Beyond Quiet Stance: The Role of Levodopa in Prolonged Standing in Parkinson's Disease

Prolonged standing demands continuous postural adjustments to redistribute weight and maintain comfort. People with Parkinson's disease (PwPD) may show impaired adaptability due to motor symptoms and rigidity. The effects of dopaminergic medication on postural control during prolonged standing are not well understood. This study aims to analyze the impact of dopaminergic medication on postural control during prolonged standing in PwPD, focusing on both global sway characteristics and discrete postural adjustments.

Twenty-two PwPD (Hoehn and Yahr II-III) performed a 15-min standing task on a force plate in randomized ON (medicated) and OFF (unmedicated) sessions. Global sway parameters (sway area, root mean square, velocity, and frequency) and discrete postural adjustments (shifts, fidgets, and drifts) were calculated from center of pressure data. Nonparametric and parametric tests compared ON and OFF states.

In the ON state, participants showed significantly larger sway area, increased root mean square and velocity in anterior-posterior and mediolateral directions, and higher sway frequency (all p < .05). The number and amplitude of discrete adjustments were greater in the ON state, especially anterior-posterior drifts and mediolateral shifts. These changes indicate enhanced postural dynamics under dopaminergic medication.

Dopaminergic therapy promotes a more dynamic and adaptable postural control strategy during prolonged standing in PwPD. Rather than reflecting instability, increased sway and frequent adjustments suggest adaptive behaviors facilitating comfort and stability over time. These findings underscore the value of prolonged standing tasks for assessing postural control and guiding rehabilitation strategies in PwPD beyond what short static tests capture.