Experimental Setup and Procedure
An overview of the experimental procedure is shown in Overview of the experimental procedure in this study. The experimental procedures were performed in the order of pre-test (a), Intervention (b), and post-test (c). (a) and (c): participants were asked to perform tandem stance on the force plate. Air cylinders perturbed the subjects laterally during tandem stance. (b): The intervention consists of 16 tandem stance exercises in total. The participants in WBED group were perturbed by WBED during tandem stance, while the participants in Sham group were not perturbed.After the pre-test, the participants were asked to perform four sessions of tandem stance exercises. Each session consisted of four one-minute tandem exercises. During the intervention session, participants looked at a sign 2 m away, which was placed at a height corresponding to the height of their eyes. In the WBED group, participants randomly underwent unexpected perturbation in the mediolateral direction by the PAMs. Although the Sham group participants performed the same exercises while wearing the WBED, the PAMs did not contract during the intervention session. Finally, the post-test was conducted in the same manner as the pre-test. Participants were allowed to rest at any time during the experiment. An experimental collaborator was near the participants for fall prevention. Handrails were also set up on both sides of the participant.