Effects of On- and Off-Medication Periods on Walking Performance in Parkinson's Disease: Insights from Movement Synergies.

Introduction: Impaired walking performance significantly impacts the quality of life in individuals with Parkinson's disease (PD). This study aimed to examine the effects of medication "on" and "off" periods on walking performance, focusing on an alternative aspect of traditional gait analysis by assessing movement components or synergies (i.e., principal movements, PMs).

Methods: Principal component analysis was used to decompose kinematic marker data from 22 PD patients (64.1 ± 10.5 years) during self-selected speed overground walking into a set of PMs that cooperatively contribute to the locomotion task. Gait adaptation between medication periods was assessed using two PM-based variables: relative explained variance (rVAR) of the PM's position, reflecting movement structure, and root mean square (RMS) of the PM's acceleration, indicating movement acceleration magnitude and reflecting changes in force or speed.

Results: The on-medication condition increased the contribution (greater rVAR) of PM₂, representing the swing-phase movement component (p = 0.001), and enhanced movement acceleration magnitudes (greater RMS) in PM₄, characterizing the single-leg support phase coupled with trunk rotation (p = 0.026).

Conclusion: Although medication enhances propulsion by increasing the contribution of swing-phase movement components, thereby improving forward movement and walking efficiency, it may also lead to instability during the single-leg stance phase.