Influence of the structure of the support surface under the sole on vertical posture during standing with different body weight distributions between legs

Abstract

The vertical posture was studied during standing with fееt on the support surfaces of different structures. The movements of the center of pressure (CP) of each leg and the common CP (CCP) were recorded while the subject stood with a support on a smooth floor and with the support of one foot on a spike mat (SM) with different load distributions between the legs. When the body weight was transferred to one leg during standing under ordinary conditions on a smooth floor, the CP of the loaded leg moved more than the CP of the unloaded leg; i.e., the posture sway was compensated mainly due to the activity of the loaded leg, which created a larger torque. When the subject stood with one foot on the SM, the CP movement of this leg did not depend on the leg load and was about 60% of the CP movement of the leg on the smooth floor. Apparently, the CP displacement of the unloaded leg on smooth support was larger than the CP displacement of the loaded leg creating the torque necessary for compensating the body sway. Thus, maintaining the vertical posture was carried out mainly by the leg standing on the smooth support. It is assumed that additional stimulation of different surface and deep receptors of the foot caused by foot support on the SM hampered the perception of its CP position, and the vertical posture was maintained mainly by the leg afferent signals from which more precisely reflected the CP position.