Background There is limited research on whether physical activity (PA) in early childhood is associated with the timing of pubertal events in girls. Methods We used data collected over 2011–16 from the LEGACY Girls Study (n = 984; primarily aged 6–13 years at study enrolment), a multicentre North American cohort enriched for girls with a breast cancer family history (BCFH), to evaluate if PA is associated with age at thelarche, pubarche and menarche. Maternal-reported questionnaire data measured puberty outcomes, PA in early childhood (ages 3–5 years) and total metabolic equivalents of organized PA in middle childhood (ages 7–9 years). We used interval-censored Weibull parametric survival regression models with age as the time scale and adjusted for sociodemographic factors, and we tested for effect modification by BCFH. We used inverse odds weighting to test for mediation by body mass index-for-age z-score (BMIZ) measured at study enrolment. Results Being highly active vs inactive in early childhood was associated with later thelarche in girls with a BCFH [adjusted hazard ratio (aHR) = 0.39, 95% CI = 0.26–0.59), but not in girls without a BCFH. In all girls, irrespective of BCFH, being in the highest vs lowest quartile of organized PA in middle childhood was associated with later menarche (aHR = 0.70, 95% CI = 0.50–0.97). These associations remained after accounting for potential mediation by BMIZ. Conclusion This study provides new data that PA in early childhood may be associated with later thelarche in girls with a BCFH, also further supporting an overall association between PA in middle childhood and later menarche.

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童年体力活动和青春期时机：LEGACY 女孩研究的结果

背景 关于幼儿期体力活动 (PA) 是否与女孩青春期事件发生时间相关的研究有限。方法 我们使用 LEGACY 女孩研究（n = 984；主要年龄为 6-13 岁）中收集的 2011-16 年数据来评估，该研究是一个多中心的北美队列，主要针对有乳腺癌家族史 (BCFH) 的女孩。 PA 是否与乳房初潮、阴毛初潮和初潮年龄有关。母亲报告的问卷数据测量了青春期结局、儿童早期（3-5 岁）的 PA 和儿童中期（7-9 岁）有组织 PA 的总代谢当量。我们使用区间删失威布尔参数生存回归模型，以年龄为时间尺度，并根据社会人口统计学因素进行调整，并测试了 BCFH 的效果修正。我们使用逆比值加权来测试研究注册时测量的年龄体重指数 z 得分 (BMIZ) 的中介作用。结果 幼儿期高度活跃与不活跃与 BCFH 女孩的乳头发育后期相关[调整后风险比 (aHR) = 0.39，95% CI = 0.26–0.59），但对于没有 BCFH 的女孩则不然。在所有女孩中，无论BCFH如何，在童年中期处于有组织PA的最高和最低四分位数与初潮较晚相关（aHR = 0.70，95% CI = 0.50-0.97）。在考虑了 BMIZ 的潜在中介作用后，这些关联仍然存在。结论 这项研究提供了新的数据，表明儿童早期的 PA 可能与 BCFH 女孩较晚的乳房发育有关，也进一步支持了儿童中期的 PA 与较晚的初潮之间的总体关联。