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Updated: Jun 17, 2026

Assessment of Child Anthropometry in a Large Epidemiologic Study
Published on: February 2, 2017
Seasonal and Sex Differences in Children's Body Composition Under In-Term PA Versus Vacation Non-PA Periods: A
Xiang Pan1,2, Yibo Gao1,2, Lupei Jiang1,2
1China Institute of Sport Science, Beijing, China.
Objectives:
To characterize seasonal body composition changes in Chinese schoolchildren, contrasting in-term periods (school-based physical activity [PA] active) with vacations (PA suspended), and to test whether BMI, body fat percentage (BFP), and weight respond uniformly across sex and season.
Methods:
Natural-experiment observational analysis of a school-monitored cohort enriched for elevated baseline adiposity (92.0% overweight or obese, Chinese WS/T 586); the research team was not involved in the school-delivered PA program's design or delivery. We measured 342 children (212 boys, 130 girls; mean age 10.2 y) from two Beijing primary schools at up to 10 time points over 40 months (September 2021-December 2024) by bioelectrical impedance (1178 observations). Three 12-week windows were defined (in-term, winter vacation, summer vacation); paired changes were tested by Wilcoxon tests and era-stratified trajectories by linear mixed-effects models, with GAMM smooths for visualization only.
Results:
Across 268 in-term paired observations, BMI declined 0.42 ± 1.10 kg/m2 (Cohen d = -0.38), an active reversal while the PA program ran. Both vacations produced gains (winter ΔBMI +0.78, summer +0.95 kg/m2). Effect sizes diverged across indicators: summer d(weight) = +1.48 > d(BMI) = +0.71 > d(BFP) = +0.57. Summer BFP rose 2.6-fold more in girls than boys (+2.32 vs. +0.91 pp., p = 0.032).
Conclusions:
Under this in-term/vacation alternation, children's body composition showed marked seasonal directionality, with active reversal in term and gains during vacations. The indicator-specific effect-size divergence and the 2.6-fold female-skewed summer BFP response are consistent with sex-stratified, tissue-specific dynamics aligning with peri-pubertal sexual dimorphism.
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