Coordination patterns of foot dynamics in the control of upright standing.

In this study, two force platforms were synchronized to investigate the coordination of the right and left foot center of pressure (COP(R) and COP(L)) and its relation to the COP(NET) in the control of 5 upright postures with and without visual information. The results revealed that the standard deviation (SD) of COP(L), COP(R), and COP(NET) progressively increased in the more challenging staggered and tandem stances, respectively, and to a lesser degree with the absence of visual information. Circular analysis of the relative phase of COP(L) and COP(R) revealed that the coupling pattern and variability were dependent on postural stances and the availability of vision. A negative correlation between the variability of the relative phase of the two feet COPs and the SD of the COP(NET) in the anterior-posterior (AP) direction was evident most strongly in the no vision conditions. Thus, the asymmetry of the mechanical constraints on the feet as a function of stance organize the coordination patterns of the feet COPs while the degree of adaptive variation between the feet COPs is dependent on both the mechanical constraints and the availability of vision.