Sports participation and muscle mass affect sex-related differences in bone mineral density between male and female adolescents: A longitudinal study

ABSTRACT BACKGROUND: Sports participation plays an important role in bone gain during childhood and adolescence. The aim here was to identify sex-related determinants of bone mineral density (BMD) differences between male and female adolescents, with emphasis on the role of sports participation. DESIGN AND SETTING: Longitudinal study conducted in a public university in Presidente Prudente, Brazil. METHODS: The sample comprised 48 adolescents aged 11-17 years, of both sexes, who were matched according to sex, age and sports participation. BMD was the main outcome, while muscle mass, sports participation, calendar age and biological maturation were treated as covariates. Participants were followed up after nine months. RESULTS: At baseline, BMD values were similar between the sexes. However, adjustment for covariates showed that BMD was higher among girls at all sites, with a contribution from lean soft tissue (LST) in the model (partial eta-squared, ES-r = 0.619 in upper limbs; 0.643 in lower limbs; 0.699 in spine; and 0.599 in whole body). Sports participation only explained the upper-limb variance (ES-r = 0.99). At the follow-up, the results resembled the baseline except in the lower limbs (P = 0.109), in which BMD was similar between the groups. BMD gain over time was similar between girls and boys in all segments, and baseline LST affected upper-limb and whole-body BMD accrual (ES-r = 0.396 and 0.107, respectively). CONCLUSION: Whole-body and specific-site BMD differed between baseline and follow-up. However,BMD accrual was similar between the sexes, given that muscle mass constituted the most relevant determinant of the difference between them.

研究背景：体育参与在儿童及青少年时期的骨量积累过程中发挥重要作用。本研究旨在明确男女青少年骨密度（BMD, bone mineral density）差异的性别相关决定因素，重点探讨体育参与的作用。
研究设计与实施地点：本研究为纵向研究，实施于巴西总统普雷西德滕特的一所公立大学。
研究方法：研究样本纳入48名年龄介于11至17岁的男女青少年，按照性别、年龄与体育参与情况进行匹配。以骨密度为主要结局指标，将肌肉量、体育参与、实际年龄及生物学成熟度作为协变量。研究对象在9个月后完成随访。
研究结果：基线阶段，男女两性的骨密度值无显著差异。然而经协变量校正后显示，女孩全身各检测部位的骨密度均更高，该模型中瘦体重（LST, lean soft tissue）的偏Eta平方（ES-r）分别为：上肢0.619、下肢0.643、脊柱0.699、全身0.599。体育参与仅可解释上肢的方差（ES-r=0.99）。随访阶段的结果与基线基本一致，但下肢骨密度在两组间无显著差异（P=0.109）。各部位随时间推移的骨密度积累量在男女间均无显著差异，且基线瘦体重仅影响上肢及全身的骨密度积累（ES-r分别为0.396与0.107）。
研究结论：全身及特定部位的骨密度在基线与随访阶段存在差异。但由于肌肉量是导致两性骨密度差异的最关键决定因素，因此男女的骨密度积累速率并无显著不同。