Phase synchronization of foot dynamics in quiet standing

This study was set-up to investigate the effect of mechanical constraints arising from different postural stances on the AP and ML pattern of the time evolutionary properties of phase synchronization of the foot dynamics, together with their relation to the dynamics of COP(NET). The results showed that postural stance differentially influenced the phase synchronization (number and duration of the epochs) between the individual feet COPs and of each foot to the COP(NET). The side-by-side stance had longer phase synchronization duration in the anterior-posterior (AP) direction and shorter duration in the medial-lateral (ML) direction than the staggered and tandem postures. In the staggered and tandem postures, the relative phase between the rear foot COP and the COP(NET) had longer phase synchronization than the relative phase between the COPs of the two feet and that between the front foot COP and the COP(NET). The time evolutionary properties of the feet coupling dynamics revealed patterns of "stable" but "flexible" control of the postural system as a function of the asymmetrical foot loading in the stance.