Knee Extensor Strength, Dynamic Stability, and Functional Ambulation: Are They Related in Parkinson's Disease?

Nocera JR, Buckley T, Waddell D, Okun MS, Hass CJ. Knee extensor strength, dynamic stability, and functional ambulation: are they related in Parkinson's disease? Arch Phys Med Rehabil 2010;91:589-95. Objective: To evaluate the relationship between knee extensor strength, postural stability, functional ambulation, and disease severity in Parkinson's disease (PD). Design: A cohort study. Setting: University research laboratory. Participants: Patients (N=44) with idiopathic PD. Intervention: Not applicable. Main Outcome Measures: Participants were evaluated on their isokinetic knee extensor strength. Additionally, participants completed an assessment of their postural stability (Functional Reach Test for static stability and a dynamic postural stability assessment as measured by the center of pressure center of mass moment arm during gait initiation). Participants also underwent an evaluation of their functional ambulation as measured by a 6-minute walk test. Lastly, participants were evaluated by a neurologist specially trained in movement disorders to assess neurologic status and disease severity using the Unified Parkinson's Disease Rating Scale and the Hoehn and Yahr disability score. Results: Knee extensor strength positively correlated with dynamic postural stability and negatively correlated with disease severity. Further, dynamic postural stability was negatively correlated to disease severity and positively correlated with functional ambulation in this cohort of patients with PD (P<.05). The results also suggest that the Functional Reach Test may be a valuable assessment tool to examine postural stability in PD. Conclusions: These findings suggest a malleable relationship between knee extensor strength, dynamic stability, and disease severity in PD. Although strength is only one piece of the puzzle in the functional outcome of PD, these findings may assist clinicians in designing appropriate interventions aimed at increasing function and decreasing fall risk in PD.