Biomechanical Changes During Running on a Lower Body Positive Pressure Treadmill in Competitive Runners

Lower body positive pressure treadmills (LBPPTs) offer precise body weight unloading for injury rehabilitation and performance training in runners. This study investigated biomechanical changes during running at varying body weight support (BWS) levels (0%-80%) in competitive runners, including sex-specific responses. Twenty-six runners (age: 33.6 ± 9.8 years; 15 female, 11 male) completed randomized 3-min running bouts at 12 km/h across nine BWS levels. Spatiotemporal parameters, plantar force, peak tibial acceleration, and running stability were measured using pressure insoles and inertial sensors placed at the tibia and foot. Our results revealed significant reductions in step rate (b = -0.24 steps•min^-1/%BWS, p < 0.001), normalized ground contact time (b = -0.001 1/%BWS, p < 0.001), maximum plantar force (b = -0.010 BW/%BWS, p < 0.001), and peak tibial acceleration (b = -0.03 g/%BWS, p < 0.001) with increased BWS. Swing time increased (b = 1.50 ms/%BWS, p < 0.001), while stance time decreased (b = -0.41 ms/%BWS, p < 0.001). Running stability showed marginal changes (foot: b = -0.001 1/%BWS, p = 0.017; tibia: b = 0.001 1/%BWS, p = 0.009). Sex differences were observed in step rate (b = -6.79 steps•min^-1, p = 0.045) and maximum plantar force (b = -0.128 BW, p = 0.034), but there were no significant sex × BWS interaction effects for any of the investigated parameters. Findings from this study highlight the effectiveness of LBPPTs for reducing musculoskeletal loading while revealing associated gait changes. Athletes, therapists, and coaches should consider individual biomechanical responses to optimize rehabilitation and performance strategies. Future research should explore long-term adaptations and injury prevention outcomes.