Self-paced treadmills do not allow for valid observation of linear and non-linear gait variability outcomes in patients with Parkinson's disease.

BackgroundDue to the imposed constant belt speed, motorized treadmills are known to change linear and non-linear gait variability outcomes. This is particularly true of patients with Parkinsons disease where the treadmill can act as an external pacemaker. Therefore, the use of treadmills is generally not recommended when quantifying gait variability. Self-paced treadmills allow for updating the belt speed relative to the walking speed of the subject and might, therefore, be a useful tool for the collection of long consecutive walking trials, necessary for gait variability observations. Research questionTo validate gait variability measures collected on a self-paced treadmill as compared to overground walking. MethodsThirteen healthy subjects and thirteen patients with Parkinsons disease performed 5 - 8 minute long walking trials: overground, on a treadmill at a constant speed, as well as in three different self-paced treadmill modes. Stride times and stride lengths were recorded using a validated IMU-system and variability was quantified using the coefficient of variation, sample entropy, and detrended fluctuation analysis. Overground and treadmill trials were compared using Pearsons correlation coefficient, method error, and Bland and Altman analysis. ResultsFor healthy subjects, the self-paced treadmill resulted in increased correlation coefficients of 0.57 - 0.74 as compared to a constant speed treadmill. Correlation coefficients for stride length variability between overground and treadmill walking were not significant. For patients, generally, large errors of 33-40% of stride time variability were observed between overground and treadmill walking. Stride length variability is most similar at a constant belt speed and shows errors of 14-39%. SignificanceDespite an improvement of temporal gait variability validity in the self-paced mode for healthy subjects, the large systematic and random errors between overground and self-paced treadmill walking prohibit meaningful gait variability observations in patients with Parkinsons disease using self-paced treadmills.