The issue of the Relative Age Effect (RAE) has been long researched, discussed and published both in the academic and coaching community and the number of studies on it in various sports has significantly grown in recent years. The aim of this study was to verify the existence of RAE among Czech male (n = 6552) and female (n = 4131) junior tennis players and to identify possible differences in birthdate effect between male and female players. The research was carried out in players registered in the years 2007–2016 in the U14 age category in Czech Tennis Association (CTA) database; the athletes were divided into three subgroups (‘Ranked’, ‘Top 100’, ‘Top 10’). Research data were analysed by the methods of descriptive and inferential statistics: relative and absolute frequency, chi-square goodness of fit test () and chi-square test of independence () with the use of effect size (ES index w). A declining tendency of frequencies from Q1 to Q4 between male and female junior players was proven in all three subgroups.In the whole period of 2007–2016, a significant and strong RAE was demonstrated only in the ‘Top 10’ male subgroup (RAE was significant and ES was small or trivial in the other two subgroups). Among the female players, RAE was significant in all three subgroups (ES was small or trivial). Gender differences in RAE in favour of male players were significant in ‘Top 100’ and ‘Ranked’ (ES was small or trivial in all three subgroups). In the short and long term, RAE can have significant implications for the sport development of athletes; both coaches and the professional public can therefore be recommended to pay attention to this issue. The impact of RAE in sport, i.e. the uneven distribution of athletes’ birthdates, is more pronounced especially among junior athletes and often significantly affects their sports development and career.
The issue of the phenomenon known as RAE first appeared in research within the educational system. In the field of sports research, it first emerged in the 1980s. The theory of RAE is based on the assump-tion that athletes born in the early months of the year are usually more advanced in both mental and physical fitness. Many studies have confirmed that birthdates of players in sports such as handball, ice hockey or football are distributed asymmetrically in the respective quarters of the year. A high incidence of birthdates has been shown to exist in the first half of the year. The aim of the study was to determine the impact of RAE on Czech tennis players in the age category of 10–12. The investigated sample consisted of players (n = 1 500) who ranked among the top one hundred in the official ranking of the Czech Tennis Association from 2003 to 2017. In order to verify the conformity of the distribution of the frequency of the players’ birthdates in the sample and the frequency of birthdates among the same population (n = 1 506 504) the Chi-Square test (χ2) was used. The results of the study have shown a significant influence of RAE in certain years in the reference age category of 10–12, and in thirteen of the fifteen years surveyed. The overall results in the reference period 2003–2017 have shown that most of the players were born in Q1 (n = 551) and Q2 (n = 442). Therefore, 2/3 of the players (66%) were born in the first half of the year, while only 1/3 (34%) were born in the second half. A longitudinal study of tennis players aged 10–12 showed the influence of RAE both in specific years (with the exception of 2011 and 2014) and in the reference period 2003–2017 taken as a whole. The results of our research correspond to the results of similar studies performed by other authors. Tennis coaches are advised to address the issue of RAE when working with tennis youth and when selecting players to the sports centers, representations, etc.
