The “ascending-mixed-intensity” treadmill-slip perturbation training protocol. Forty slips were given over eleven blocks at five intensity levels with a larger number indicating a larger slip intensity. The first nine blocks (blocks 1–9) included four slips in each block and the last two blocks (blocks 10 and 11) included two slips in each block. The bolded trials represented trials of study interests (i.e., P1pre in block 1). Specifically, the first trial of each block (i.e., P1pre, P3pre, P4pre, and P5pre) was compared with the first trial of the later block at the same intensity level (i.e., P1post, P3post, P4post, and P5post) to test the pre- and post-training effect (H1). In addition, the first trials of each block (i.e., P1pre, P3pre, P4pre, and P5pre) were compared to test the scaling effect in the ascending session (H2).