Modeling and control of anterior-posterior and medial-lateral sways in standing posture

To study essential anterior-posterior and medial-lateral sways of the stance caused by rotational movements about the ankle and hip joints, a mathematical model is developed for the 3D postural kinematics and dynamics. The model is in the form of nonlinear differential-algebraic equations corresponding to a biomechanical system with holonomic constraints. A nonlinear feedback control law is further derived for stabilizing the upright stance, whilst eliminating internal torques induced by the constraints on postural movements. Numerical simulations of the model parametrized with experimental data of human body segments illustrate the performance of postural balancing with the proposed control.