Challenging stability limits in old and young individuals with a functional reaching task

The aim of this study was to evaluate the extent to which adding a challenge to a reach test would increase the limit of stability (LOS) in young and old individuals.

While standing on a force plate, with infrared markers on bony landmarks for motion analysis, 15 old (mean [SD], 70 [7] yrs old) and 15 young (mean [SD], 24 [2] yrs old) participants completed the modified functional reach test, in which they were asked to touch the farthest target possible in a series. They were then challenged to touch additional targets (functional reach challenge test) until they lost balance.

The young participants reached farther than the old participants on both the modified functional reach and functional reach challenge tests (P = 0.005 and P = 0.003), but no group differences were found in absolute distance gains seen with the addition of the challenge. The participants in both groups displaced the center of pressure farther and used 10% more of their anatomic stability allowance in the functional reach challenge test than in the modified functional reach test. The young participants increased the LOS from 80.5% to 90.9% of their anatomic allowance, whereas the old participants increased theirs from 72.1% to 82.8%.

The challenge improved reaching and LOS similarly in the young and old participants, but the old participants used smaller absolute percentages of LOS. Knowing the flexibility of LOS is useful for rehabilitation practitioners in assessing balance and designing therapeutic exercises that challenge stability during performance of functional arm movements and train individuals to use their LOS safely.