Motor and non-motor symptoms impact on different domains of capacity- and performance-related mobility measures in Parkinson’s disease

Motor (MS) and non-motor symptoms (NMS) could contribute to mobility impairment in Parkinson’s disease (PD), but the relative role of each remain unclear. While supervised mobility assessments capture capacity, wearable devices enable evaluation of real-world performance. In this cross-sectional study, 105 individuals with mild-to-moderate PD performed standardized tests of forward, backward walking and turning, and wore a consumer smartwatch for five consecutive days to record average daily steps. MS and NMS were evaluated using validated clinical scales. Robust multivariable regressions showed that MS and NMS explained a modest proportion of mobility variance, with stronger effects on capacity- than performance-related metrics. Tremor-dominant and postural instability/gait disorder subscore predicted supervised mobility, while akinetic-rigid subscore was associated with average daily steps. Executive dysfunction and fatigue emerged as the main NMS determinants of mobility. Overall, these findings suggest a complex interplay between MS and NMS and warrant the need for multidimensional mobility assessment in PD.