Associations Of Physical Activity And Bone Health Outcomes Among Underweight Adolescents

Abstract

PURPOSE. To examine the relationship between physical activity (PA) and bone mineral density (BMD) at 5 sites: total body minus head, left leg/arm, lumbar spine, and pelvis among underweight adolescents (BMI < 5th percentile). METHODS. Data from the 2011-2012 National Health and Nutrition Examination Survey (NHANES) were used. Free-living PA was assessed over 7 days using ActiGraph accelerometers, and bone health metrics were measured through dual-energy X-ray absorptiometry (DXA). After selecting the underweight adolescents with both PA and DXA, there remained 47 participants (Age: 15.53 ± 2.71 yr., Male%: 63.83%, Height: 163.64 ± 13.13 cm, Weight: 43.63 ± 9.40 kg, BMI: 16.05 ± 1.35 kg/m2). The PA metric was assessed by Monitor-Independent Movement Summary (MIMS) units per day. Maximal PA MIMS (PA.max), mean PA MIMS (PA.mean), and summed PA MIMS (PA.sum) over 7 days were computed to represent PA dose. The bone health outcomes were the BMD of the total body minus head, left leg/arm, lumbar spine, and pelvis. The partial correlations between PA and bone health metrics controlled by height and weight were computed. RESULTS. Means ± standard deviations of PA.max: 16,735.79 ± 5,333.40, PA.mean: 12,398.54 ± 4,423.51, and PA.sum: 85,131.52 ± 32,148.25. Correlations between different PA metrics and BMDs are summarized below:CONCLUSION. For males, there were low positive correlations between PA.mean/PA.sum and BMDs, but moderate correlations with pelvis BMD; there were low positive correlations between PA.max and left arm/lumbar spine BMD, but moderate correlations with BMDs at the total body minus head, left leg, and pelvis. Some sex differences were noticed, with in general higher correlation in males and some negative correlations in females’ up-body sites. The results indicated the importance of PA on bone development in underweight adolescents, especially for boys, and more studies with large samples on sex differences in certain location are urgently needed.