Gait initiation in older adults with postural instability

BACKGROUND: This study examined changes in the translation of the center of pressure during forward and lateral (90 degrees to the side) gait initiation in two populations of older adults with postural instability. METHODS: Twenty-eight older adults transitioning to frailty and 16 persons with Parkinson's disease in the "on medication state" were evaluated during initiation trials. Displacements, velocities, and smoothness of the center of pressure trace were calculated and compared. FINDINGS: Both groups produced movements of the center of pressure that on average were reduced compared to healthy populations. Adults transitioning to frailty were able to scale the output of the motor program so forces that propel the body in the intended direction of movement were maximized as evidenced by movements of the center of pressure. The adults transitioning to frailty produced patterns of center of pressure trajectories that were more similar to healthy adults where as individuals with Parkinson's disease produced trajectories that were counterproductive to producing efficient gait initiation in both the forward and lateral direction. INTERPRETATION: These findings suggest that persons with Parkinson's disease even when in the medicated state exhibit inefficient postural adjustments during both forward and lateral gait initiation and that these postural adjustments are more susceptible to deterioration from the complex interaction of central and peripheral changes associated with Parkinson's disease than to aging alone.