Relative age and biological maturity-related selection biases in male youth soccer across different competitive levels within a national association.

OBJECTIVES AND METHODS: This study aimed to examine whether biological maturation and relative age selection biases existed and varied by level of competition (regional, national, and international) in Under-15 soccer players (n = 951) within the Swedish Football Association's male player pathway. A secondary aim was to examine the relationship between relative age and body height, body weight, predicted adult height, percentage of predicted adult height (PAH%), maturity Z-score, and biological age to chronological age offset. RESULTS: The results showed a significant bias (p < 0.001), ranging from trivial-to-small in favour of relatively older players, with the most notable increase between the regional and national levels. There were also significant moderate-to-large biases in favour of early maturing players (p < 0.001), increasing in magnitude with levels of competition. PAH% (p < 0.001) and body weight (p = 0.014) showed the strongest differences across selection levels, where the bias compared to regional level was 0.23 standard deviations (SD) for PAH% at national level and 0.41 SD at international level, while body weight appeared to be particularly related to international team selection (0.36 SD in bias). Relative age showed a moderate positive correlation with PAH% (r = 0.38), but only trivial correlations with all the other biological and physical variables examined (r=-0.05-0.11). CONCLUSIONS: The lack of association between relative age and the estimates of biological maturity timing and the additional physical characteristics suggests that relative age and biological maturity are distinct constructs. We encourage critical examination of how associations select young players for national talent programmes; current practices significantly diminish the chances of selection for those who are late maturing and relatively younger.

Exploring the existence, strength, and independence of relative age and maturation selection biases: a case study in Gaelic football talent development programmes.

BACKGROUND: Biological maturity and relative age player selection biases are well documented in youth sports. However, there has been limited examination of the relationship between these biases. AIM: This study investigated the presence, strength, and independence of relative age and biological maturity selection biases in Gaelic football. SUBJECTS AND METHODS: A total of 247 male players from U14 to U16, from two talent academies were assessed for relative age (decimal age (DA)) and biological maturity (discrepancy between biological and chronological age (BA-CA)). RESULTS: Relative age effects (RAE) were observed in the U14 (DA = 0.62, d = 0.40) and U15 squads (DA = 0.57. d = 0.26) only. A bias towards advanced maturity status was present at U14 (BA-CA = 0.60, d = 0.83), U15 (BA-CA = 0.78, d = 0.89), and U16 (BA-CA, d = 1.01). There was a trivial (U14, r(83) = -0.210; U15, r(88) = 0.060) and low (U16, r(76) = 0.352) correlation between relative age and maturity status. CONCLUSION: Substantial maturity selection biases and, to a lesser degree, relative age biases are evident in youth Gaelic football. Critically, these biases are independent constructs. Coaches and policy makers should be educated on the distinct influences of relative age and maturation, and on strategies to address these biases.

Perceived competence in ice hockey and its associations with relative age, early sport specialization, and players' position.

Introduction: Ice hockey is a sport that has gained much attention in recent times, particularly concerning the development of young players. In the domain of youth sport development, one significant factor that must be considered is the perceived competence of players. This variable is closely linked to positive psychological outcomes and sustained practice. However, there is a lack of understanding about how other important developmental factors such as age, early sport specialization, players' position and relative age affect players' perceived competence. Therefore, the objective of this study is to explore the relationships between these developmental factors, perceived ice hockey competence and a global measure of perceived sport competence. Methods: Data was drawn from 971 players (14.78 ± 1.61 mean age), who completed on-line questionnaires, from which we conducted path analyses involving all variables. Results: Younger players tend to display higher perceived competence scores than older players. Additionally, players who opted to specialize earlier also reported higher perceived competence. Furthermore, forwards and defensemen had differing perceptions of their competence, which was in line with their respective roles on the ice. The study also showed relative age effects, in which players who were born earlier relative to the selection period tend to perceive themselves more advantageously in three components of perceived competence. Discussion: Based on these findings, several recommendations are proposed for coaches and decision-makers to encourage the positive development of ice hockey players. The study highlights that ice hockey-specific competencies are influenced by various factors, such as early sport specialization, relative age effect, player age, and position.

