Lateral weight transfer deficits reveal balance vulnerability in early-stage Parkinson’s Disease during trip-perturbed walking

Background Individuals with early-stage Parkinson’s disease (PD) typically exhibit normal balance during clinical assessments; but subtle impairments may exist during dynamic tasks. Objective This study investigates reactive balance responses to trip perturbations during walking in early-stage PD compared to age-matched controls. Methods Sixteen individuals with early-stage PD (Hoehn & Yahr 2-2.5) and sixteen age-matched controls walked on a treadmill, experiencing an unpredictable trip perturbation. Whole-body kinematics were analyzed to compute margin of stability (MoS) and lateral body center of mass (COM) displacement trajectories across four reactive steps. Statistical comparisons evaluated group differences in MoS and COM displacement, while correlation analyses assessed relationships between stability and lateral COM displacement. Results By the third recovery step, controls had regained stability, while PD participants displayed significant variability. Half of the PD group exhibited negative MoS values, indicating instability, while the other half maintained stability comparable to controls. Moderate correlations between third-step MoS and lateral COM displacement ( r  > 0.56, p  < 0.01) suggest impaired lateral weight transfer contributes to balance failure in PD. Conclusions This study reveals variability in reactive balance capacity among early-stage PD participants, with nearly half showing subclinical deficits in lateral COM control. Trip-perturbed walking could serve as a promising biomarker for early balance impairments, potentially guiding proactive fall prevention strategies in PD management.