Fractal properties of postural sway during quiet stance with changed visual and proprioceptive inputs.

We studied the fractal dynamics of postural sway during quiet stance with changed visual and/or proprioceptive information. Radius-vector length and angle of rotation of center of foot pressure (COP) displacements were used as parameters of postural sway. The experiments were performed on 24 healthy volunteers of both sexes aged 20-30 years. Using a battery of nonlinearity tests, differences in the degree of fractality of both parameters during stance were found. We found that the behavior of radius-vector was similar to fractional Brownian motion, while that of angle of rotation was similar to flicker noise. Quantitative parameters that can be used to characterize the changes in radius-vector length and angle of rotation include self-similarity intervals and fractal dimension. In healthy subjects, the process of postural control maintains its fractal structure independently of altered sensory information. We believe that this analysis provides information about new methods for evaluating postural sway behavior during quiet stance.