Supplementary Material for: Effect of Surface Perturbation Treadmill Training Program on Strategies and Kinematics of Reactive Stepping during Standing in Older Adults: A Single-Blinded Randomized Controlled Trial

Introduction: perturbation-based balance training reduces fall rates dramatically by triggering and improving balance recovery skills. We aimed to investigate whether multidirectional surface perturbation treadmill training, which explicitly challenges age-related impairments in reactive responses, can improve balance recovery responses in standing and reduce annual falls. Methods: This was a two-arm parallel-group randomized controlled trial with concealed allocation, blinded assessors, data analyzers, and intention-to-treat analysis. Fifty-three older adults aged 80.1±5.2 years, living in retirement housing, were randomized into two groups: 1) surface perturbation-based hands-free treadmill training (SPTT, n=27) and control group, hands-free treadmill walking training without perturbations (TT, n=26). Both received a 12-week, 24-session training program. For primary outcomes, we evaluated balance recovery, pre- and post-intervention, by stepping thresholds, percent of stepping responses, total probability of stepping, and kinematics of reactive stepping to lateral-surface perturbations in standing. Fall incidents were monitored prospectively one year after training for a secondary outcome. Results: Both groups showed a significant decrease in the percentage of multiple-step responses (p=0.013) and a shorter total recovery time to recover balance (p=0.006). Compared with the TT, the SPTT led to a more significant reduction in single-step and multiple-step thresholds (p=0.003 and p=0.002, respectively), total probability of stepping (p=0.008), shorter first-step length (p=0.003), total steps path length (p=0.007) and decreased total center of mass (CoM) displacement (p=0.040) during recovery stepping. One-year prospective fall monitoring revealed nine fall events in the SPTT group compared to 17 in the TT group. Although these numbers are insignificant, they imply a potential generalization that SPTT can reduce annual falls. Conclusion: A 12-week SPTT reduces the risk of falls by improving reactive balance responses in retirement-housing older adults. Findings suggest that the primary benefit of SPTT was better control in the CoM following perturbations. This study addressed the generalizability of PBT benefits from walking to standing and the personalization of perturbation training to enhance effectiveness and real-life applicability.