Comparisons of a) step length, b) foot angle, c) the center of mass (COM) position, d) COM velocity, e) COM stability, and f) hip height between the treadmill-slip training group (Group A, n = 17) and the over-ground-slip training group (Group B, n = 17). Because these measurements are taken at right foot touchdown during their baseline (unperturbed walking) trials, before (Pre) and after (Post) Group A’s treadmill training (A_5 and A_10) and before Group B’s first slip trial (B_10), they are reflective of the proactive.