Restricting the Center of Mass Motion Via Multisegment Versus Localized Constraints: Its Impact on the Center of Pressure Behavior

Artificially restricting the center of mass (COM) motion during quiet standing through multisegment constraints has previously been shown to alter center of pressure (COP) dynamics. Increases in COP motion during such mechanically restricted stances have been interpreted as potential markers of exploratory behavior, whereby the central nervous system may generate movements to gather sensory input that would otherwise be limited by the imposed constraints. However, past studies relied on a plank-based apparatus that places participants in a nonecological posture, potentially limiting interpretations. This study compared the effects of the plank-based setup and a more ecologically valid belt-based apparatus that restricts COM movement without fully constraining the body. The analysis focused on both traditional measures of COP (i.e., variability) and dynamic measures (i.e., regularity and frequency components). Participants performed standing trials with both apparatuses, with eyes open and closed. Results revealed distinct COP behaviors between the two systems: compared with the unrestricted condition, the restricted condition with the plank-based apparatus yielded higher COP variability and regularity, whereas the belt-based system yielded lower COP variability and increased irregularity. These effects were not strongly influenced by visual input. The persistent COP motion observed under both conditions suggests that COP displacement may serve functions beyond merely stabilizing the COM, possibly reflecting exploratory behaviors. Overall, our findings support the use of belt-based systems as a more ecological alternative for restricting the COM motion, allowing for the study of the role of the COP in sensorimotor regulation without the limitations of a multisegment constraint.