Verification of the adaptive parameters of the relative positions of the leading leg and the whole body at foot contact during split-belt treadmill walking

The main purpose of this study was to demonstrate that adaptive walking re-establishes dynamic stability at the time of foot contact in split-belt treadmill walking. First, we examined whether the relative positions of the center of mass (COM) and the center of pressure (COP) were re-established at foot contact during walking adaptation. We found that the symmetry of the COM-COP angles was re-established more completely than any other parameters (foot and pelvis markers) on both the fast and slow belt sides during the adaptation phase. Moreover, we examined whether the dynamic relationship between the COM and the COP was the same during tied- and split-belt walking. Our results showed that the equations related to the trailing leg relative to the COM re-converged around 0 at foot contact on both the fast and slow sides during the adaptation phase. We also showed that the COM-COP angle at foot contact is an adaptive parameter and is consistent between the fast and slow belt sides. At foot contact, the relative positions between the leading leg and the whole body can also be seen to be adjusted during trial-and-error adaptation to split-belt perturbation in which the belts move at different speeds. Therefore, we suggest that the relative positions of the COM and the COP at foot contact is the spatial reference for the gait cycle contribution to dynamic stabilization during adaptive walking.