Stepping down backwards as a means of detecting biomechanical differences between healthy older and younger adults

Changes in sensory- motor systems that occur with age result in a decrease in postural equilibrium, which has been linked with an increased risk of falling in the elderly. Stepping down backwards from a step perturbs dynamic postural equilibrium, thus offering an opportunity to analyze the biomechanical parameters underlying the control of balance. The aim of this study was to analyze modifications in motor patterns used by older adult subjects to control equilibrium under the environmental constraint of a backward stepping-down movement.

Ten healthy young adult and 10 healthy older adult subjects with no previous history of falls stepped down backward from a stable position on a force plate 7 cm high, at a spontaneous velocity. Each subject performed five trials, and the mean of all trials was used for subsequent analyses. An ANOVA was performed, with temporal parameters defining the phases of the stepping-down backward movement, center of mass velocity, vertical ground reaction force, impulse, and slope as dependent variables, and subject group as independent variable.

Older adult subjects had a longer total movement duration, a longer phase of anticipatory postural adjustments, and a longer weight-transfer phase than young adult subjects (p<0.05). In contrast, older adults had a shorter relative swing phase than the young adults (p<0.05) and a lower center of mass velocity, impulse and slope (p<0.05) than young adults.

To counterbalance the perturbation of postural equilibrium created by the backward stepping-down movement, older adults decreased the intensity of ground reaction forces and spent correspondingly more time in double-support phases than young adults.