Use of motor abundance in old adults in the regulation of a narrow-based stance

Purpose T he ability to maintain stable balance while standing decreases with age. The body must coordinate multiple joints using "freeze" or "free" strategy, or a combination of both to ensure balance stability. The purpose of this study was to examine age-related changes in the use of motor abundance during upright stance on a narrow base without visual input. ;Methods Uncontrolled manifold (UCM) analysis was used to decompose the movement variability of joints into goal-equivalent variability (GEV) and non-goal-equivalent variability (NGEV). The ratio between GEV and NGEV (UCMratio) quantifies the joint coordination related to postural stability, and a high UCMratio value indicates flexible control of joints. To perform balance tests, participants in this study (healthy young and old adults, 20 each) were asked to stand on a flat platform and on narrow wooden blocks with their eyes open and then eyes closed. ;Results In upright balance tests, both old and young adults maintained postural stability. GEV was greater than NGEV across all participants and conditions. However, GEV was higher in the young adults than in the old adults, whereas NGEV was higher in the old adults than in the young adults. Therefore, the old adults exhibited a lower UCMratio than the young adults. ;Conclusion T he old adults were unable to exploit motor abundance and used a less flexible multi-joint coordination pattern to achieve stable balance. The UCMratio value reflects the quality of postural control and can be used for assessing joint coordination in balance disorders