Reliability of force-platform measures of postural sway and expertise-related differences.

CONTEXT Although reliability is a population-specific property, few studies have investigated the measurement error associated with force-platform parameters in athletic populations. OBJECTIVE To investigate the skill-related differences between athletes and nonathletes in reliability of center-of-pressure (COP) summary measures under eyes-open (EO) and eyes-closed (EC) conditions. DESIGN Test-retest reliability study. SETTING COP was recorded during double-leg quiet standing on a Kistler force platform before and after a fatiguing treadmill exercise, with EO and EC. PARTICIPANTS 31 male participants including 15 athletes practiced in karate and 16 nonathletes. MAIN OUTCOME MEASURES Standard deviation (SD) of amplitude, phase-plane portrait, SD of velocity, mean total velocity, and area were calculated from 30-s COP data. Intraclass correlation coefficient (ICC), standard error of measurement, and coefficient of variation (CV) were used as estimates of reliability and precision. RESULTS Higher ICCs were found for COP measures in the athlete (compared with the nonathlete) group, postfatigued (compared with prefatigued) condition, and EC (compared with EO) tests. CVs smaller than 15% were obtained for most of the COP measures. SD of velocity in the anteroposterior direction showed the highest reliability in most conditions. CONCLUSIONS Tests with EC and to a lesser extent tests performed in the athlete group and in the postfatigued condition showed better reliability.