TEMPORAL AND FRACTAL BEHAVIOR OF THE CENTER OF PRESSURE IN PARKINSONIAN AND HEALTHY ELDERLY COHORTS DURING QUIET STANDING

Abstract

This study investigated the quantitative scaling properties of the center of pressure (COP) as well as the spatial-temporal properties of the COP to elucidate the postural control behavior of healthy elderly (HE) adults and adults with Parkinson’s disease (PD) during quiet standing. Eighteen adults with PD and eighteen HE adults participated in this study. The COP movements were recorded while participants stood on either a firm surface or on a foam pad with their eyes either opened or closed. The sway ranges in the anterior–posterior (AP) ([Formula: see text] and medio-lateral (ML) ([Formula: see text] directions, the total length of the trajectory ([Formula: see text], sway area ([Formula: see text], and scaling exponents ([Formula: see text] from detrended fluctuation analysis were computed from the measured COP data. All temporal variables of the COP in all conditions were found to be significantly larger in the PD group than in the HE group. Low scaling exponents obtained for the PD group showed this group possessed diminished postural control ability compared to the HE group. The PD group showed unpredictable open-loop control in both the AP and ML directions. This proprioceptive control became predictable and the time scale relations decreased as the postural challenges increased. The AP and ML closed-loop control of the PD group was more predictable than that of the HE group only when proprioception was distorted using intact visual input, and the visual and proprioceptive inputs were both intact.