Oscillations of upper and lower body segments in the sagittal plane during standing: Spatiotemporal relationships

Abstract

The balance control in the sagittal plane during standing without visual feedback has been studied in the context of the notion that a human body can be presented as a two-segment inverted pendulum. The oscillations of the center of pressure and of upper and lower segments were recorded for 2 min (ten records, seven volunteers). It was shown that the correlation coefficients and dynamical similarity between the oscillation of the upper segment and the center of pressure are significantly higher than between the lower segment and the center of pressure. The dynamic similarity between the oscillations of the upper segment in different records are higher than between the oscillations of the lower one, which supposedly is connected with the necessity of the stabilization of the head in space during standing. The oscillations of the lower segment occurred with a delay of 16.2 +/- 9.0 ms relative to the oscillations of the upper segment. At the same time, the distribution of the delays has maximum at zero (it is asymmetrical), indicating that two strategies of balance control are used during quiet standing, which are described by a one-segment and a two-segment model of inverted pendulum.