Dynamic stability control during volitional stepping: a focus on the restabilisation phase at movement termination.

This work sought to advance the understanding of dynamic stability control during stepping. The specific intention was to better understand the control of the centre of mass during voluntary stepping, by characterizing its trajectory and intertrial variability. Young participants (n=10) performed five different stepping tasks to vary the challenge to COM control: (1) preferred step, (2) long step, (3) wide step, (4) long and wide step and (5) rapid step. The trajectory of the total body COM during the restabilisation phase was assessed by quantifying the magnitude of incongruity between the peak and final COM position. The intertrial variability of incongruity and the extent to which incongruity was reduced with trial repetition were also evaluated. Interestingly, incongruity was typical during preferred stepping, with a strong bias toward overshoot. In the frontal plane, the magnitude of incongruity and the incidence of overshoot were greater in trials with increased step width. The variability of incongruity did not vary by condition nor was there evidence of adaptive changes. Together, these results suggest that overshoots may represent a strategy linked to gait initiation or to the simplification of reactive control during the restabilisation phase. Further insight into these mechanisms will be gained by examining the kinetic determinants of dynamic stability control.