How Are Statistical Parameters of the Velocity Vector of Body Sway Distributed in Normal Human Subjects?

The velocity vector when the human body sways has been qualitatively evaluated in clinical sessions. We quantitatively measured the velocity vector for 1 min in 89 normal subjects standing in a stable posture, and examined distributions of quantities of the velocity vector. The velocity vector was measured with a stabilometer, which visualizes the vector as magnitudes radially projected from the center to the periphery into 36 directions by 10°. The 3 quantities we calculated from the 36 scalars of the vector per subject were the coefficient of correlation (CV), skewness and kurtosis, which were analyzed statistically. Values of skewness were normally distributed. Values of CV and kurtosis were log-normally distributed when adjusted with log transformation. Then, we calculated standardized values of the normal distributions, from which the lower and upper cutoff values in the 95% and 99% areas were available. The 3 quantities showed statistically significant correlations with one another, although the levels were low. Thus, in the present study, use of the 3 parameters enabled us to quantitatively evaluate the whole image of velocity vector, which would simplify the procedures of examination and shorten the time required for differential diagnosis.