Objectives: 

Postural sway can be reduced when real-time visual biofeedback (VBF) of centre of pressure (CoP) position is provided. Reduction also occurs, when VBF is magnified. Purpose of this study was to determine optimal magnification of CoP position displayed on monitor.

Materials: 

In study participated 20 healthy young adults (9 M, mean age 26,5 yrs). Body sway was recorded by force plate, during quite stance in 10 conditions: stance on firm/foam surface with/without VBF presented at 4 magnifications (gains 1, 2, 5, 10). We evaluated 6 parameters of CoP: amplitude and velocity in anteroposterior (Ay, Vy) and mediolateral (Ax, Vx) directions, root mean square (RMS) and line integral (LI).

Results: 

Providing of VBF reduced postural sway during stance on both types of support surface. ANOVA revealed significant effect of gain in Ax, Ay and RMS. Significant effect of surface was found in all parameters. Significant interaction between surface and gain was observed in all parameters except Vy. Pairwise comparisons performed on each type of surface showed decrease of Ax, Ay and RMS during all VBF conditions except Ax on firm surface. Decrease of these parameters was also observed in VBF situations with greater magnifications comparing to lower.

Conclusions: 

Our results suggest that any magnification in range 1x-10x provides meaningful additional information for stabilization of posture. Greater magnification led to greater reduction of sway amplitudes and RMS. These parameters seem to be the most appropriate for testing the effectiveness of VBF. Standing on foam led to a greater decrease of these parameters. This suggests a marked reliance on vision to maintain balance in situation when the proprioceptive information from feet is altered. Velocity and LI of CoP did not show any increase which would suggest the voluntary activation in postural control. It is possible that other type of strategy (f.e. arousal of attention) is involved in the process of postural stabilization.