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：体育运动参与在儿童及青少年时期的骨量积累过程中发挥着重要作用。本研究旨在明确青少年男女骨密度（BMD, bone mineral density）差异的性别相关决定因素，并重点探讨体育运动参与的作用。
研究设计与实施地点：本研究为纵向研究，实施地点位于巴西总统普拉登特（Presidente Prudente）市的一所公立大学。
研究方法：研究样本共纳入48名11~17岁的青少年，涵盖男女两性，所有受试者均按照性别、年龄及体育运动参与情况进行匹配。以骨密度（BMD）为主要结局指标，将肌肉量、体育运动参与情况、实际年龄及生物成熟度作为协变量。对所有受试者进行为期9个月的随访。
研究结果：基线时，男女两性的骨密度（BMD）值无显著差异。但在校正协变量后，女性各检测部位的骨密度（BMD）均高于男性，模型中瘦软组织（LST, lean soft tissue）具有显著贡献（偏η平方值：上肢ES-r=0.619；下肢ES-r=0.643；脊柱ES-r=0.699；全身ES-r=0.599）。体育运动参与仅可解释上肢骨密度的变异量（ES-r=0.99）。随访时的结果与基线基本一致，但下肢骨密度（BMD）组间无显著差异（P=0.109）。各检测部位的骨密度随时间的累积量在男女两性间无显著差异，且基线瘦软组织（LST）会影响上肢及全身骨密度的累积（ES-r分别为0.396和0.107）。
研究结论：基线与随访时的全身及特定部位骨密度（BMD）存在差异。但男女两性的骨密度累积量并无显著差异，这是因为肌肉量是导致两性骨密度差异的最相关决定因素。