Relating Anticipatory Postural Adjustments to Step Outcomes During Loss of Balance in People With Parkinson’s Disease

Abstract

Background. Effective protective steps are critical for fall prevention, and anticipatory postural adjustments (APAs) after a perturbation but prior to protective steps affect step performance. Although APAs prior to protective steps are altered in people with Parkinson’s disease (PD), whether these changes affect subsequent step performance is poorly understood. Objective. Characterize the relationship between mediolateral APA size and protective step outcomes in response to anteroposterior balance perturbations in people with PD. Methods. Twenty-eight individuals with PD completed 25 forward and 25 backward protective steps in response to support surface translations. Multilevel linear models related mediolateral APA size to protective step outcomes. Results. During forward protective stepping, larger mediolateral APAs were associated with delayed (P < .001) and larger (P = .004) steps. Larger APAs were also associated with smaller mediolateral (P < .001) but larger anterior-posterior center of mass movement at foot off (P < .001). During backward stepping, larger APAs were associated with later steps (P < .001) and smaller anterior-posterior margin of stability at first foot contact (P < .001). During backward stepping, larger APAs were also associated with worse clinical (ie, UPDRS [Unified Parkinson’s Disease Rating Scale]; P = .005) and balance (ie, MiniBEST [Mini-Balance Evaluation Systems Test]; P = .021) outcomes. Conclusions. During forward protective stepping, larger APAs were associated with larger and later steps, suggesting APA size may have mixed effects on the subsequent step. During backward stepping, larger APAs were associated with worse stepping outcomes (ie, later steps, smaller anterior-posterior margin of stability, worse clinical outcomes). Interventions aimed at improving APAs in PD should monitor spatial and temporal protective step outcomes to ensure treatment does not negatively affect protective steps, particularly for forward stepping.