The Reliability of Center of Pressure Sway Variables and Their Interrelationships in Healthy Individuals

This study examined the reliability of center of pressure (COP) sway variables and their interrelationships in healthy individuals. The subjects were 420 males and females with ages ranging from 10 to 87 yr. The COP sway for 1 min was measured three times. As the COP sway variables, 7 on general sway (GS) and 15 on the power spectrum (PS) were selected. In both sexes, the intraclass correlation coefficient (ICC) of GS variables was high (> 0.60), and that of the area ratio 1 of X, Y, and R directions and area ratio 3 of X direction in PS variables was also high (> 0.60). In both sexes, correlations between the GS variables except for the average position were over a moderate degree. For the PS variables, correlations between peak power values, between the parts of area ratio 1 (split ratio of power spectrum density [low (1), middle (2), and high bands (3)]), between the parts of area ratio 2, between area ratio 3’s Y and R (synthetic coordinate of X and Y) directions, and between area ratio 3’s X and R directions were over a moderate degree, but those between the other variables were either insignificant or below medium level even if significant. In both sexes, both areas and both standard deviations had correlations over a moderate degree with peak power values in the X, Y, and R directions. The GS variables and area ratio 1 of 3 directions and area ratio 3 of X direction of PS variables have relatively high reliability. Relatively strong relationships were found between the GS variables except for the average position and in the PS variables, those between peak power values and between area ratios 1 and 3 of Y and R directions, and between area ratio 3’s X and R directions are relatively high. Area and standard deviation variables of GS variables have a relatively high relationship to peak power values of three directions of PS variables. The reliability and interrelationships of COP sway variables show few differences concerning sex.