BACKGROUND: The issues of the age effect (the theory of the age influence) have been shown in sport sciences since the 1980s. The theory of age effect works on the assumption that athletes born in the beginning of a calendar year are, particularly in children's and junior age, more successful than athletes born in the end of the year. This fact has been proved by a number of research studies, mainly in ice hockey, soccer, and tennis but also in other sports. OBJECTIVE: The submitted contribution is aimed at verifying of the age effect in junior tennis. The research objective was to find out the distribution of birth date frequencies in a population of tennis players' in individual months, quarters, and half-years in the observed period 2007-2011 and to check the significance of differences. METHODS: The research was conducted on male tennis players aged 13-14 (N = 239), participants of the World Junior Tennis Finals. From the methodological point of view, it was an intentional selection. The birth dates of individual tennis players were taken from official materials of the ITF, the research data were processed using Microsoft Excel. The personal data were processed with the approval of players and the hosting organization (ITF). RESULTS: Testing of the hypothesis on the significance of differences in the distribution of frequencies between individual quarters (Q1-Q4) has proved statistically relevant differences between Q1 and Q3, Q1 and Q4, Q2 and Q3, and Q2 and Q4; a statistically relevant difference has been also found in the distribution of frequencies between the first and second half of the year. On the basis of the results of the presented research, the age effect in the studied population of junior male tennis players can be regarded as significant. CONCLUSIONS:The results of the analysis of the research data confirm the conclusions of similar studies in other sports and prove that in the population of elite junior players, participants of WJTF 2007-2011, there is a pronounced dominance of players born in the first and second quarters, i.e. in the first half-year. The mentioned conclusions show the necessity of reflecting the age effect in sports practice as it can influence sports performance, especially at the junior level.

The relative age effect (RAE) theory is based on the premise that athletes born in the first months of the calendar year have a significant probability of a higher level of physiological, morphological and psychological abilities compared to later-born athletes. The aim of our study was to verify the influence of the RAE on adult ice hockey players, specifically Ice Hockey World Championships’ (IHWC) participants in the years 2015−2017 (n = 1,200). Based on the chi-squared (χ2) analysis, the influence of the RAE during the 2015−2017 period could not be rejected for all observed players (χ2 = 54.6, p < 0.01, w = 0.21) or for all the players for particular years (2015, 2016, and 2017; p < 0.01). During the monitored period (2015−2017), the RAE could not be rejected for any player’s position (forward, defender, or goaltender). Based on the effect size analysis (Cohen’s w), the strongest RAE was observed among goaltenders (w = 0.31), then forwards (w = 0.24) and finally defenders (w = 0.15). The assessment of player’s positions in particular years showed statistical significance for goaltenders only in 2015 (χ2 = 11.3, p < 0.05). With regard to forwards, significance was confirmed for 2015 (χ2 = 8.5, p < 0.05), 2016 (χ2 = 15.2, p < 0.01) and 2017 (χ2 = 14.3, p < 0.01). Therefore, the presence of the RAE could not be rejected for all these cases. The results of the research show that members of national teams in the years 2015−2017 were players who were chronologically older, which is consistent with the results of other authors addressing the RAE.

The theory of Relative Age Effect (RAE) works on the assumption that athletes born at the beginning of a calendar year are more successful than athletes born in the end of the year. The athletes born early have a significant probability of a higher level of physiological, mor-phological and psychological abilities than later born athletes. Several studies show that the RAE was not found in females or it was significantly lower than in males. The research objective was to find out the influence of RAE in WTA Tour TOP100 female professional tennis players (n=500) in 2014–2018. Cohen’s effect size (ES) w was calculated to assess the level of the influence of RAE. To assess the differences between the observed and the expected relative age quarter distribution, Chi-Square test (ꭕ2) was used. In terms of effect size (ES), a medium influence of RAE has been proven in 2016 and 2017 (w = 0.33, resp. w = 0.30); a small influence has been proven in years 2014, 2015, 2018 and in the whole observed period 2014–2018. Based on statistical analysis, the influence of RAE cannot be rejected in years 2016 (p 0.05). The next step was to assess the influence of RAE on the final WTA ranking in 2014–2018. Players have been divided into four intervals: 1–25, 26–50, 51–75 and 76–100 positions. ES has showed the medium influence of RAE in 76–100 positions (w = 0.34); only small influence of RAE was found in other positions. Statistical analysis showed that the influence of RAE cannot be rejected in 1–25, 26–50 and 76–100 positions (p < 0.05): it can be rejected in 54–75 positions. The results of the research have shown the medium influence of RAE in 2016 and 2017: in the recent years (and in the whole observed period of 2014–2018), the influence of RAE was small. The influence of RAE on the final WTA ranking is also small, except the 76–100 positions.

PURPOSE The issue of the Relative Age Effect (RAE) has been studied in the theory of sports for more than 30 years. Most studies concentrate on team sports, while the area of some individual sports like swimming can be considered still underexplored. METHODS The aim of our study was to verify the RAE in young elite swimmers (n = 198) who participated in Czech Republic U14 Championship (1) in male and female samples (2) according to swimming disciplines and distances (3) and performance (times in individual disciplines) between individual quartiles / semesters of birth. The analysis was performed with the use of adequate statistical (chi-square test, Kruskal-Wallis H test, Mann-Whitney U test) and effect size (effect size w index, eta-square test, effect size r index) tests.RESULTS The results showed a different intensity of RAE sex-differences (male: w = 0.033; female: w = 0.006). In the division by the swimming disciplines and swimming distances, statistically significant values with large effect size were found in males in 50 m freestyle, 200 m individual medley, 100 m butterfly and 200 m butterfly. However, this did not apply for girls. Analysis of differences in performance showed a significant difference between the dependent variables (sex, distance, discipline) by different independent variables of quartile / semester of birth with large effect size only in cases of male 100 m breaststroke and female 200 m individual medley.CONCLUSIONS The issue of RAE should be circulated among the coaches working with youth, athletes, sports organizations, but also parents of athletes in order to avoid the termination of actively spent time or drop-outs.

The issue of Relative Age Effect (RAE) focuses on the causes and consequences of the failure to respect development patterns of individuals in relation to their success, especially in sports. This study aims to determine whether the influence of the RAE can be proven in the Czech youth ice hockey league (U15) (n=744). A Chi-Square test (χ2) has shown that the influence in the whole investigated group cannot be rejected (χ2=25.34, p<0.01, w=0.11). The RAE can be rejected in the group of players (n=78) from the three best teams of the competition (χ2=3.09, p=0.38, w=0.11); the influence of the RAE can also be rejected in players (n=75) from the three worst teams (χ2=0.53, p=0.91, w=0.05). The assessment of RAE on playing positions has shown that the RAE can be rejected (χ2=7.31, p=0.06, w=0.22) in the most productive forwards (n=50) as well as in the least productive forwards (n=50) (χ2=0.48, p=0.92, w=0.06). The RAE is rejected in the group of the most productive defensemen (n=50) (χ2=1.71, p=0.11, w=0.11), and in the group of the least productive defensemen (n=50) (χ2=4.15, p=0.25, w=0.17). The RAE cannot be rejected (χ2=8.88, p=0.03, w=0.35) in the group of best goaltenders (n=24); the RAE is rejected in the group of the worst goaltenders (n=24) (χ2=1.5, p=0.68, w=0.14). Although the results have proven that the RAE cannot be rejected in the entire research group, there is no evidence of its influence (with the exception of the best goaltenders) in individual playing positions.