Is There a Relationship Between Birth Quartile and Vertical Jump Performance Among Young Male Elite Volleyball Athletes?

Vertical jump is an important skill that influences volleyball performance. In this study, we analyzed the relationship between vertical jump performance and birth quartile of Brazilian male youth volleyball players. We calculated chi-square goodness-of-fit tests to compare the athletes' birthdate distributions in quarters of their birth years (Q1, Q2, Q3, and Q4) according to player age categories (U17, U18, U19, and U21). We calculated one-way ANOVAs to compare spike jump and block jump heights of players born in different quarters of the same year. Overall, we found a relative age effect (i.e., more players with birth dates early in the birth year) in U17 (p < .001), U18 (p < .001), U19 (p < .001), and U21 (p = .04). Regarding vertical jump performance, U18 athletes born in Q2 reached higher spike jump heights (p = .006) and block jump heights (p = .002) than athletes born in Q4, and U19 athletes born in Q1 reached higher block jump heights than athletes born in Q3 (p = .049). There were no significant differences in vertical jump performance across birth quartiles among U17 and U21 athletes. Thus, a relative age effect was present in all age categories but not always reflected in vertical jump performance. Volleyball coaches and policymakers are still advised to employ strategies to ensure fairer opportunities for players born later in the year of their eligibility dates, as we found RAE to be sometimes, but not always, related to higher spike or block jump heights even among these older adolescents and young adult athletes.

The impact of relative age effects on psychosocial development: A systematic review.

BACKGROUND: Within the same school class, it is usual to find children who differ in age by almost a full calendar year. Although associations between being relatively young and poor academic outcomes are well documented, and relatively consistent, the associations between being relatively young and psychosocial outcomes are less clearly documented. AIMS: To review research which presents data relating to associations between a child's relative age and their psychosocial development. METHODS: A systematic review was conducted and reported in accordance with PRISMA guidelines. RESULTS: Fifty-nine papers met the inclusion criteria. The outcomes of the narrative synthesis and three meta-analyses found consistent, but very small, associations with relative age indicating that those who are relatively young are more likely to have more negative behaviour, mental well-being, and social experiences. CONCLUSIONS: Although being relatively young is associated with more negative psychosocial outcomes, the magnitude of these associations is consistently small. Furthermore, many of the outcome measures used are likely to be the result of multiple influences, not limited to the effects of relative age. Therefore, the findings are reassuring as they suggest that relative age itself is unlikely to substantially increase an individual's risk of poor psychosocial development.

Are Late-Born Young Soccer Players Less Mature Than Their Early-Born Peers, Although No Differences in Physical and Technical Performance Are Evident?

The aim of the study was to compare the status of somatic maturity, anthropometry, strength, speed, and soccer-specific technical skills of players from leading youth soccer academies born in different quarters of the same calendar year. A total of 678 young male soccer players from eight leading Russian soccer academies took part in the study. The following anthropometric measures and physical characteristics were measured: height, weight, body mass index, countermovement jumps (CMJ), 5, 10, and 20 m sprints, speed dribbling, foot and body ball juggling, and short and long pass accuracy. The determination of somatic maturity as a percentage of projected adult height was collected. All subject dates of birth were divided into four quartiles according to the month of birth. The analysis of all data obtained was conducted both within the total sample and by quartiles of birth, according to the age group categories of 12-13 years, 14-15 years, and 16-17 years and the degree of somatic maturity. There was a widespread relative age effect, with 43.5% of early-born players and only 9.6% of late-born players representing the sample. Early-born players were more mature than late-born players (p < 0.001 and p < 0.001) but had no statistically significant differences in strength, speed, or soccer-specific skills.

Relative Age Effects and Self-Organized Sport Practices Among Adults.

