Objectives: (1) Generate accurate estimates of the relationship between decimal age (i.e., chronological and relative) with swimming performance based on longitudinal data. (2) Determine whether corrective adjustment procedures can remove Relative Age Effects (RAEs) from junior/youth swimming. Design: Longitudinal and repeated years of cross-sectional performance data were examined. Methods: (1) Participants were 553 male 100 m Freestyle swimmers (10-18 years) who participated in>=five annual events between 1999-2017. Growth curve modelling quantified the relationship between age and swimming performance, permitting corrective adjustment calculations. (2) Participants were N = 2141 male 100 m Freestyle swimmers (13-16 years) who swam at state/national events in 2015-2017. Relative age distributions for `All`, `Top 50%`, `25%` and `10%` of swimming times were examined based on raw and correctively adjusted swim times. Chi-square, Cramer`s V and Odds Ratios (OR) determined whether relative age (quartile) inequalities existed according to age-groups, selection level and correctively adjusted swim times. Results: Based on raw swim times, for `All` swimmers RAEs was evident at 13 and 14 years-old and dissipated thereafter. But, RAE effect sizes substantially increased with selection level, with large-medium effects between 13-15 years-old (e.g., 15 years — Top 50% Q1 v Q4 OR = 2.28; Top 10% = 6.02). However, when correctively adjusted swim times were examined, RAEs were predominantly absent across age-group and selection levels. Conclusions: With accurate longitudinal reference data, corrective adjustment procedures effectively removed RAEs from 100 m Freestyle swimming performance, suggesting the potential to improve swimming participation experience and performance evaluation.
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