In the selection process for future talent, birthdates are a standard criterion for categorizing athletes, and in many cases, athletes are grouped into age groups or even two-year age groups. Although it aims to organize tournaments and training practices more effectively, this strategy overlooks the age and developmental differences inherent in youth (1, 2). In this perspective, the existing literature is well documented, indicating that, within a given age range, children and adolescents who are older and those who are younger can exhibit significant differences in numerous aspects, including physical and psychological maturation (2–5). As a result, the older ones tend to have more performance advantages than their younger counterparts, being more likely to be selected (6, 7), remaining overrepresented at the senior level (4). Therefore, literature has identified this issue as the relative age effect (RAE) phenomenon. Barnsley (8) proposed that when children are grouped solely by age, there can be a difference of up to a year in age among them (for example, children born in January will have an 11-month advantage over those born in December of the same year).

The RAE has been observed in numerous team and individual sports, regardless of the athletes' sex (4, 6, 9). Recent investigations indicate that an athlete's birth can influence their chances of achieving elite status within sports (10), particularly in youth sports, where physical and psychological maturity can differ significantly among children born months apart (1). In addition, the RAE was found in many sports, such as in Olympic athletes (11), alpine skiing (12), track and field (13), basketball, rugby, football, and volleyball (4, 6, 9, 14), and during fitness tests (15). In fact, this phenomenon has been observed in other disciplines beyond human kinetics, such as mathematics, algebra, measurement, geometry, statistics, and probability (16), as well as reading literacy (17). Recent results also suggest that this effect can be observed in elite Paralympic athletes (14).

Despite the growing evidence on the RAE across different performance contexts, fewer studies have addressed how this phenomenon influences broader developmental domains such as motor competence (MC), which is foundational for lifelong engagement in physical activity and sport. This is particularly important in a societal context increasingly affected by sedentary lifestyles and associated declines in youth physical fitness and quality of life. Notwithstanding, there are few investigations in the literature that examine the effects of RAE on MC in youth (18, 19). The literature has consistently demonstrated that MC is associated with higher levels of physical activity, and that children with higher levels also exhibit higher sports participation (20–23). Another interesting fact is that older children tend to present higher MC levels than their younger peers (24). Therefore, a better understanding of how RAE influences MC may help mitigate early dropout from physical activity and sport, thereby promoting healthier developmental trajectories. Nevertheless, a clear gap remains regarding how RAE interacts with different types of sports engagement (team vs. individual) and non-participation, which may differently affect opportunities for motor development and active lifestyles. While it remains relevant to explore how RAE influences MC, scientific evidence suggests that its impact may be better understood when analyzed in conjunction with sports participation and sex.

The purpose of the present investigation was to examine the effect of the RAE on MC scores in children and adolescents engaged in team and individual sports, as well as those not involved in regular sports participation. Specifically, it explores how variations in birth quartiles (Q) influence MC across these groups. Thus, this research aims to provide new insights into talent identification regarding children and adolescents participating in individual and team sports, emphasizing the importance of addressing RAE through age-appropriate interventions to ensure equitable physical and motor development opportunities. Furthermore, we would like to better understand whether the type of sports participation (team vs. individual) could influence the RAE. Our central hypothesis is that participants born earlier in the year will demonstrate superior MC levels compared to their younger peers within the same age cohort due to the cumulative advantages of being relatively older. Additionally, we anticipate differences in MC levels between children and adolescents who participate in sports vs. those who do not.

The descriptive statistics for MC divided by birth quartiles are shown in Table 2. Data is presented controlling for the MC by sex and sports participation. Descriptive statistics revealed that participants in team sports had the highest mean scores in all MC components, followed by those in individual sports. In contrast, non-sport participants consistently showed the lowest scores.

General one-way ANOVA results indicate statistically significant differences between birth quartiles only in the Manipulative and MC domains. In the Manipulative category, a significant difference is observed between Q1 and Q3 (p = 0.02; η² = 0.01). In MC, significant differences are found between Q1 and Q3 (p = 0.03; η² = 0.01) and between Q1 and Q4 (p = 0.04; η² = 0.01). Controlling for data by sex (Figure 1), no statistically significant differences were found in boys' Locomotor (p = 0.87; η² = 0.00), Stability (p = 0.69; η² = 0.00), Manipulative (p = 0.42; η² = 0.01), and MC (p = 0.64; η² = 0.00) (Figure 1a). The same patterns were also found in girls for the Locomotor (p = 0.48; η² = 0.01), Stability (p = 0.66; η² = 0.00), and Manipulative (p = 0.23; η² = 0.01). However, in MC, there is a significant difference between Q1 and Q3 (p = 0.03; η² = 0.01) (Figure 1b), indicating a small but meaningful effect of birth quartile on MC in this category.

