Abstract
BACKGROUND: Individuals with early-stage Parkinson's disease (PD) typically do not exhibit impaired balance during clinical assessments; but subtle impairments may exist during challenging dynamic tasks that are not immediately apparent. 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.