Assessment of the effects of sensory perturbations using fourier-bessel expansion method for postural stability analysis

Center of pressure (COP) measurements are often used to identify balance problems. A new method for COP signal analysis using mean frequency is proposed in this paper. The computation of mean frequency is based on the Fourier-Bessel (FB) expansion that is suitable for use in non-stationary COP signals. In addition, FB expansion provides better frequency resolution and low frequency detectability. Seventeen subjects were tested under eyes open and eyes closed conditions, with different vibration frequencies applied for the eyes closed condition in order to further perturb sensory information. More accurate estimates of mean frequency were obtained for 200-point segments, with significant increase in mean frequency observed over time as subjects recovered from the initial perturbation of stepping on to the force plate. Subjects were significantly more stable in the mediolateral direction compared to anteroposterior one. Mean frequency as calculated by FB expansion was able to distinguish between eyes open and eyes closed conditions .p < 0:05/, but no effect of vibration could be detected.