Purpose: Given that previous research on relative age effects (RAEs) has only focused on organized sport, the aim of this exploratory study was to examine whether this phenomenon also existed among self-organized practitioners. In relation to that, a second aim was to know whether self-organized sport practices could be favored by late-born practitioners as a result of a strategic adaptation. Method(s): Representative sub-samples of 474 soccer players, 363 basketball players, 2,536 swimmers, 1,788 strength training practitioners, 1,873 pétanque players, 973 table tennis players and 2,136 runners were analyzed. Results: The results did not show any significant RAEs, including in sport practices that are sensitive to this phenomenon such as soccer or basketball. The results did not show any significant overrepresentation of late-born people either. Conclusion: This study suggests that self-organized sport practices are not impacted by the RAEs. This finding is interesting because self-organized sport practice is the most important one in numbers.

The birthplace and relative age effects in Brazilian olympic athletes: a cross-national comparison.

Purpose: Our purpose was to verify the existence of birthplace and relative age effect (RAE), as well as the association between birthplace effect and RAE among Brazilian athletes competing in the Olympic Games. Methods: Data included information about Brazilian Summer Olympic athletes from 1920 to 2021. To investigate RAE, athletes' birthdate was distributed into birth quartiles (Q1: Jan-Mar; Q2: Apr-Jun; Q3: Jul-Sep; Q4: Oct-Dec), while birthplace effect was assessed considering the state and the region (Southeast; Northeast; South; North; and Midwest) of birth. The Chi-square test (χ2) was used to verify differences between the birthplace effect and RAE. Results: The sample consisted of 388 Brazilian athletes of both sexes, distributed in 38 sports modalities from 23 Brazilian states (Southeast = 66.5%; South = 14.4%; Northeast = 12.1%; North = 1.5%; Midwest = 5.4%). For both sexes, most of the athletes were from the São Paulo state (37.4%), followed by Rio de Janeiro (18.3%), both from the Southeast region. For birthdate distribution according to birthplace, it was observed that the North region presented the highest frequency of athletes born in Q1 (50%), followed by the Northeast and Southeast regions. No significant differences were found for the birthplace effect (χ2 = 5.69, value of p = 0.128) and RAE between sexes (χ2 = 0.530, value of p = 0.912), nor was shown an association between the birthplace effect and RAE. Conclusion: Most Brazilian Olympic athletes are from the Southeast region, but no RAE was established regarding their birthplace. Results from the present study can guide sports public policies in Brazilian regions, especially in the Midwest, North, and Northeast regions, which are underrepresented in Brazilian high-performance sports.

The Relative Age Effect in Ice Hockey: Analysis of Its Presence, Its Fading and of a Reversal Effect among Junior and Professional Leagues.

This study analyzes the relative age effect (RAE) among the world's best junior hockey leagues and in the NHL. Despite the prevalence of RAE in ice hockey, past research suggests its fading-reversal over time, which may occur at later stages of athletic development. The hypothesis of the RAE reversal was tested with two sources of raw data files from the 2021-2022 season: 15 of the best international junior and minor professional leagues (N = 7 399) and the NHL (N = 812). Birth quartile distributions were analyzed to verify the prevalence of RAE and quantile regression was used to test the reversal of RAE hypotheses. Advanced hockey metrics were aggregated from multiple data sources and used to compare early born with late born players using birth quartiles. Prevalence of the RAE was verified with crosstabs analyses and quantile regression was used to test the reversal effect. Results indicated that the RAE still prevailed in ice hockey, with higher magnitude in Canadian leagues. Regression analyses showed that late-born junior and minor pro players, despite getting less exposure in terms of games played, attained levels of offensive production similar to those of early born players. Late-born players able to emerge in the NHL performed similarly and sometimes displayed better performance (in some markers). Results suggest that stakeholders should find ways to pay special attention to late born players in talent identification processes and offer them opportunities to develop at the highest levels.

