Fig. 4.

Ellipse fits for extrapolated center of mass (COM_x) from two representative participants after downward and backward perturbations. Blue lines identify COM_x antero-posterior (A-P) and medio-lateral (M-L) displacements. 95% confidence ellipses appear in red. Characteristic minor and major axes are shown as dotted lines. Ellipse features following forward perturbations were similar to those after backward perturbations. Minor and major axis angles were near 0° and 90° respectively, suggesting a dominant anterior-posterior postural reaction