Dynamical structure of center of pressure fluctuations in elderly people.

This study investigates whether aging has an influence on the dynamics of the fluctuations of the displacement of the center of pressure (COP), during quiet standing. Two groups of healthy subjects were compared (11 young and 12 elderly) for two visual feedback conditions (eyes open and eyes closed). The data were analyzed using (i) classical stabilometric variables (length and surface) and (ii) recurrence quantification analysis (percentage of determinism and entropy), for the dynamical structure of COP signals. The length of the COP displacement was found to be the best discriminating stabilometric variable for both visual and aging effects. Visual feedback influenced recurrence quantification analysis (RQA) variables only for the elderly group. Both RQA outputs in the anterior posterior direction were sufficient to distinguish the young and elderly groups. The entropy estimation computed by RQA was significantly reduced for postural fluctuations in elderly people. We conclude that classical stabilometric variables and RQA outputs provide complementary information for the characterization of ageing effects on postural sway.