Fig. 1.

Schematics of study design to test the transfer of treadmill-training effect. Group A (treadmill-slip-training group) took five trials of spontaneous (and unperturbed) over-ground walk (pre-training baseline trials, from A_1 to A_5) before receiving a minimum of 15 “slip-like” perturbation trials on treadmill. After the treadmill training, these subjects then took another five trials of spontaneous walk (post-training baseline trial, from A_6 to A_10), that were finally followed by an over-ground-slip trial (A_S1). Group B (over-ground-slip-training group) took ten baseline trials (from B1 to B10), followed by a block of eight over-ground slip trials (from B_S1 to B_S8), three non-slip trials, and eight more slips (B_S9 to B_S16). Because both first over-ground slips, A_S1 and B_S1, were equally novel in which subjects did not know when, where, or how a slip could occur, B_S1 served as the control for A_S1 to test Hypothesis One (H1: treadmill training reduces likelihood of falls in over-ground slip). B_S16 represented the post-training trial for over-ground-slip training. The comparisons between A_S1 and B_S16 were used to examine Hypothesis Two (H2: direct over-ground-slip training has greater fall reduction effect than does indirect treadmill-slip training)