Examination of the factor structure of center of foot pressure movement and cross-validity.

This study aimed to determine the factor structure of the center of foot pressure (CFP) movement during static upright posture, and to objectively categorize and summarize parameters to evaluate CFP movement. The subjects were 220 healthy young males and females. The measurement of CFP was carried out 3 times with 1 min rest and the mean of trials 2 and 3 was used for the analysis. The measurement device was an Anima's stabilometer G5500. The data sampling frequency was 20 Hz. Thirty-four parameters with high reliability were selected from the following 6 domains except for the center position which is a fundamental attribute: distance, distribution of amplitude, area, velocity, power spectrum, and body sway vector. Factor analysis (principal factor method and promax rotation) was applied to a correlation matrix consisting of 32 parameters. Four factors abstracted were interpreted as follows; unit time sway, front and back sway, left and right sway and high frequency band of power spectrum. The reliability coefficient (ICC=0.89-0.95) and the congruence coefficient (phi=0.80-0.97) between factors abstracted from the original and the cross-validity groups were very high. It was considered that the CFP movement consists of the above 4 factors that evaluate the amount of body sway and can be synthetically evaluated by them.