Relación entre el efecto relativo de la edad en el campeonato de España de golf en categorías Sub16 y el rendimiento deportivo / Relação entre o efeito relativo da idade no campeonato espanhol de golfeU16 e o desempenho desportivo / Relationship between the relative effect of age in the Spanish U16 golf championship and sporting performance

En la presente investigación se plantearon dos objetivos: 1) identificar la proporción de jugadores de golf en edad de formación que se clasificaban para los campeonatos de España en función del año y del trimestre del año de nacimiento tanto para el total de la muestra, como para la muestra dividida por sexos. 2) Analizar el efecto de la edad relativa sobre el rendimiento de los jugadores y las jugadoras de golf en el campeonato de España en las diferentes categorías para el total de la muestra, como para la muestra dividida por sexos. Se incluyeron un total de 794 jugadores de golf, (511 varones, media de edad: 13,91±2,08 años; y 283 mujeres, media de edad: 14,29±1,89 años). De cada participante se obtuvo la siguiente información: año de nacimiento, mes de nacimiento, inscripción y participación en el Campeonato de España de golf, posición obtenida en el campeonato. Se observaron diferencias significativas en cuanto a la asistencia al Campeonato de España en función del año de nacimiento (χ2=22,92; p=0,001) y en función del cuartil de nacimiento (χ2=57,59; p=0,001) al analizar el conjunto de los participantes. El análisis de regresión mostró que el puesto en el Campeonato de España puede ser un factor predicho por el año de nacimiento en un porcentaje entre el 7 % y el 15% de los casos (p<0,001-0,009). En base a estos resultados, sería necesario replantear el sistema de competición de los campeonatos nacionales de golf en edades en formación para garantizar una competición en igualdad de condiciones. (AU)

The present study had two objectives: 1) to identify the proportion of junior golfers qualifying for the Spanish Championships as a function of year and quarter ofthe year of birth for the total sample, as well as for the sample divided by sexes. 2) To analyse the effect of relative age on the performance of golf players at the Spanish Championships in the different categories for the total sample, as well as for the sample divided by sexes. A total of 794 golf players were included (511 males, mean age: 13.91±2.08 years; and 283 females, mean age: 14.29±1.89 years). The following information was obtained for each participant: year of birth, month of birth, participation in the Spanish Golf Championship, position obtained in the championship. Significant differences in attendance at the Spanish Championship were observed according to year of birth (χ2=22.92; p=0.001) and according to quartile of birth (χ2=57.59; p=0.001) when analysing the participants as a whole. The regression analysis showed that the place in the Spanish Championships can be a predictorof year of birth in a percentage between 7 % and 15 % of the cases (p<0.001-0.009). Based on these results, it would be necessary to rethink the competition system of the national golf championships to ensure a level playing field. (AU)

A presente investigação tinha dois objectivos: 1) identificar a proporção de jovens golfistas qualificados para o Campeonato de Espanha em função do ano e do trimestre do ano de nascimento para a amostra total, bem como para a amostra dividida por sexo. 2) Analisar o efeito da idade relativa no desempenho dos jogadores de golfe nos campeonatos espanhóis nas diferentes categorias para a amostra total, bem como para a amostra dividida por sexo. Foi incluído um total de 794 jogadores de golfe (511 homens, idade média: 13,91±2,08 anos; e 283 mulheres, idade média: 14,29±1,89 anos). Foram obtidas as seguintes informações para cada participante: ano de nascimento, mês de nascimento,inscrição e participação no Campeonato Espanhol de Golfe, posição obtida no campeonato. Foram observadas diferenças significativas naparticipação no Campeonato de Espanha de acordo com o ano de nascimento (χ2=22,92; p=0,001) e de acordo com o quartil de nascimento (χ2=57,59; p=0,001) ao analisar os participantes como um todo. A análise de regressão mostrou que o lugar no Campeonato de Espanha pode ser um preditor do ano de nascimento numa percentagem entre 7% e 15% dos casos (p<0,001-0,009). Com base nestes resultados, seria necessário repensar o sistema de competição dos campeonatos nacionais de golfe em júnior para assegurar um campo de jogo nivelado. (AU)

Efecto edad relativa en el baloncesto brasileño a lo largo del tiempo / Relative age effect on brazilian basketball over time

