Twenty-four-hour movement composition is associated with HR-pQCT bone strength in older adults: The Study of Muscle,...

Time in moderate-to-vigorous intensity activity (MVPA), light intensity activity (LPA), and sleep are critical for bone health in older adults but are often considered separately despite being inherently co-dependent. We examined cross-sectional associations between compositions of accelerometry-derived MVPA, LPA, inactivity, and sleep with bone microarchitecture and strength (High-Resolution Peripheral Quantitative Computed Tomography; HR-pQCT) in community-dwelling older men (n=119) and women (n=177), mean age 76.3±4.6 yrs. Participants wore an ActiGraph GT9X on their non-dominant wrist for 7 consecutive 24hr periods during the Study of Muscle, Mobility and Aging (SOMMA) baseline visit. The primary outcomes were distal radius (DR) and tibia (DT) estimated failure load, and secondarily, total volumetric bone mineral density (vBMD), and cortical (Ct) and trabecular (Tb) vBMD, area (Ar), and thickness (Th) from HR-pQCT. Compositional data analysis methods evaluated proportions of time in one behavior relative to the remaining behaviors. Sex-stratified multiple linear regression estimated associations between 24hr composition with sex-specific standardized HR-pQCT parameters. Compositional isotemporal substitution methods estimated hypothetical changes in continuous HR-pQCT measures if 10-60 min in one behavior was displaced by another. On average, women spent 90.2 min/day (6.3%) in MVPA, 346.1 min/day (24.0%) in LPA, 556.4 min/day (38.6%) in inactivity, and 447.4 min/day (31.1%) in sleep; men spent 93.6 min/day (6.5%) in MVPA, 309.5 min/day (21.5%) in LPA, 596.7 min/day (41.4%) in inactivity, and 440.2 min/day (30.6%) in sleep. Compared to the average sex-specific 24hr composition, higher proportions of MVPA were associated with higher DR and DT failure load in women; higher DR Tb.vBMD and Tb.Th in men; and higher DR Tt.vBMD, Ct.Ar, and Ct.Th, and DT Ct.vBMD, Ct.Ar, and Ct.Th in women. Hypothetically displacing 10-60 min in inactivity for MVPA resulted in more favorable HR-pQCT parameters. These data support the importance of MVPA for a healthy skeleton in older men and women.