Modeling the Fatigue-related Changes in the Ground Reaction Force and Soft Tissues Vibrations during Running

The effects of fatigue on the ground reaction force (GRF) and the vibrations of the human lower extremity soft tissues are studied in this paper. A recently developed multiple degreesof-freedom mass-spring-damper model of the human body during running is used for this purpose. The model is able to take the muscle activity into account by using a nonlinear controller that tunes the mechanical properties of the softtissue package (i.e. stiffness and damping) based on two physiological hypotheses, namely “constant-force” and “constant-vibration”. To model muscle fatigue, it is assumed that the range of variations of the mechanical properties of the lower body soft-tissue package reduces over time. Simulations are carried out for various shoe hardness parameters and various preand post-fatigue conditions. The simulation results show that the vibration amplitude of the lower body soft-tissue package increases with muscle fatigue. However, fatigue does not have any significant impact on the GRF.