Standing balance strategy for horizontal sway of the support surface at constant frequencies

Abstract

Standing balance analysis to constant frequency sway of the support surface is expected to be effective for assessing the ability to balance in a particular situation. There are two control strategies for swaying below 0.7 Hz, one suppressing the head acceleration (mode 1) and the other suppressing the relative displacement of the center of mass (mode 2). However, the details of these control strategies remain unclear. The purpose of this study was to investigate control strategies when standing on a constant-frequency support surface, and to detect which of the two control strategies occurred. Thirty healthy subjects cooperated to measure the response to constant-frequency sways of 0.25 Hz and 0.50 Hz. Considering the control target, energy consumption, and energy equilibrium, we assumed a set of evaluation functions representing the control strategies describing the two modes, and derived unknown parameters to fit the experimental results. Consequently, the theoretical values of the two control strategies are obtained, and the mode can be detected by comparison with the theoretical values. Our findings may contribute to rehabilitation and evaluation using constant frequency sway.