Age-related changes in joint coordination during balance recovery.

Falls represent a significant health risk in the elderly and often result in injuries that require medical attention. Reduced ability to control motion of the whole-body center of mass (COM) has been shown to identify elderly people at risk of falling. To explore effective preventive strategies and interventions, we studied adult age-related differences in multijoint coordination to control the COM during balance recovery. We used the uncontrolled manifold (UCM) analysis, which can decompose movement variability of joints into good movement variability (motor equivalent) and bad movement variability (nonmotor equivalent). The good variability does not affect the COM position, while the bad variability does. Twenty-nine subjects, including 16 healthy young (26.1 ± 4.5 year) and 13 older (74.6 ± 5.6 year) adults without systematic disease, neurological disease, or a severe degenerative condition stood on a flat platform, and received an unexpected backward translation. The older adults had similar amounts of joint movement as the young adults during balance recovery except for the thoracic-lumbar joint. However, the UCM analysis showed that the older adults changed their joint coordination pattern to control the COM and had a lower motor equivalent index with increased nonmotor equivalent variability (bad variability). We conclude that normal aging adults lose the compensatory strategy of flexibly controlling multiple joints when stabilizing the COM after receiving a balance perturbation.