Abstract
BACKGROUND AND OBJECTIVES: Mobility can decline in middle age and growing evidence highlights the importance of assessing mobility at this stage of life. Smartphone-based accelerometry during sit-to-stand has been shown to identify mobility impairments, but its utility in detecting subtle mobility deterioration in middle age has not been tested. This study aimed to examine whether smartphone-based accelerometry data measured during sit-to-stand tests performed on a regular chair and a cushioned sofa could be useful for detecting subtle changes in mobility in middle age. RESEARCH DESIGN AND METHODS: Twenty-three young (25.0 ± 2.5 years), 25 middle-aged (52.0 ± 5.2 years), and 17 older adults (70.0 ± 4.1 years) performed the 5-times sit-to-stand test on both a standard chair and a sofa. A smartphone attached to the participants' lower back was used to measure lower-limb muscle power, maximal vertical velocity (MVV) during rising, the duration of the total task and the subphase of transition from sitting to standing (SiToSt), and repetition variability using the dynamic time warping method. RESULTS: Middle-aged adults had reduced lower-limb muscle power compared to young adults (5.25 ± 1.08 vs 6.19 ± 1.38 W/kg, p = .034), being more pronounced on the sofa (6.23 ± 1.61 vs 8.08 ± 2.17 W/kg, p = .004). Differences between middle-aged and young adults in terms of MVV (p = .011) and SiToSt duration (p = .038) were only detected on the sofa, and the middle-aged adults showed less variability compared to the older adults on the chair (p = .018). There was no difference in total task duration between the middle-aged group and the young or older adults in either condition. DISCUSSION AND IMPLICATIONS: Most common tests are limited in their ability to detect early mobility deterioration in midlife due to a ceiling effect. Our results, which show the potential of smartphone-based sit-to-stand assessment in detecting subtle mobility decline in midlife, could serve as a screening tool for this purpose.