El objetivo de este estudio fue analizar el efecto edad relativa en el baloncesto brasileño durante un período de 15 años mediante la investigación de posibles variables intervinientes. Se analizaron 10856 registros de deportistas de los campeonatos de selección estatales U15, U17, U22 y la liga profesional de 2004 a 2018. Se analizaron la fecha de nacimiento, la altura, la posición en el juego, la región geográfica y el rendimiento del equipo. El efecto edad relativa está presente desde el nivel U15 hasta el nivel de alto rendimiento. Se observó que el efecto edad relativa difiere según la región y la posición del juego. Para concluir, el efecto de la edad relativa es un fenómeno evidente en el baloncesto brasileño desde la Sub15 hasta la liga profesional. Varía según la región geográfica del equipo y la posición del jugador. Esta tendencia se ha perpetuado a lo largo de los años. (AU)

The aim of this study was to analyses the relative age effect in Brazilian basketball over a 15-year period by investigating possible intervening variables. 10,856 records of athletes from youth selection championships U15, U17, U22 and the professional league from 2004 to 2018 were analysed. The birth date, height, game position, geographic region, and team performance were analysed. We observed that the relative age effect is present from the U15 to the high-performance level. It was observed that relative age effect differs depending on region and game position. To conclude the RAE is an evident phenomenon in Brazilian basketball from the U15 up to the professional league. It varies according to the geographic region of the team and the player position. This trend has perpetuated over the years. (AU)

Why age categories in youth sport should be eliminated: Insights from performance development of youth female long jumpers.

Long-term sports participation and performance development are major issues in popular sports and talent development programs. This study aimed to provide longitudinal trends in youth female long jump performance development, participation, and relative age effects (RAEs), as longitudinal data for female athletes are missing. 51'894 season's best results of female long jump athletes (n = 16'189) were acquired from the Swiss Athletics online database and analyzed within a range of 6-22 years of age. To examine longitudinal performance development and RAEs, data from athletes who participated in at least three seasons were selected (n = 41'253) and analyzed. Performance development was analyzed using age groups (AGs) and exact chronological age (CA) at competition. Differences between performances of birth quarters were analyzed using 83% confidence intervals (CIs) and smallest worthwhile change. Odds ratios (ORs) with 95% CI were used to quantify RAEs. With the traditional classification into age groups (AG), performances of athletes born between January and March (Q1) were significantly better than those born between October and December (Q4) from U8 to U17. Using exact CA resulted in similar performances in Q1 and Q4 until the U20 age category. The peak of participation was reached in the U12 category, and then decreased until the U23 category with a substantial drop at U17. Significant RAEs were observed from U8 to U19 and at U22. RAEs continuously decreased from U8 (large effect) to U14 (small effect). The present results show that differences in performance arise from the comparison of athletes in AGs. Thus, going beyond AGs and using exact CA, Q4 athletes could benefit from a realistic performance comparison, which promotes fair performance evaluation, un-biased talent development, realistic feedback, and long-term participation.

Age and Maturation Matter in Youth Elite Soccer, but Depending on Competitive Level and Gender.

This study aimed to explore the relevance of the relative age effect (RAE), maturity status and anthropometry, and their influence on coaches' assessment of players' performance, analyzing both genders and different types of academies (elite vs. non-elite). The sample included 603 soccer players (385 male), from the under 12 (U12), under 14 (U14) and under 16 (U16) categories, belonging to elite and nonelite teams. Coaches' assessment of players' performance, chronological age, anthropometric characteristics, maturity offset (MO) and peak height velocity (PHV) were registered. Our results showed that RAE was present in both genders within the elite, but not in the nonelite academies. Early maturity players were overrepresented in the male elite, but not in the female academies. No relationship was found between RAE and anthropometry in male elite academies. Male elite players showed better anthropometric characteristics than nonelite players, while this pattern of results was not found for female players. The coaches' assessment on players' current performance was not influenced by the chronological age nor anthropometry, but it was linked to the PHV. Coaches from nonelite academies rated better in current assessment of performance the taller players. Our findings suggest that maturity status and RAE play an independent and important role in the talent selection process.

