Total and femoral neck bone mineral density and physical activity in a sample of men and women

Physical activity (PA), total body fat (TBF), and lean body mass (LBM) are associated with bone mineral density (BMD). However, the independent influence of PA on BMD, while controlling for body composition is not understood as well and is the purpose of the current study. Whole-body BMD (g.cm(-2)), femoral neck BMD (g.cm(-2)), TBF (kg), and LBM (kg) were measured with dual-energy X-ray absorptiometry. PA levels (total, work, sport, non-sport) were estimated using the Baecke questionnaire. General linear models determined the independent effects of PA on BMD (whole-body and femoral neck), with adjustment for age, sex, ethnicity, smoking, menopausal status (as appropriate), LBM, and TBF. These associations were also examined by sex and age group (20-34, 35-49, and 50-64 years). The sample included 802 adults (65% women; 13% African American) from the Pennington Center Longitudinal Study that were 20 to 64 years of age (mean +/- SD: 46.9 +/- 11.0 years). Higher sports scores were associated with higher femoral neck BMD in the total group, men and women, and in 20- to 34-year-olds and 35- to 49-year-olds, but not significant in those 50-64 years of age. Similar significant associations were found for sports score with total body BMD; however, this relationship was not significant for women or for those 50-64 years of age. Total PA had inconsistent relationships with both femoral neck BMD and total body BMD. Higher levels of sport-related PA are associated with higher femoral neck BMD; however, these relationships vary by PA domain and site of BMD measurement.