Biomechanical and strength factors underlying performance of the sit-to-stand task in persons with Parkinson's disease

Purpose: Up to 80% of individuals with Parkinson's disease (PD) report having difficulty with rising from a chair. The purpose of this study was to 1) quantify how sit-to-stand (STS) performance differs between persons with PD and age-matched controls, and 2) determine if there is a relationship between lower extremity strength and performance of STS. Methods: Ten male subjects with PD (64.1 ± 10.1 years) and ten male age-matched controls (65.5 ± 12.4 years) participated. Subjects were instructed to rise from a backless, knee-height chair without the use of their arms. Subjects with PD were tested on two separate days in an on and off-medication state. Lower extremity and trunk movements and muscle activity (EMG) were recorded, in addition to forces under the buttocks and feet. A Kin-Com strength dynamometer was used to measure concentric, isokinetic knee and hip extensor torque. Paired t-test assessed differences between groups for 1) biomechanical parameters during the STS and 2) torque from the strength dynamometer. Pearson product correlations were used to assess the relationship between strength (torque) and STS performance (duration). Results: For the STS, the movement duration, EMG, joint-angles and joint moments (timing and magnitude) were similar between subjects with PD and controls except for a lower and earlier (prior to lift-off of the buttocks) peak knee extensor moment and absence of preparatory abdominal activity in subjects with PD. Hip and knee strength, as assessed by isokinetic torque, was generally lower for subjects with PD. Greater hip strength was related to better STS performance in subjects with PD and greater knee strength was related to better STS performance in controls. Conclusions: Lower extremity weakness, in addition to altered preparatory activity (early and low peak knee extensor moment and lack of abdominal activity) may contribute to the difficulties that individuals with PD have in rising from a chair. In addition, these findings suggest that performance of the STS task in subjects with PD is more dependent on the hip than on the knee strength.Medicine, Faculty ofGraduat