Influência do efeito da idade relativa no futsal masculino escolar de Mato Grosso: análise de acordo com a categoria / Influence of the relative age effect on male school futsal in Mato Grosso: a category-based analysis / Influencia del efecto de la edad relativa en el fútbol sala escolar masculino de Mato Grosso: análisis de acuerdo con la categoría

O objetivo deste estudo foi analisar a existência e a influência do Efeito da Idade Relativa (EIR) em estudantes-atletas de futsal masculino de Mato Grosso de acordo com a categoria etária. A amostra foi composta por 486 estudantes-atletas masculinos de futsal de Mato Grosso das categorias A (15 a 17 anos) e B (12 a 14 anos) que disputaram os Jogos Escolares Mato-grossenses e os Jogos Estudantis de Seleções Mato-Grossenses de 2021. Para análise, foram realizados testes qui-quadrado (χ2) de aderência. Os resultados mostraram a presença do EIR na análise geral e nas categorias A e B, com maior representação de atletas nascidos no primeiro trimestre do ano. Conclui-se que o EIR é um fenômeno presente em estudantes-atletas de futsal masculino do estado de Mato Grosso.

The objective of this study was to analyze the existence and influence of the Relative Age Effect (RAE) in male Mato Grosso's futsal student-athletes according to age category. The sample consisted of 486 male futsal student-athletes from Mato Grosso, in categories A (15 to 17 years old) and B (12 to 14 years old) who competed in the 2021 Mato Grosso School Games and the Mato Grosso Student Selections Games. For analysis, chi-square (χ2) goodness of fit tests were performed. Results showed the presence of RAE in the overall analysis and in categories A and B, with a greater representation of athletes born in the first quarter of the year. It is concluded that RAE is a phenomenon present in male futsal student-athletes in the state of Mato Grosso.

El objetivo de este estudio fue analizar la existencia e influencia del Efecto de la Edad Relativa (EER) en estudiantes-atletas de fútbol sala masculino de Mato Grosso de acuerdo con la categoría de edad. La muestra estuvo compuesta por 486 estudiantes-atletas masculinos de fútbol sala de Mato Grosso de las categorías A (15 a 17 años) y B (12 a 14 años) que compitieron en los Juegos Escolares de Mato Grosso y los Juegos Estudiantiles de Selecciones de Mato-Grosso (Brasil) de 2021. Para el análisis, se realizaron pruebas estadísticas de ajuste chi-cuadrado (χ2). Los resultados mostraron la presencia del EER en el análisis general y en las categorías A y B, con una mayor representación de atletas nacidos en el primer trimestre del año. Se concluye que el EER es un fenómeno presente en estudiantes-atletas de fútbol sala masculino del estado de Mato Grosso.

Push and Pull Factors: Contextualising Biological Maturation and Relative Age in Talent Development Systems.

In this conceptual paper, we contextualise ongoing attempts to manage challenge dynamics in talent systems in sport. Firstly, we review the broad literature base related to biological maturation, relative age, and the proposed interventions to mitigate effects. We suggest that the relative age effect may be a population level effect, indicative of deeper phenomena, rather than having a direct effect on challenge levels. In contrast, we suggest that biological maturation has a direct effect on challenge at the individual level. Therefore, our main critique of many existing approaches to the management of challenge is a lack of individual nuance and flexibility. We suggest the necessity for talent systems to adopt a more holistic approach, conceptualising biological maturation and relative age within a broader field of "push and pull factors" that impact challenge dynamics in talent development in sport. Finally, we provide practical guidance for talent systems in their approach to relative age and biological maturation, recognising that there is no "gold standard". Instead, there is a need to recognize the highly individual and contextual nature of these concepts, focusing on strategic coherence through talent systems for the management of selection and development processes.

Relative age effects and the youth-to-senior transition in Italian soccer: the underdog hypothesis versus knock-on effects of relative age.

