The effects of a 16 week physical activity program on bone mineral density in lean and obese prepubescent children ages 8--11

The current obesity epidemic has become a major health crisis to citizens around the United States. Obesity has been successfully linked to a plethora of different disease states including cardiovascular disease, diabetes, and stroke. Although many people might not recognize the trends, the obesity epidemic is putting children as young as 5 and 6 years of age at a health disadvantage compared to children of a healthier weight. With 17% of American's children being classified as obese, it is important to uncover what detrimental influences obesity has on the childhood body. Specifically, with respect to bone health, there is a good amount of information supporting the concept that there is increased acquisition of bone mineral density (BMD) through exercise in children. However, none of these studies have investigated the effects of physical exercise on BMD in obese children compared to lean children. Previous studies show that overweight and obese children are at an increased risk of bone fracture due to low bone mass and bone area for weight. An increased response in BMD or bone mineral content (BMC) of obese children due to exercise could improve bone strength and decrease fracture risk. The purpose of this study was to investigate whether there were differences in BMD acquisition in lean and obese children in response to a 16-week exercise intervention. Dual energy X-absorptiometry (DEXA) was used to assess the change in BMD in children at week 0 and 16. Participants were grouped by body mass index percentile as obese (n=41) or lean (n=19) and then randomly assigned to exercise or control groups. The exercise protocol consisted of aerobic activities such as running, basketball, tennis, football, etc. Participants were required to meet a heart rate average of >140 beats per minute each one-hour exercise session. The protocol for the study was reviewed and approved by the East Carolina University Institutional Review Board. Both lean and obese exercise groups increased total body bone mineral density (+0.026+/-0.001g/cm 2, +0.028+/-0.001g/cm2 respectively; p<0.05) from week 0 to 16. Total body BMC also increased in the lean and obese (+111+/- 4.4g, +106+/-4.3g respectively; p<0.05) exercise groups. There were no significant increases in BMD in controls groups. The increases in BMD and BMC of the exercise groups, suggests that bone metabolism responded similarly in both treatment groups. The results advocate that there is no difference in bone acquisition of lean and obese prepubescent children of different BMI percentiles.