The Heterogeneous Nature of the Relative Age Effect: The Role of Sport, Developmental Stage, and Selection Context

This systematic review aims to comprehensively examine the reflections of the Relative Age Effect (RAE) on athletic performance, athlete selection, and developmental advantage in child and adolescent athletes within the framework of sport type, developmental stage, and selection context. The study was designed in accordance with the PRISMA 2020 guidelines, and studies published between 2019 and 2025 were systematically reviewed. Following the title and abstract screening, 40 studies were evaluated, and after full-text assessment, 30 studies meeting the inclusion criteria were included in the analysis. The majority of the reviewed studies employed a cross-sectional design and involved athletes aged between 3 and 18 years.The findings indicate that the relative age effect is widely observed in sports contexts; however, the magnitude of the effect varies depending on sport type, age category, level of biological maturation, and the structure of selection systems. In particular, athletes born in the first quarter of the year exhibit higher representation and success rates in team sports requiring high levels of physical contact and strength, as well as in selective developmental stages. Conversely, the effect appears to be more limited in some sports characterised by open participation policies or a greater emphasis on technical skills. It is also observed that RAE is more pronounced in early childhood in terms of motor skills and physical fitness parameters; however, structured intervention programs may mitigate this inequality.In conclusion, the relative age effect is a multidimensional phenomenon that should be considered in athlete selection and development processes. The adoption of biological mat-uration-based approaches, flexible age categories, and multidimensional evaluation systems by sports federations and clubs is of critical importance in reducing potential talent loss.