Dual-task interference during gait on irregular terrain in people with Parkinson's disease

Background: Gait impairments in people with Parkinson's disease (PD) are accentuated in dual-task conditions. Most PD studies on dual-task gait have measured only straight line walking and treadmill gait. Gait alterations on irregular terrain are poorly understood. Research question: To what extent does walking on irregular terrain exacerbate dual-task interference in people with PD, compared to age-matched control participants? Methods: Gait data were collected for nine participants with mild to moderate PD and nine healthy age-matched participants on regular and irregular terrains. Gait was tested as a single task and in dual-task conditions with serial 7 subtractions. The spatiotemporal variables (speed, cadence, single limb support, step length and width), kinematic variables (range of motion for hip, knee and ankle joints) and stability variables (trunk range of motion and center of mass acceleration RMS) were compared across conditions. Results: People with PD showed reduced gait speed and cadence and increased mediolateral center of mass acceleration when walking on irregular terrain with dual-tasks. Surface irregularity was associated with increased ankle transverse motion in both groups. Increased hip and knee sagittal motion was observed in the control participants when terrain changed from regular to irregular under dual-task conditions. This was not statistically significant for the PD group. Significance: Dual-task walking on irregular terrain exacerbated the gait deficits, particularly for people with PD. Gait speed, cadence and mediolateral body stability were compromised when people with PD walked on irregular terrain whilst performing dual-tasks. There was an increase in ankle transverse motion in both groups when traversing irregular terrain. This might have been an adaptive strategy, to prevent tripping.