Effects of fixation of joint degrees of freedom on the complexity of postural dynamics

Abstract

The present study aimed at examining the direct relationship between the degrees of freedom (DoF) of embodied systems and postural fluctuation. An embodied system consists of various DoF and can be a complex system. Postural fluctuation can be easily measured and considered as a representative of system dynamics. Therefore, it is expected to be useful for a fall risk assessment among elderly people. Recently, clinical studies have applied both linear and nonlinear methods of assessment to evaluate static and dynamic balance abilities. In our presentation, we report on the result of our experiment that examined the effect of joint DoF fixation on postural dynamics. Young healthy male participants were asked to maintain their balance during a single leg standing task without fixation or with ankle/knee joint fixation. The time series data of the center of pressure (COP) were collected and analyzed using linear and nonlinear methods. The static index (COP trajectory length) did not significantly differ across the conditions. However, the dynamic index (sample entropy) was significantly lower under the ankle-fixation condition in the mediolateral (ML) direction. These results suggest that although the static balance ability was not affected, dynamic balance ability, in terms of complexity, was reduced under the ankle-fixation condition in the ML direction by constraining the DoF.