Inter- and intrafoot coordination when standing on balance boards.

The experiment was set up to investigate the inter- and intrafoot coordination dynamics of postural control on balance boards. A frequency domain principal component analysis (PCA) was applied on 4 center of pressure (COP) time series collected from two force platforms to reveal their contributions to postural stability. The orientation of support played a more significant role than its width in channeling the foot coordination dynamics. When the support was oriented along the AP-challenging direction, the 4 COPs revealed a parallel contribution to the 1st principal component (PC1) indicating an interdependence of the foot coordination in both directions. When the support was positioned along the ML-challenging direction, the COPs in the AP direction showed larger weightings to PC1 implying an interfoot coordination. These findings provide evidence that COP coordination operates in adaptive ways to sustain postural stability in light of changing support constraints to standing.