Gait initiation and dynamic balance control in Parkinson's disease

Objective: To determine whether the magnitude of the separation between the center of pressure (COP) and the whole-body center of mass (COM) during gait initiation can differentiate patients with varying severity of Parkinson's disease (PD) disability. Design: Cross-sectional, intact groups research design. Setting: Biomechanics research laboratory. Participants: Forty-three patients were stratified into 2 groups based on the Hoehn and Yahr (H&Y) disability score, which heavily favors balance in determining disability. The 2 groups were: H&Y score of 2.0 or less (n = 23; age, 61+/-10y) or H&Y score of 2.5 or higher (n=20; age, 70+/-9y). Interventions: Not applicable. Main Outcome Measures: The peak COP-COM distance represents the maximum separation between the location of the whole-body COM and the ground reaction force's COP, and thus is an indicator of dynamic balance control. The peak COP-COM was evaluated during 3 phases of the COP trajectory during a gait initiation task. Results: The peak magnitude of the COP-COM distance was significantly greater during the end of the single-support phase in the less disabled patients (H&Y score <= 2.0) than in more balance disabled patients (H&Y score >= 2.5) (P = .004). Conclusions: The differences in COP-COM distances between these H&Y groups suggest that patients with PD who have impaired Postural control produce shorter COM-COP distances than do persons without clinically detectable balance impairment. This method of evaluation could prove a useful quantitative index to examine the impact of interventions designed to improve ambulation and balance in PD.