Effects of slipping-like perturbation intensity on the dynamical stability.

Falls are a major cause of morbidity and death in elderly people. Understanding how subjects maintain stability while walking or while being exposed to perturbations is important in order to prevent falls. Here, five healthy subjects were asked to manage unexpected slipping-like perturbations of increasing intensities (i.e., soft, medium and strong) in order to investigate the effects of the perturbation intensity on the biomechanical behavior and on the dynamical stability, described by the Margin of Stability. The lower limb kinematic (i.e., hip, knee and ankle joints angles) was computed before and after the onset of the perturbation. The compensatory time and the Margin of Stability were calculated after the onset of the perturbation. As expected, results showed that the perturbation altered the subjects' kinematic and the modulation of the perturbation intensity was reflected in the dynamical stability: the stronger was the perturbation, the lower was the Margin of Stability describing a lower balance recovery.