Test-retest reliability and minimal detectable change for center of pressure measures of postural stability in elderly subjects

Background: Postural instability has been identified as a potential precursor of falls in elderly subjects. Postural stability in quiet stance is commonly assessed with center of pressure (COP) measures. The purpose of this study was to determine testretest reliability and minimal detectable change (MDC) for the center of pressure (COP) measures in the elderly subjects. Methods: Eighteen healthy elderly people over the age of 60 years participated in this study. For each subject the COP was recorded during quiet upright stance on different levels of postural difficulty (eyes open versus eyes closed, firm surface versus foam surface) and lean condition (forward and backward). All measurements were done on two sessions with 7 days interval. These indices: mean velocity, standard deviation of amplitude, standard deviation of velocity, phase plane parameter and area (95% confidence ellipse). Intraclass correlation coefficient (ICC), standard error of measurement (SEM) and coefficient of variation (CV) were used to quantify testretest reliability. The MDC for each measure was calculated to quantify intervention effects. Results: In general, test-retest reliability of COP measures in the elder subjects was increased whenever postural difficulty of task increased in quiet standing. In standing conditions, mean velocity and phase plane parameter were the most sensitive and the most reliable measures. The lean range was the most sensitive and the most reliable measure, in the lean conditions. Conclusion: Center of pressure measures in the quiet standing especially in difficult postural conditions demonstrated high sensitivity in the older subjects. These results may be useful in quantification and assessment of balance performance and treatment efficacy.