The intra-session and inter-session reliability of centre-of-pressure based measures of postural sway within a normal population

Abstract

The objectives of this study were to (1) determine the intra- and inter-session reliability of centre-of-pressure (COP) based measures of postural stability of a normal population and (2) establish a standardised protocol easily repeatable at a tertiary teaching and research facility. Thirty-four subjects (19 females: mean age 25+/-4; 15 males: mean age 29+/-7; age range 19-42 years) were recruited for this study. COP trajectory was recorded using a Medicapteurs S-Plate during three sessions performed over four weeks (week one, two and four). Each trial was comprised of six 75-second tests, three with eyes open and three in eyes closed conditions. The following COP parameters were measured, Average Speed (medial/lateral & anterior/posterior), Length of COP path, Area of COP path and Root Mean Square area (RMSa). The relative and absolute intra- and inter-session reliability was assessed using intra-class correlation coefficient (ICC) and coefficient of variation (CV). Intra-session reliability proved superior to inter-session reliability in majority of the COP parameters studied, shown by consistently higher ICC values than their inter-session equivalents. Average Speed (medial/lateral & anterior/posterior) and Length of COP path were the most reliable parameters within and between sessions obtaining Large to Very Large correlation (0.7-0.9) independent of visual input. In addition this study investigates the relationship between subjective pain intensity and anthropometric characteristics and postural stability in this sample population. This study does not show any meaningful relationship between postural stability and pain, age, height, shoe size, body mass index. However, results suggest that females may have slightly poorer postural stability than males. The information gained through this study maybe a useful foundation for future research in postural stability and the factors that influence it.