Role of the visual feedback on balance responses to upright stance perturbations

In this study an evaluation of visual feedback on the balance response to upright stance perturbations is proposed. Subjects underwent to base of support translations in backward direction at fixed velocity in an eye-open (EO) and eye-closed (EC) condition. Center of pressure (COP) and center of mass (COM) were acquired, showing a repeatable double-peak shape which mirrors two different response periods: a destabilizing phase and a counterbalancing phase. Thus, COP and COM were analyzed on the basis of their temporal and spatial features. Further, also the angular displacement of lower limb joints, trunk and head were considered and lower limb muscular activity in terms of myoelectric latencies. Results showed several differences in COP and COM based parameters between EO and EC condition. Moreover, angular range variations seemed to indicate a different role of each joint in the two considered sensory conditions, highlighting the switch from an ankle-based strategy (EO condition) to a more complex kinematic strategy (EC condition). Outcomes of this study could add information about: (A) the suitability of considering COP displacement in perturbed posture analyses with sensory deprivation and (B) the significant role of the visual feedback in balance maintenance when a sudden and quasi-impulsive disruption is employed.