Background: Gait speed is an important outcome that relates to mobility, function, and mortality, and is altered in people with Parkinson's disease (PwPD). However, changes in gait speed may not reflect changes in other important aspects of gait.
Objective: To characterize which outcomes change concomitantly with walking speed in PwPD. This information can inform the choice of outcome variables for characterizing and tracking gait performance in this population.
Methods: 67 PwPD and 40 neurotypical adults completed 2-minute overground walking bouts at comfortable and fast self-selected speeds. Eight inertial sensors were used to characterize gait and turning. We identified a subset of participants (38 per group) where the PD participant's "fast" walk was similar speed to neurotypical participants "comfortable" walk, facilitating an across-group gait comparison controlling for gait speed.
Results: Walking at fast gait speed compared to comfortable lead to significant changes in stride length, cadence, and stride time variability, but not in steps to turn, trunk ROM, and trunk and lumbar stability in PwPD. Sub-group analyses showed that despite walking at a similar speed as neurotypical adults, PwPD exhibit altered turning outcomes, lumbar stability, and stride length/cadence.
Conclusions: Gait speed is a critical outcome for characterizing mobility. However, in PwPD, several important outcomes do not exhibit a uniform relationship with gait speed, and remain altered compared to neurotypical adults despite "normalizing" walking speed. Given the complex relationship between gait speed and other gait quality measures, care should be taken when choosing outcome measures to characterize the breadth of gait abnormality in PwPD.
Keywords: Gait; Parkinson’s disease; kinematics; speed.