Physical activity and bone mineral density at the femoral neck subregions in adolescents with Down syndrome

Background: Low bone mineral density (BMD) has been frequently described in subjects with Down syndrome (DS). Reduced physical activity (PA) levels may contribute to low BMD in this population. The objective of the study was to investigate whether PA levels were related to the femoral neck bone mass distribution in a sample of 14 males and 12 females with DS aged 12-18 years. Methods: BMD was evaluated by dual energy X-ray absorptiometry (DXA) at the integral, superolateral and inferomedial femoral neck regions and PA levels were assessed by accelerometry. The BMDs between the sexes and PA groups (below and above the 50th percentile of the total PA) were compared using independent t-tests and analyses of covariance (ANCOVAs) controlling for age, height and body weight. Results: No differences were found between the BMDs of males and females in any femoral neck region (p > 0.05). Females with higher PA levels demonstrated increased integral (0.774 g/cm(2) vs. 0.678 g/cm2) and superolateral femoral neck BMDs (0.696 g/cm2 vs. 0.595 g/cm2) compared to those with lower PA levels (p < 0.05). In males, no differences (p < 0.05) were found in the BMDs between the PA groups. Conclusions: This investigation shows that females accumulating more total PA presented increased BMDs at the integral and superolateral femoral neck regions (14.1% and 17.0%, respectively) when compared to their less active peers. These data highlight the importance of PA in females with DS to counteract their low bone mass and to improve their bone health.