The role of task constraints in relating laboratory and clinical measures of balance.

This study tested the hypothesis that age-related postural control deficits are more clearly detected from force plate recordings when using postural control tasks with an explicitly defined goal as opposed to the frequently used quiet stance task. Eighteen older adults (over 65) and seventeen younger adults (under 30) stood on a force plate with visual feedback (VFB) of the center of pressure (COP) and without such visual feedback with eyes open (NVFB). In the VFB condition, online visual feedback about the COP was provided and participants maintained that feedback on a stationary visual target for 80s. We hypothesized that age-related difference in COP variability (standard deviation of COP position and average absolute maximum COP velocity; AAMV) would be more pronounced in the VFB than in the NVFB condition. In addition, we hypothesized that Berg balance scale (BBS) scores for older adults would correlate more strongly with the COP measures in the VFB condition than in the NVFB condition. Results showed that VFB enhanced age-related differences only for AAMV in anterior-posterior direction. Both age groups decreased postural sway when using VFB. Older adults increased AAMV with VFB while young adults did not, indicating that the task modified their postural control strategy stronger than in younger adults. BBS scores were correlated with the AAMV in both feedback conditions, while COP position variability was more clearly correlated with BBS in the VFB condition. These results suggest that the quiet stance task is sufficient to index balance function if velocity-based COP variables are utilized in the analysis.