Sensor- and equation-based sit-to-stand power: The effect of age and functional limitations

Estimating lower-limb muscle power during sit-to-stand (STS) tests is feasible for large-scale implementation. This study investigated 1) whether age, functional limitations and sex have an influence on the movement strategy and power production during STS; and 2) potential differences between STS power estimated with either a simple equation or a sensor. Five-repetition STS data of 649 subjects (♂352 ♀297) aged 19 to 93 years were included. Subjects were divided in different age groups and levels of functioning. A body-fixed sensor measured (sub)durations, trunk movement (flexion/extension) and STS muscle power (P_sensor). Additionally, mean STS muscle power was calculated by a mathematic equation (Alcazar et al., 2018b)Results revealed that 1) older subjects and women showed greater trunk flexion before standing up than younger subjects and men, respectively (both p < 0.001); 2) well-functioning adults seemed to have the tendency to not extend the trunk fully during the sit-to-stand transition (mean difference extension - flexion range = -15.3° to -13.1°, p < 0.001); 3) mobility-limited older adults spent more time in the static sitting and standing positions than their well-functioning counterparts (all p < 0.001); 4) STS power decreased with age and was lower in women and in limited-functioning subjects compared to men and well-functioning subjects, respectively (p < 0.05); 5) P_formula was highly related to P_sensor (ICC = 0.902, p < 0.001); and 6) P_formula demonstrated higher values than P_sensor in well-functioning adults [mean difference = -0.31 W/kg and -0.22 W/kg for men and women, respectively (p < 0.001)], but not among limited-functioning older adults. To conclude, this study showed that age and functional limitations have an influence on the movement strategy during a 5-repetition STS test. Differences in movement strategy can affect the comparison between P_formula and P_sensor. In well-functioning older adults, P_formula was slightly higher than P_sensor, which might be related to an incomplete extension in the sit-to-stand transition.