Short-term effects of posture-assisted step training on rapid step initiation in Parkinson's disease.

BACKGROUND AND PURPOSE Anticipatory postural adjustments (APAs) for lateral weight transfer and stability precede and accompany gait initiation. Individuals with Parkinson's disease (PD) show altered APA characteristics with delays in initiating stepping that may reflect impaired interactions between posture and locomotion. The purpose of this study was to determine the short-term effects of a single session of repetitive robotic assistance training with the APA on rapid step initiation in individuals with PD in the medications "on" state and healthy control individuals. Ground reaction forces and step kinematics were recorded. METHODS Subjects first performed baseline trials of unassisted self-paced rapid forward stepping. Next, a training acquisition series involved 50 trials with a lateral pull applied to the pelvis by a robotic system to assist with the early phase of the APA during stepping. To assess potential retention effects of training, unassisted stepping trials were evaluated immediately after acquisition trials (immediate retention) and one week later (one-week retention). RESULTS Overall, the subjects with PD had a longer APA duration (P < 0.03), and longer first step duration (P < 0.04) than the healthy control individuals. Compared with baseline, APA duration was shorter (P < 0.001) and step onset time became earlier (P < 0.001) for acquisition trials but these effects were not retained. Step duration, which became shorter (P < 0.001) during the late acquisition trials (P = 0.002), demonstrated immediate retention (P < 0.001) and one-week retention (P < 0.001). CONCLUSION Posture-assisted training, affecting the interaction between posture and locomotion, may have therapeutic potential for improving movement performance in individuals with PD.