Movement Velocity in the Sit-to-Stand Task in Adults with Prader-Willi Syndrome

Prader-Willi syndrome (PWS) is a rare congenital disorder that leads to obesity and poor muscular development, making daily tasks like raising from a chair difficult. The key parameters to successfully transitioning from sitting to standing are lower limb power and balance. PURPOSE: This study aims to determine differences in velocity during the sit-to-stand (STS) in adults with PWS and examine its relationship to muscular force. METHODS: Participants were ten adults with PWS [7M/3F; 18-40 y/o], ten with obesity [7M/3F; 18-40 y/o], and ten with normal weight (NW) [7M/3F; 18-40 y/o]. A motion camera analysis system collected biomechanical data from reflective markers placed on the ankle, knee, hip, and trunk. Participants completed 3 sets of 5 STS repetitions at a self-selected pace with 2-3 minutes of rest between sets. Velocity of the pelvis segment center of mass was used to estimate movement velocity (m/s). Average and peak vertical velocity were obtained from each repetition during the rising portion of STS task (determined as when the vertical velocity exceeded and fell below 0.2 m/s). Data were averaged across all sets and repetitions for analyses (i.e. 15 repetitions total [3 sets x 5 repetitions]). Lower limb muscular strength was measured using an isokinetic dynamometer, with participants completing three maximal kicking contractions. One-way ANOVAs were used to compare parameters between groups and Pearson product correlations were used to determine associations between movement velocity and muscular strength. RESULTS: The STS average velocity was significantly different between groups (p=.040). The STS peak velocity was not statistically different between the groups (p=.054). The PWS group had a lower STS average velocity (0.61±0.20 m/s) but comparable peak velocity (x̄= 0.85±0.26 m/s) than both obesity (x̄=0.71±0.13 m/s; x̄= 0.98±0.22 m/s) and NW groups [x̄= 0.79±0.08 m/s; x̄= 1.09±0.13 m/s). Additionally, the STS average velocity was strongly and positively related to muscle strength (r=0.702, p<0.001). CONCLUSION: In PWS a lower average velocity when transitioning from sitting to standing may be related to limited muscular force. Performance in the STS appears unrelated to excess body fat, as there were no differences between the group with obesity and the group with NW.