Balance control during continuous rotational perturbations of the support surface.

This research investigated the effects of continuous rotational perturbations of the support surface on postural control strategies adopted to maintain upright stance. Four different sinusoidal rotations of the support surface were employed: 0.5 Hz, at 2 degrees; 1.0 Hz at 1 degrees; 1.5 Hz at 4 degrees; and 2 Hz at 3 degrees. Thereby two different velocities of perturbation were obtained: 3.1 degrees s(-1) for 0.5 and 1 Hz, and 18.9 degrees s(-1) for 1.5 and 2 Hz. Results indicate that for the frequencies tested, the effect of the perturbation was attenuated. The amplitude of the body's center of mass (COM) displacement was reduced by adopting a multi-segmental strategy which employed anti-phase ankle and hip joint motion. Our results suggest that at least a two-link model of human stance is required to explain responses when the support surface is rotating.