Archives of Gerontology and Geriatrics Plus · Nov 2026
Reliability and validity of a simple smartphone-based method for assessing lower-limb function using sit-to-stand acceleration in older adults
By Yamamoto N, Higashionna A, Tateoka K et al.
Background This study estimated trial-to-trial and device-to-device reliability of a simple smartphone web application for measuring sit-to-stand acceleration index without body attachment in older adults and assessed its validity via associations with lower-limb performance tests. Methods Eighty-five older adults (30 men and 55 women; mean age, 74.3 ± 5.3 years) performed a sit-to-stand movement from a 40-cm-high chair while holding a smartphone against their chest. Peak resultant acceleration (PRA), derived from triaxial acceleration (including gravity), was calculated using a smartphone-based web application. Trial-to-trial reliability was assessed from two trials with the same device (n = 85). Device-to-device reliability was evaluated through simultaneous measurements using an iPhone and four Android devices (n = 51). Validity was examined using correlations between PRA and peak ground reaction force (PGRF) during sit-to-stand, knee extension strength, and the Timed Up-and-Go test (n = 85). Results The intraclass correlation coefficients were 0.780 for trial-to-trial reliability and 0.925–0.974 for device-to-device reliability relative to the iPhone. Bland–Altman analysis showed mean differences ranging from −0.047 to 0.557 m/s 2 , with 95% limits of agreement ranging from −1.709 to 2.108 m/s 2 . Proportional bias occurred for one device compared with the iPhone. PRA was correlated with three lower-limb performance measures, with PGRF demonstrating the highest absolute correlation coefficient (r = 0.687, 95% confidence interval, 0.555–0.785). Conclusions PRA demonstrated good trial-to-trial reliability and high device-to-device reliability. In addition, the associations between PRA and established lower-limb performance measures suggest that PRA may reflect certain aspects of lower-limb performance in older adults.