This study aimed to clarify whether the relative age effects exist among Japan national athletes who participated in the Olympics and World Athletics Championship from 1991 to 2021 by discipline. We obtained 500 athletes' birth month from a website. The following disciplines were classified: short distance (sprints, hurdles, relays: n＝168), middle-to long-distance (middle-distance, long-distance, marathon, walking race: n＝252), jumping (n＝52), throwing (n＝24), and combined (n＝7). Athletes' birth months were divided into four quarters: April–June, July–September, October–December, January–March. Chi-squared goodness of fit test and residual analysis were used to confirm biased distribution of birth month. The proportion of male short-distance athletes who were born between April and June was significantly higher, which may be due to advantage of physique (e.g., height and BMI). On the other hand, the proportion of male jumping athletes who were born between January and March was significantly higher, indicating that discipline transfer in their youth may have an influence on the relative age effect of jumping athletes. In conclusion, the relative age effect was seen among male short-distance and jumping athletes. These results suggest that athletic training systems in Japan have yet to mitigate the advantages caused by the relative age effect because young athletes' disciplines are selected too early, without careful consideration of the relative age effect.
