The reliability of a rambling-trembling analysis of center of pressure measures.

The center of pressure (COP) measures are most commonly used in postural studies (e.g., COP range, sway path length and mean COP velocity). Relatively new method based on the equilibrium point hypothesis that addresses more explicitly the dynamic nature of COP and represents more subtle aspects of postural control is the rambling (RM) and trembling (TR) decomposition of a stabilogram. With this method, the COP trajectory can be decomposed into deviations resulting from supraspinal (i.e., RM) and spinal processes (i.e., TR). The trajectory generated by shifting COP is referred to as RM and its difference from the original COP signal is referred to as TR. Although there is still scientific discussion as to whether this method gives valuable additional information about postural control processes, it is gaining popularity. Unfortunately, there is lack of standardization in the methodology of data collection for this approach, particularly with respect to the number of trial repetitions and their duration. The objective of this study was to assess the reliability of RM-TR measurements. Fifteen young, healthy male subjects performed ten 120-s trials of quiet standing. Measurements of RM, TR and COP were calculated using the first 30, 60, 90 and 120-s of each trial. An ANOVA-based ICC model was used to estimate the reliability. The results of this study suggest that at least three 60-s trials should be used when using selected measures of RM-TR.