Postural Control During Standing

Mechanics of Standing

While standing, angular motion of the body is controlled by the torque about the CM produced by the force of the ground on the feet (foot force). That torque depends on the magnitude, location (center-of-pressure CP), and direction of the foot force. The foot force varies only slightly off vertical and the vertical acceleration is negligible so that the magnitude of the foot force remains nearly constant. Thus, the two primary factors driving angular motion are the CP and direction of the foot force. Historical and contemporary analyses of standing report only the CP and not the force direction and have thus been incapable of adequately considering precisely how humans maintain upright posture while standing.

Kinetic Approach

We have designed and built a custom force plate with enhanced capacity to measure the small changes in CP and force direction present during quiet standing. Initial sagittal-plane analysis of our measurements shows that shifts in CP with respect to the CM have two frequency components with behaviors that resemble the behaviors we previously observed in walking and seated pushes.


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