Birth-quarter distribution, morphological characteristics, and team competitive performance in group rhythmic gymnastics

This study examined birth-quarter patterns across competitive categories in group rhythmic gymnastics, their associations with morphological characteristics, and whether team-level relative-age composition, chronological age, and height were associated with competitive success. The sample comprised 241 female gymnasts from the 2025 Brazilian Group Rhythmic Gymnastics Championship: Pre-Juvenile (n = 68), Youth (n = 51), Junior (n = 62), and Senior (n = 60). Birth dates were classified into quarters (Q1–Q4), and anthropometric measures included body mass, standing and sitting height, leg length, and body mass index. Birth-quarter distributions were compared with population-based expected frequencies derived from Brazilian female live-birth data and weighted by birth year. Morphological associations were tested using generalized estimating equations clustered by club and adjusted for competitive category and decimal age. Exploratory associations with Top-3 success were assessed using conditional logistic regression stratified by competitive event. No category showed a significant departure from the population-based expected birth-quarter distribution after multiplicity adjustment (Holm-adjusted p ≥ 0.251), and the ordinal trend in first-semester representation was nonsignificant (OR = 0.799, 95% CI 0.637–1.000, Holm-adjusted p = 0.251). No morphological outcome remained significantly associated with birth quarter after adjustment for within-club dependence and multiple testing (Holm-adjusted p ≥ 0.083). Exploratory team-level associations with Top-3 placement were nonsignificant and imprecise (Holm-adjusted p = 1.000). Overall, the study found no statistically supported evidence of birth-quarter asymmetry or team-level associations with competitive performance, although imprecision precludes excluding potentially meaningful team-level effects.