The relationship between accelerometer-determined physical activity (PA) and body composition and bone mineral density (BMD) in postmenopausal women

Studies of the relationships between BMD, PA and body composition have shown variable results. Therefore, the aim of this cross-sectional study was to determine the relationships between accelerometer-determined PA and selected body composition parameters to total and regional BMD of the proximal femur in postmenopausal women. BMD and body composition were measured using dual energy X-ray absorptiometry in 97 women with a mean age 63.63 +/- 5.23 years. PA was monitored using an ActiGraph GT1M accelerometer. Correlation analysis did not show significant relationships between PA variables and BMD, but increases in body composition variables were associated with increases in BMD. Lean body mass was the strongest predictor of proximal femur BMD (r = 0.18-0.37), explaining 10% of the variance for total femur, and 3-14% of the variance for regional femurs. Correlations increased when the analysis was controlled for age (r(p) = 0.20-0.39). A significant relationship was also found between body fat mass and BMD (r = 0.16-0.30; r(p) = 0.25-0.37). Analysis of differences between women with normal BMD and osteopenic women showed statistically significant differences in age (p = 0.003; eta(2) = 0.09) and lean body mass (p = 0.048; eta(2) = 0.04). In conclusion, body composition is a stronger predictor of proximal femur BMD than PA variables. However, other studies are necessary to clarify the influence of long-term PA and exercise type on proximal femur BMD. (C) 2012 Elsevier Ireland Ltd. All rights reserved.