A stiffness-varying model of human gait.

We report on a conceptual two degrees of freedom (2 DOF) human gait model, which incorporates nonlinear joint stiffness as a stabilizing agent. Specifically, muscle spring-like property provides inherent stability during gait movement using a nonlinear angular spring and dash pot at each joint. The instability problem of the gait model in direct dynamic analysis is overcome by simulating the human co-contraction muscle function. By developing dynamic system stability requirements and hypothesizing a minimum joint stiffness criterion, we determine time-varying joint stiffness. Optimum joint stiffnesses are present for varying gait pattern, stride lengths and cadences. We conclude that nonlinear joint stiffness can be incorporated into gait models to overcome stability problems inherent in such linkage models.