Age differences in the control of postural stability during reaching tasks.

Reaching tasks are commonly performed during daily activities and require anticipatory postural adjustments (APAs) to ensure a stable posture during movement execution. Age-related changes in APAs may impact dynamic balance and cause postural instability during reaching tasks made from standing. The present study examined age differences in postural control during reaching to targets located at different heights. Fourteen young adults (aged 20.0±1.5 yrs) and 16 community-dwelling older adults (aged 73.4±5.3 yrs) participated in the study. The task involved reaching forward to grasp a cylinder, and returning to an upright position as fast and accurately as possible. Postural control was analyzed using the center of pressure (COP) during four phases of the task: COP displacement during APA production, COP trajectory smoothness during the reach and return phases, and COP path length during the recovery phase following movement. APA amplitude measured by COP displacement and COP path length during the recovery phase was larger in older compared to young adults. Dynamic balance represented by COP trajectory smoothness was reduced with age. In both age groups, APA amplitude was largest and COP trajectory smoothness the least during low target reaches. The results demonstrate that, while older adults can alter APAs in order to maintain postural stability, control of COP during movement execution, particularly during low target reaches, is compromised with aging. These findings have clinical implications for both the assessment of dynamic balance and the development of balance training programs.