Intrasession reliability of the “center of pressure minus center of mass” variable of postural control in the healthy elderly

Corriveau H, Hébert R, Prince F, Raîche M. Intrasession reliability of the “center of pressure minus center of mass” variable of postural control in the healthy elderly. Arch Phys Med Rehabil 2000;81:45-8. Objectives: To estimate the intrasession reliability of a single measure of the biomechanical variable “center of pressure minus center of mass” (COP-COM) to determine, first, how many trials must be averaged to obtain a reliable measure of postural stability, and second, the minimal metrically detectable change of the COP-COM. Participants: Community-living, healthy, elderly people over 60 years of age (n = 7). Design: Measurements were made in double leg stance, eyes-open condition. Nine successive trials, with rests between, were carried out for each subject. Data Analysis: Intraclass correlation coefficients (ICCs). Main Outcome Measure: The biomechanical variable COP-COM, which represents the distance between the center of pressure and the center of mass, was measured from two force platforms and three position sensors. Results: The ICCs obtained for one measure of the COP-COM were .79 in the anterior-posterior (AP) direction and .69 in mediolateral (ML) direction. With four trials, the COP-COM variable is reliable at .94 in the AP direction and .90 in the ML direction. Minimal metrically detectable changes were .10mm (AP) and .16mm (ML). Conclusion: Using four repetitions of the COP-COM variable provides a reliable measurement of postural stability. © 2000 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation