082. LEVELS OF PHYSICAL ACTIVITY AND BONE MICROSTRUCTURE IN A UK COHORT OF OLDER ADULTS

Abstract

Background: Physical activity (PA) has previously been shown to be associated with improved musculoskeletal health in later life. Here we investigated patterns of PA impact, divided by level of loading, in older free-living adults, and whether high impact counts were associated with bone microstructure and muscle strength in this population. Method(s): We recruited a randomly selected subset of the Hertfordshire Cohort Study (n=114), a cohort of men and women born 1931-39 who have previously been shown to be representative of the UK population. Subjects wore a tri-axial accelerometer on the waist for 7 days and y-axis peaks were recorded to measure the intensity of weight bearing physical activity. Peaks were classified into low (0.5-1.0g), medium (1.0-1.5g) and high (>=1.5g) impact bands. High resolution peripheral quantitative computed tomography (HRpQCT) was performed at distal tibial and radial sites, grip strength was measured by Jamar dynamometer and a lifestyle questionnaire was completed. Result(s): Sixty-nine men and 45 women were enrolled with a mean (SD) age of 75.3 (2.6) and 75.4 (2.6) years respectively. The recorded median counts decreased with increasing intensity with 6224 (Interquartile Range:2401-13,232) low intensity counts, 189 (IQR 64- 633) medium intensity counts and 38 (IQR 13-112) high intensity counts in this population. Data were analysed unadjusted and then adjusted for gender and BMI. At the radius, low intensity activity counts were positively associated with total area (p<0.001) and trabecular area (p<0.001), which remained robust to adjustment. The same pattern was observed for medium intensity counts for total area (p=0.002) and trabecular area (p=0.001). We identified a negative association with cortical density (p=0.011) and this relationship persisted post-adjustment. We identified a positive association between number of high impact counts with total area (p=0.046) and trabecular area (p=0.036) though this relationship was attenuated after adjustment. At the tibia, similar, although weaker associations were observed. Spearman's rank demonstrated a significant correlation for increasing grip strength and increasing activity counts at low (Spearman's Rho = 0.33), medium (0.29) and high impact activity (0.17). Conclusion(s): Our data suggest that low and medium intensity PA are significantly associated with total bone area and trabecular area in older adults. The negative association of medium intensity impact activity with cortical density may be artifactual due to the thinner cortices. There was a positive correlation between grip strength and number of activity counts at all three levels of impact, supporting previous PA data. High impact physical activity rarely occurred in this elderly population.