are very similar to those taken from the gait analysis. The model represents an improvement over previous work because the transition from swing to stance was smooth and continuous without the foot being constrained to any specific trajectory.