Study of Vertical Posture of Humans Standing with Different Orientations of One or Both Feet

Vertical posture of a standing subject with different orientations of one or both feet was studied. Symmetrical turn of both feet in a standing person led to an increase in the movement of the common center of pressure (CCP) and center of pressure (CP) of each foot. It is likely that, for the vertical position maintenance with symmetrical feet turn, the movement of the CPs of both feet was controlled simultaneously. During standing with the turn of one foot, the CP movement increased for the foot that retained orientation in the sagittal direction. For the turned foot the CP movement did not change. Thus, the turn of the foot of one leg changed the involvement of this leg in the upright position maintenance. The vertical posture was maintained mainly due to the position control of CP of the foot oriented in the sagittal direction. In addition, there was a change in the predominant direction of the CP movement relative to the foot orientation. When the foot was oriented in the sagittal direction, the predominant movement direction of the CP was turned outward. With the foot rotated outward, the predominant movement direction of the CP was turned inward. This change in the CP movement direction was observed in the cases of simultaneous turn of both feet as well as the turn of one foot. It can be assumed that, in standing, the balance-maintaining system controls the CP position of each leg and takes into account the torsional torque in the leg that occurs when the foot is rotated.