Background and Objectives

Physical fatigability increases with age and may act as a barrier to activity and a marker of functional decline. In older adults, strength-demanding, device-based variables such as free-living sit-to-stand (STS) transitions may be associated with physical fatigability. This study examines STS velocity patterns across a 24-hr cycle and their associations with physical fatigability and functioning in older adults.

Research Design and Methods

This cross-sectional study included a population-based sample of 75-, 80-, and 85-year-old people (n = 479, 60% women). STS transitions were recorded for 3–7 days using a thigh-worn accelerometer, with velocities summarized in two-hour intervals and normalized to daily means. Participants were grouped by self-reported walking fatigability, performance fatigability, and physical functioning. Group differences were analyzed using non-parametric tests and logistic regression, adjusted for age cohort and sex.

Results

Individuals with high self-reported walking fatigability showed greater declines in free-living STS angular velocities in the late afternoon (4–6 p.m.: odds ratio [OR] = 1.39 per 5% decrease, p = .009) than those with low fatigability. Similarly, individuals with high performance fatigability exhibited greater velocity declines in the afternoon and early evening (2–4 p.m.: OR = 1.19, p = .034; 6–8 p.m.: OR = 1.15, p = .035). Evening declines were also most pronounced among those with physical functioning limitations (6–8 p.m.: OR = 1.19, p = .028; 8–10 p.m.: OR = 1.21, p = .003).

Discussion and Implications

Measuring STS velocity decline may help in the identification of older individuals with higher fatigability and poorer physical functioning and may open new possibilities for wearable-based remote monitoring and individualized care.