Nonlinear Dynamics Analysis of Standing Stability in an Ankle–Knee–Hip Model

Abstract

Abstract. Falls among middle-aged and elderly individuals represent a major health concern. Understanding the mechanisms of human balance is crucial for risk reduction. To address this need, an ankle–knee–hip model, incorporating neuromuscular feedback delays and additional biomechanical parameters, was developed to capture the body's dynamic responses during ground‐level balance maintenance. Bifurcation analysis of the human model using the dde-biftool software identifies stability regions within several parameter spaces. This method allows for a rapid determination of system stability conditions based on the dynamical equations. Subsequently, numerical analysis is utilized to determine the motion state of the system under specific parameter conditions, which not only verifies the accuracy of the earlier stability assessment but also provides insights into the system's motion behavior by analyzing its specific behavior. The results not only advance the mechanistic understanding of human postural control under effects of delay and neuromuscular feedback gain but also provide quantitative guidelines for designing assistive devices and rehabilitation protocols aimed at fall prevention.