Postural Sway during Body Turn in Symmetrical and Asymmetrical Standing in Humans

Abstract

We studied the vertical posture in subjects in the standing position with different turns of the body and different distributions of the load between the legs. We recorded the motion of the projection of the common center of pressure (CCP) and of the center of pressure (CP) for the left and right legs. The predominant direction of CP movement was determined from a stabilogram, and then changes of this direction were analyzed during body turns and with different load distributions between the legs. Body turn led to the shift of the predominant direction of CCP movement towards the turn side. This change in the direction of CCP movement was observed with any load distribution between the legs. At the same time, weight transfer to one leg also led to the direction shift of CCP movement towards the loaded leg. The direction of CP movement of the loaded leg did not change, but the direction of CP movement of the unloaded leg shifted clockwise upon unloading both right and left legs. We assume that the changes in the mechanisms of maintaining the vertical position with asymmetric distribution of the leg load may be associated not only with the change in the force interaction with the supporting surface, but also with asymmetry of axial muscle tone.