A preliminary study on the effects of fixation of joint degrees of freedom on postural fluctuation

Abstract

The present study aimed to elucidate 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 considered a complex system. Postural fluctuation can be considered a representative of system dynamics and easily measured. Therefore, it is expected to be useful for assessment of fall risk in elderly people. Recently, clinical studies have not only applied linear methods but also nonlinear methods of assessment to evaluate static and dynamic balance abilities. In our presentation, we report the result of our preliminary 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 with no 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. As a result, static measure (COP trajectory length) did not significantly differ across the conditions. On the other hand, the dynamic measurement (the detrended fluctuation analysis scaling exponent) was significantly higher in the ankle-fixation condition in the mediolateral (ML) direction. These results suggest that although static balance ability was not affected, dynamic balance ability (anti-persistent behavior) was reduced under the ankle-fixation condition in the ML direction by constraining the DoF.