The coordinated regulation of posture during quiet standing

This paper proposes the hypothesis that postural regulation by a quietly standing human can be modeled as the solution to an optimal control problem. The performance measure being minimized is the sum of a quadratic term in the controls and either the center of pressure or the horizontal projection of the center of gravity raised to the fourth power. To test this hypothesis the human body is modeled by a system of three rigid links, jointed at the ankle and hip, moving only in the sagittal plane. We have solved the resulting constrained nonlinear optimal control problem by means of the same method used in Model Predictive Control. Simulations of the optimal control demonstrate qualitative agreement to the joint angle trajectories observed experimentally.