Relationship between body factors and postural sway during natural standing

The aim of this study was to investigate the associations of body factors (anthropometry and foot placement) with postural sway during natural standing and their possible sex differences. Forty young subjects (20 men and 20 women) performed quiet natural standing on a force platform in self-selected feet distance. Five body factors (height, weight, body fat ratio, feet-opening angle, feet distance) were selected as cardinal independent variables from the colinearity analysis. Outcome measures were derived from the center of pressure and included spatiotemporal sway size variables and upper limit frequency of main (95%) power component of sway. Significant sex differences were observed in the correlation of outcome measures with body factors. In women, postural sway size (mean distance and mean velocity) increased with height and weight. In contrast, men showed insignificant change in sway size but significant reduction in sway frequency with height and weight. Stepwise multiple regressions were conducted to investigate the determinants of outcome measures. In case of sway size measures, physique (height and weight) was the major determinant in women but not in men. In case of sway frequency, physique and feet opening angle were the major determinants in men but not in women. Postural control strategy related to body factors is apparently different between sexes, and therefore, extreme care must be taken in normalization of postural sway variables.