Stance and sensory feedback influence on postural dynamics

This study examined the effects of ice-induced plantar desensitization and the withdrawal of visual feedback on the magnitude and time-dependent structure of postural sway variability. The magnitude of variability was quantified as the area of an ellipse enclosing 95% of the center of pressure (COP) time-series during normal and tandem stances. The same time-series were also analyzed using Approximate Entropy (ApEn) and Cross-Approximate Entropy (CrossApEn) as indices of irregularity and asynchrony between the mediolateral and anteroposterior COP motions. Variability increased during tandem stance and this increase was compounded by both visual feedback withdrawal and cutaneous desensitization. Both ApEn (mediolateral and anteroposterior COP motion) and CrossApEn increased with the withdrawal of visual feedback during the tandem stance, but decreased significantly during normal stance. The results of the study demonstrate that plantar desensitization only affected the magnitude of sway variability but did not alter its time-dependent structure. Contrasting effects on the structure of postural sway variability with visual feedback withdrawal were observed during the different stances, highlighting the role of task demands in postural dynamics.