Postural control during a sit-to-stand task in individuals with mild Parkinson's disease.

Individuals with Parkinson's disease (PD) typically have difficulty rising from a chair. A major contributing factor may be altered anticipatory postural control; this hypothesis has been fueled by reports of altered function of the supplementary motor area in PD, an area linked to the preparation of movements. This study tested the hypothesis that individuals with PD would exhibit altered anticipatory postural control which would include a reduced preparatory hip flexion and decreased forward displacement of the COM prior to lift-off of the buttocks from the chair. Ten male subjects with PD and ten male age-matched controls were instructed to rise from a chair without the use of their arms at their comfortable pace on two separated days during on and off-medication states. Body movements were recorded with an optoelectronic device, in addition to forces under the buttocks and each foot to calculate lower extremity joint angles, joint movements and net body centre of mass displacement (COM). The sit-to-stand (STS) duration was the same for the PD-on and controls, but greater for the PD-off group. The PD groups (on and off) used a hip flexion strategy (greater preparatory hip flexion displacement and forward COM displacement, reduced knee extensor moments) compared to the controls. Contrary to predictions, subjects with PD exaggerated, rather than reduced, the movement preparation of the STS using a hip flexion strategy. Possible underlying causes of this flexion strategy could include compensation for poor lower extremity muscle strength and a need for greater postural stability during the lift-off phase.