Adaptation effects in static postural control by providing simultaneous visual feedback of center of pressure and center of gravity

BACKGROUND: The benefit of visual feedback of the center of pressure (COP) on quiet standing is still debatable. This study aimed to investigate the adaptation effects of visual feedback training using both the COP and center of gravity (COG) during quiet standing. METHODS: Thirty-four healthy young adults were divided into three groups randomly (COP + COG, COP, and control groups). A force plate was used to calculate the coordinates of the COP in the anteroposterior (COP(AP)) and mediolateral (COP(ML)) directions. A motion analysis system was used to calculate the coordinates of the center of mass (COM) in both directions (COM(AP) and COM(ML)). The coordinates of the COG in the AP direction (COG(AP)) were obtained from the force plate signals. Augmented visual feedback was presented on a screen in the form of fluctuation circles in the vertical direction that moved upward as the COP(AP) and/or COG(AP) moved forward and vice versa. The COP + COG group received the real-time COP(AP) and COG(AP) feedback simultaneously, whereas the COP group received the real-time COP(AP) feedback only. The control group received no visual feedback. In the training session, the COP + COG group was required to maintain an even distance between the COP(AP) and COG(AP) and reduce the COG(AP) fluctuation, whereas the COP group was required to reduce the COP(AP) fluctuation while standing on a foam pad. In test sessions, participants were instructed to keep their standing posture as quiet as possible on the foam pad before (pre-session) and after (post-session) the training sessions. RESULTS: In the post-session, the velocity and root mean square of COM(AP) in the COP + COG group were lower than those in the control group. In addition, the absolute value of the sum of the COP − COM distances in the COP + COG group was lower than that in the COP group. Furthermore, positive correlations were found between the COM(AP) velocity and COP − COM parameters. CONCLUSIONS: The results suggest that the novel visual feedback training that incorporates the COP(AP)–COG(AP) interaction reduces postural sway better than the training using the COP(AP) alone during quiet standing. That is, even COP(AP) fluctuation around the COG(AP) would be effective in reducing the COM(AP) velocity.