Relationship Between Oscillations About the Vertical Axis and Center of Pressure Displacements in Single and Double Leg Upright Stance

Abstract

The purposes of this study are to assess the relationship of the center of pressure (CoP) displacement parameters along the mediolateral and anteroposterior axes to whole-body oscillations about the vertical axis during single or double leg upright stance and to determine whether sensory deprivation and stance modify balance stability about the vertical axis and in the horizontal plane. Eleven male adults stood on a force plate during conditions in which stance (single/double) and/or vision (normal/reduced) were modified independently. The dependent variables were CoP range, CoP velocity, and free moment (TZ) range. R-squared coefficients (R) were applied to assess the relationship between CoP and TZ range, whereas multifactor analysis of variances were used to assess the differences among conditions. R between CoP and TZ parameters varied from 0.16 to 0.69 for three of the four conditions, suggesting that different postural mechanisms controlled CoP displacements and body axial rotations. Single leg stance with reduced vision condition revealed a higher R between CoP velocity and TZ range. TZ range was approximately seven times greater when stance was modified to single limb stance, whereas reduced vision had no effect. Postural control mechanisms seem to be different for the free moment (TZ) than for the CoP displacements.