Biomechanical adaptation to repeated slips during standing in people with Parkinson's disease.

Falls are a major concern in people with Parkinson's disease (PwPD). Although perturbation-based balance training could reduce fall risk, it remains unclear whether PwPD can tolerate and adapt to repeated large-scale stance perturbations. This study examined the feasibility of applying large-scale standing-slips to PwPD and their capacity for rapid adaptation to recurrent slips. Ten PwPD experienced five unexpected standing-slips induced by a standardized-magnitude acceleration-deceleration treadmill perturbation on an ActiveStep treadmill, while wearing a safety harness. Dynamic gait stability and limb support were calculated at slip onset (ON) and at recovery step liftoff (LO) and touchdown (TD), serving as the primary outcome measures. Secondary outcomes included recovery-step latency, duration, length, speed, slip distance, and faller rate. Adaptive changes across trials were assessed using repeated-measures ANOVA or Friedman tests, followed by paired t-tests or Wilcoxon tests, respectively. No participants reported injuries or discomfort related to the slips. They demonstrated significant improvements in dynamic gait stability at ON, LO, and TD (p = 0.005 - 0.017) and limb support (p = 0.010 at LO and 0.020 at TD) across repeated slips. Recovery step latency was shorter in later trials (p = 0.013), accompanied by a reduction in slip distance at LO (p = 0.018). The faller rate declined from 70% on the first slip to 40% on the last (p = 0.187). PwPD tolerated high-intensity standing-slips and rapidly adapted to repeated slips by refining dynamic gait stability, limb support, and recovery step performance during slips. The findings can inform future trials of applying standing-slips to PwPD to reduce their fall risk.