The effect of age, movement direction, and target size on the maximum speed of targeted COP movements in healthy women.

Rapid center of pressure (COP) movements are often required to avoid falls. Little is known about the effect of age on rapid and accurate volitional COP movements. We hypothesized that COP movements to a target would be slower and exhibit more submovements in older versus younger adults, particularly in posterior versus anterior movements. Healthy older (N=12, mean age=76 years) and young women (N=13, mean age=23 years) performed anterior and posterior lean movements while standing on a force plate, and were instructed to move their COP 'as fast and as accurately as possible' using visual feedback. The results showed that rapid posterior COP movements were slower and had an increased number of submovements and ratio of peak-to-average velocity, in comparison to anterior movements (p<.005). Moreover, older compared to younger adults were 27% slower and utilized nearly twice as many compensatory submovements (p<.005), particularly when moving posteriorly (p<.05). Older women also had higher ratios of peak-to-average COP velocity than young (p<.05). Thus, despite moving more slowly, older women needed to take more frequent submovements to maintain COP accuracy, particularly posteriorly, thereby providing evidence of a compensatory strategy that may be used for preventing backward falls.