Variability in the foot-ground clearance and step timing of young and older men during single-task and dual-task treadmill walking.

The study's aim was to document ageing effects on gait control by analysing the distributions of both left and right step timing and minimum foot-ground clearance (MFC) in older men (mean 71.1 years) and gender-matched controls (mean 26.3 years). Step durations and MFC were obtained from continuously sampled 3D markers during preferred-speed treadmill walking (single task) for 15 min and a dual-task condition in which participants walked at the same speed and also responded to the same 90 quasi-randomly presented visual reaction time (RT) stimuli. Significantly longer mean and median RTs were observed when treadmill walking compared to the standing-only control condition. Older males had significantly slower mean RTs for the standing and walking tasks (292 ms and 315 ms, respectively) than the younger group (265 ms and 273 ms). Older males walked more slowly, both groups had greater dual-task step durations but the effect was more pronounced in the older group. Older men's step durations were more positively skewed (longer) while the young had more negative skew. MFC was greater in the older group, and, importantly, in both groups right MFC was greater than the left foot. The data provide evidence of right-left limb asymmetry in preferred speed treadmill walking and it was hypothesised that behavioural slowing in locomotion could be a response to increase the safety of limb end-point control.