Relative age effect and competitive distribution on elite professional male kickboxing athletes

Abstract Objective This study investigated the relative age effect (RAE) in elite male professional kickboxers, assessing differences based on competitive success (belt winners vs. non-winners) and weight categories. Methods Data from 452 male professional kickboxers competing in the Glory organization were analyzed across six weight divisions. Athletes were categorized into birth quarters (Q1–Q4), and observed distributions were compared with expected distributions using chi-square goodness-of-fit tests. Effect sizes were calculated with Cramer’s V. Statistical analyses were performed in SPSS 20.0, with significance set at p < 0.05. Results No statistically significant evidence of RAE was found in the overall sample (χ 2 = 1.430; p = 0.698; V = 0.032), across different weight categories, or among belt-winning athletes (χ 2 = 2.218; p = 0.528; V = 0.179). Birth-quarter distributions did not significantly deviate from expected normative values, indicating a uniform distribution throughout the calendar year. Conclusion RAE does not appear to influence professional kickboxing, regardless of athletes’ competitive success or weight class.