Center of pressure based assessment of balance responses to repeated perturbations of upright stance

In this study a description of balance response to sudden external perturbations of the upright posture was performed. To this aim, subjects underwent to a series of translational perturbations at fixed speed in backward and forward direction. Center of pressure (CoP) displacement was analyzed in terms of temporal and spatial characteristics, showing a repeatable waveform which allowed the identification of two main response periods: the destabilizing and the counterbalancing phase. Different control features of balance response have been observed in both phases, with a temporal-based control of CoP displacement in the first phase and an amplitude-based control in the second one. Moreover, the analysis of CoP could be useful to identify the presence of the first trial effect and the habituation rate, two well-known features of perturbed posturography. These findings could contribute to the understanding of balance control in perturbed conditions and suggest CoP as a valuable measure in studying not only the quiet but also the perturbed stance.