Computer Simulation of the Effects of Muscle Co-activation and Joint Stiffness on Postural Stability

Abstract

Postural stability is affected by several biomechanical factors including posture, foot placement, intrinsic muscle stiffness, and joint stiffness due to muscle co-activation. Increasing natural postural stability could make balance control easier for individuals with diminished postural responses. However, it is not clear which biomechanical factors most significantly contribute to the natural postural stability. The objective of this thesis is to simulate the effect of intrinsic muscle stiffness and muscle co-activation on the postural stability using a musculoskeletal computer model subjected to support-platform perturbations. We developed a customized static-optimization method to encourage co-activation using joint stiffness as an intermediate variable to improve postural stability. To this end, we also implemented a short-range stiffness muscle model and compared its stabilizing effects to a standard Hill-type muscle model. Our result showed that co-activation of muscles resulted in higher joint stiffness and higher postural stability and that intrinsic muscle short-range stiffness contributed significantly to postural stability.