The role of head-in-space stability on stepping reactions in young and elderly adults.

This study compared head kinematic responses and step latency following an anteriorly directed postural perturbation between two groups (Young, mean age 27.39; Elderly, mean age 71.9). We further attempted to demonstrate, for the first time, a positive linear relationship between sagittal plane head angular velocities and stepping responses in both groups. It was hypothesized that the Elderly would demonstrate higher head angular velocities and greater step latencies than the Young. We also hypothesized that a positive linear relationship would show that, following a perturbation, trials where head angular velocity was low yielded quicker step responses. Each participant experienced three perturbations under five different visual conditions designed to alter visual input and head/trunk coordination. Repeated-measures ANOVA was used, with α set at 0.05. For each test condition, the Elderly consistently demonstrated longer step latencies while exhibiting higher head angular velocities. For each group, a positive linear relationship was shown between the two dependent variables (Young: r=0.86; Elderly, r=0.84). During a postural perturbation, as head angular velocity increased, stepping responses were delayed.