Relative Age Effects (RAEs) appear largely throughout youth soccer. However, little is known about how RAEs at youth levels can impact transition at senior levels. Accordingly, this study aimed to: (a) provide further test of RAEs by exploring the birth quarter (BQ) distribution of 2,030 Italian players born from 1975 to 2001 who have played in any of the Youth National Italian Soccer Teams; and (b) investigate how RAEs influence future career outcomes, by exploring the BQ distribution of players who completed the transition from youth squads to the Senior National Team (n = 182). Chi-square statistics revealed significantly skewed BQ distributions for all Youth squads (P values <0.0001), and for the cohort of players who completed the transition (P = 0.003). In contrast, results from the Odds Ratios highlighted how BQ4s were more likely to transition from youth-to-senior compared to BQ1s. Results showed BQ1s remained overrepresented at senior level due to a residual bias effect. Whereas BQ4s who were able to overcome selection processes at youth levels recorded the highest likelihood of competing at senior levels. Involving players' career trajectories in RAEs studies is needed to understand how RAEs impacts career outcomes of early selected players.

From Junior to Elite in Soccer: Exploring the Relative Age Effect and Talent Selection in Spanish Youth National Teams.

The implications of relative age grouping in sport are known as the Relative Age Effect (RAE). This study has the twofold purpose of analyzing RAE in Spanish youth national soccer teams and examining the prediction value of being selected for national youth teams to be a professional. The sample was composed of 548 players divided into five groups. A descriptive analysis of distribution and participation, frequencies, mean and standard deviation, crosstabs, Sankey charts, coefficient correlation and Cohen's effect size criteria and two regression analyses were performed. Results established that the RAE is present in U'17 to U'21 Spanish youth national teams. Talent detection and selection programs are more reliable the closer they are to adulthood, reaching a success rate of almost 100% at the U'21 stage. The selection of players for such programs should be delayed as much as possible, thus, preventing younger players from dropping out and those selected from thinking they have already reached their goal. To this end, they should focus on long-term improvement, not short-term performance. In addition, factors such as the RAE or the maturity level of the athletes should be monitored.

Neighborhood-level socioeconomic factors moderate the association between physical activity and relative age effect: a cross-sectional survey study with Japanese adolescents.

BACKGROUND: Relative age effect is defined as a phenomenon where children born early generally perform better than children born later in the same cohort. Physical activity is an important factor that might be influenced by the relative age effect. Socioeconomic factors (e.g., parent's income, education level) are also associated with the adolescent's physical activity. However, no existing study has examined whether socioeconomic factors moderate the relative age effect on the adolescent's physical activity. This study aims to clarify whether and how birth month and socioeconomic factors relate to organized sports and physical activity among adolescents in Japan. METHODS: We conducted a questionnaire survey targeting 21,491 adolescents who live in a widespread neighborhood. We included 8102 adolescents (4087 males and 4015 females: mean age 13.1 ± 1.4) in the analysis. Based on the participants' birth months, we divided them into four groups (April to June, July to September, October to December, January to March). We asked participants to report their organized sports participation. Using the International Physical Activity Questionnaire for Japanese Early Adolescents, we identified their moderate to vigorous physical activity (MVPA). Neighborhood-level socioeconomic factors (areal deprivation, average annual income, education level) were analyzed based on national surveys, such as the population census. We performed multilevel logistic and linear regression analysis for organized sports participation and MVPA, respectively. Moreover, a simple slope analysis was implemented if the interaction between birth month and socioeconomic factor was significant in the multilevel linear regression analysis. RESULTS: Among males, relatively younger adolescents (adolescents who were born later in the same grade) were less likely to participate in organized sports activites (OR=0.90, 95% CI 0.82-0.97, p<0.05), while both males and females engaged in less MVPA (b=-0.54, b=-0.25, p< 0.01, respectively). We observed an interaction between birth month and socioeconomic factors. Among males in low-income neighborhoods, and females in more deprived neighborhoods, relatively younger adolescents engaged in less MVPA. CONCLUSIONS: Socioeconomic factors moderate the relative age effect on adolescents' physical activity. The relative age effect on adolescents' physical activity might be more likely to appear among adolescents from socioeconomically disadvantaged neighborhoods.