UC Davis

Our aim was to determine the association between objectively measured physical activity (PA) and bone strength of the distal limbs among older men. We studied 994 men from the MrOS cohort study (mean age 83.9) who had repeat (Year 7 and 14) 5-day activity assessment with at least 90% wear time (SenseWearPro3 Armband) and Year 14 measures using high resolution peripheral quantitative tomography (HR-pQCT) (Scanco). Total energy expenditure (TEE), total steps per day, peak cadence (mean of top 30 steps/min over 24 h) and time spent in a given level of activity: sedentary (reference, <1.5 metabolic equivalents of task [METs]), light (1.5 to <3 METs), or moderate to vigorous physical activity(MVPA: ≥3 METs) were calculated as mean over the two time points. Estimated failure load was determined from HR-pQCT data using finite element analysis. We used standardized variables and adjusted for potential confounders using linear regression. The means ±SDs for daily activity were: 2338 ± 356 kcal/d [TEE]; 5739 ± 2696 steps/day [step count], 60 ± 20 cpm [peak cadence], 67 ± 28 min/d [light activity], and 85 ± 52 min/d [MVPA]. Higher TEE, step count, and peak cadence were each associated with higher failure load of the distal radius (effect sizes respectively: 0.13 [95% CI: 0.05, 0.20], 0.11 [95% CI: 0.04, 0.18], and 0.08 [95% CI: 0.01, 0.15]) and higher failure load of the distal tibia (effect sizes respectively 0.21 [95% CI: 0.13, 0.28], 0.19 [95% CI: 0.13, 0.26], 0.19 [95% CI, 0.13, 0.25]). Time spent in MVPA vs. time sedentary was related to bone strength at both sites after adjustment, whereas time spent in light activity vs. time sedentary was not. TEE was associated with compartmental area and BMD parameters at distal tibia, but only area parameters at the distal radius. In summary, MVPA over a 7-year period of time may have a modest association with bone strength and geometry among older men.