Compositional data analysis of 24hr activity and its associations with muscle strength and power: The Study of Muscle, Mobility and Aging

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BACKGROUND: Physical activity (PA) and inactivity have opposing associations with skeletal muscle function and are often studied separately but are codependent. We evaluated cross-sectional associations between 24-h time-use behaviors with muscle strength and power. METHODS: Sample included 751 community-dwelling older adults (76 ± 5 years, 57% women). Compositional data analysis determined 24-h proportions of time in moderate-to-vigorous PA (MVPA) and light intensity PA (LPA), inactivity, and sleep. Multiple linear regression by sex evaluated associations between 24-h composition with stair climb ascend and leg press power (W), and leg press (lbs) and grip strength (kg). Compositional isotemporal substitution quantified hypothetical reallocations of time between behaviors on power and strength. RESULTS: Compared to the average 24hr day in women (MVPA: 84 min/day, LPA: 349 min/day, inactivity: 559 min/day, sleep: 448 min/day), higher 24-h proportions of MVPA were associated with higher stair climb power (β: 16.2, 95% CI: 10.9, 21.4), leg press power (β: 23.7, 95% CI: 10.3, 37.2), and leg strength (β: 8.5, 95% CI: 2.4, 14.6); higher 24-h proportions of LPA were associated with lower stair climb power (β: -14.4, 95% CI: -25.8, -3.0); and higher 24-h proportions of inactivity were associated with higher grip strength (β: 2.3, 95% CI: 0.4, 4.3). Compositional isotemporal substitution found reallocating 10 min from LPA or inactivity to MVPA supported higher power and strength. No associations were observed in men. CONCLUSIONS: In women, not men, 24-h movement composition was associated with power and strength. MVPA interventions for power and strength improvements in women may be optimized when LPA or inactivity are reduced, not sleep.

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