Sit-to-stand muscle power test: Comparison between estimated and force plate-derived mechanical power and their association with physical function in older adults

Objectives: This study aimed i) to assess the assumptions made in the sit-to-stand (STS) muscle power test [body mass accelerated during the ascending phase (90% of total body mass), leg length (50% of total body height) and concentric phase (50% of total STS time)], ii) to compare force plate-derived (FPD) STS power values with those derived from the STS muscle power test; and iii) to analyze the relationships of both measurements with physical function. Material and methods: Fifty community-dwelling older adults (71.3 +/- 4.4 years) participated in the present investigation. FPD STS power was calculated as the product of measured force (force platform) and velocity [difference between leg length (DXA scan) and chair height, divided by time (obtained from FPD data and video analysis)], and compared to estimated STS power using the STS muscle power test. Physical function was assessed by the timed-up-and-go (TUG) velocity, habitual gait speed (HGS) and maximal gait speed (MGS). Paired t-tests, Bland-Altman plots and regressions analyses were conducted. Results: Body mass accelerated during the STS phase was 85.1 +/- 3.8% (p < 0.05; compared to assumed 90%), leg length was 50.7 +/- 1.3% of body height (p < 0.05; compared to 50%), and measured concentric time was 50.3 +/- 4.6% of one STS repetition (p > 0.05; compared to assumed 50%). There were no significant differences between FPD and estimated STS power values (mean difference [95% CI] = 6.4 W [-68.5 to 81.6 W]; p = 0.251). Both FPD and estimated relative (i.e. normalized to body mass) STS power were significantly related to each other (r = 0.95 and ICC = 0.95; p < 0.05) and to MGS and TUG velocity after adjusting for age and sex (p < 0.05). Conclusions: Estimated STS power was not different from FPD STS power and both measures were strongly related to each other and to maximal physical performance.