Forward and backward walking in Parkinson disease: A factor analysis

Background: Forward and backward walking are both impaired in Parkinson disease (PD). In this study, an exploratory factor analysis was performed to investigate the relationship between forward and backward walking in PD. Research question: Given the difference in levodopa response between forward and backward walking, what is the additive value of testing backwards walking in a clinical setting. Methods: Sixty-two patients with PD (65.29 +/- 7.17 yrs, UPDRS OFF = 29.68 +/- 9.88, UPDRS ON = 16.40 +/- 8.21) and eleven healthy age-matched controls (63.09 8.09 yrs) were recruited. PD participants completed forward (F) and backward (B) walking tasks on a 6.1 m instrumented walkway (OFF and ON levodopa). Factor analysis was used to derive models for both walking tasks/medication states. Results: In both OFF and ON, four factors were identified: Variability (OFF: F = 30.0%, B = 17.8%, ON: F = 21.6%, B = 25.0%), Rhythm (OFF: F = 14.5%, B = 17.0%, ON: F = 17.4%, B = 19.0%), Asymmetry (OFF: F = 13.7%, B = 14.3%, ON: F = 16.1%, B = 15.2%), and Pace (OFF: F = 12.2%, B = 17.0%, ON: F = 13.9%, B = 8.7%). In the ON state, a fifth factor was identified: Posture (ON: F = 3.8%, B = 7.7%). Significance: This study demonstrates the similarity in gait domain factors in both forward and backward walking. While domains of gait are similar in both walking tasks, levodopa response is reduced in backward walking. This could be a result of the increased complexity of backward walking. This study provides a normative dataset that can be used when assessing forward and backward walking in individuals with PD.