The MANCOVA revealed significant main effects of birth quartile, sports participation, and sex on MC (Wilks' Lambda < 0.05, p < 0.01), indicating that these factors influence MC levels. Sports participation had the strongest multivariate effect (Wilks' Lambda = 0.81, F = 27.67, p < 0.01, η² = 0.10), with team sports participants consistently scoring higher in all MC components than individual and non-participants in sports. Sex also had a significant effect (Wilks' Lambda = 0.79, F = 67.15, p < 0.01, η² = 0.21), with boys demonstrating higher scores overall, particularly in Manipulative skills (F = 137.90, p < 0.01, η² = 0.12). However, the sex effect was non-significant for Stability (p = 0.14). Birth quartile had a multivariate significant impact (Wilks' Lambda = 0.95, F = 4.11, p < 0.01, η² = 0.02); however, univariate analyses revealed that its impact was small and inconsistent across MC components. A significant effect was found for the Manipulative component (F = 2.99, p = 0.03, η² = 0.01) but not for the Locomotor (p = 0.53) or the Stability (p = 0.20). The interaction between birth quartile and Sports Participation was significant for the Locomotor component (F = 3.43, p = 0.00, η² = .02) and MC (F = 2.56, p = 0.02, η² = 0.02), suggesting that the effects of birth quartile on MC are influenced by sports participation (Figure 2).

A significant finding was the three-way interaction among birth quartile, sports participation, and Sex (Wilks' Lambda = 0.96, F = 1.79, p = 0.02, η² = 0.01). The interaction effects were significant in the Locomotor component (F = 2.97, p = 0.01, η² = 0.02), Stability (F = 3.08, p = 0.01, η² = 0.02), and Manipulative (F = 2.46, p = 0.02, η² = 0.01), indicating that the relationship between birth quartile and sports participation varies according to sex. While team sports participation benefits both boys and girls, boys tend to score higher in all birth quartiles, particularly in the Manipulative component. In contrast, girls' scores vary more depending on the type of sport. These findings highlight that sports participation plays a significant role in MC development, with team sports showing the most significant positive impact in our sample. While RAE alone has limited influence, its effects become more apparent when considering sports participation and sex differences.

The present study aimed to analyze the impact of the RAE on MC in school-aged children and adolescents, with a specific focus on how variations in birth quartiles and sport type influence their MC. While RAE showed a statistically significant influence on MC, its effect was limited in magnitude. Results showed that participants born in the first half of the year (Q1 and Q2) had significantly higher MC scores than those born between July–September (Q3) and October–December (Q4), although the effect was not large (η² = 0.01), which is in agreement with existing literature (1, 6, 35). For example, in a systematic review, Cobley et al. (1) identified a consistent prevalence of RAEs, albeit with small effect sizes, across 253 independent samples from 14 sports and 16 countries. Morganti et al. (4) found that early-born players (January to March) were significantly overrepresented in youth national teams, particularly in the UEFA U17 European Championship, where teams with stronger RAEs tend to achieve better results. Findings also showed that at the senior level, RAEs persist but weaken, with a relative increase in later-born players (BQ4), suggesting a reversal effect where initially disadvantaged players develop resilience and long-term potential. The author discussed that their results highlight the inefficiency of early selection systems that prioritize short-term success over long-term talent development, calling for systemic reforms in player identification and development strategies. Nevertheless, our results also showed that sports participation, especially in team sports, and sex differences played a much stronger role in MC outcomes.

The most pronounced differences in our general sample were in the Manipulative component, where participants born in Q1 scored significantly higher than those born in Q3. This is consistent with previous research suggesting that Manipulative skills, such as ball control and object manipulation, may be more influenced by relative age advantages due to increased exposure and practice opportunities (24). However, the effect of birth quartile was not significant for the Locomotor or Stability components, suggesting that other factors, such as overall physical activity and other extracurricular activities, may play a greater role in these components.

Another finding is the observation that, overall, MC was significantly different across birth quartiles for girls. At the same time, none of the individual components (i.e., Locomotor, Stability, Manipulative) showed significant differences. One plausible explanation is that although each motor domain shows only a marginal or non-significant effect in isolation, the cumulative small effects across all three domains may have contributed to a significant difference in the overall MC score. This combination effect is particularly relevant when variability is low within each component but consistent across domains, which appears to be the case in this subgroup. In addition, the finding that manipulative skills were significantly higher in Q1 compared to Q3 (36), but not Q4, may be attributed to the variability in sports participation. It is possible that children born in Q4 benefited from compensatory mechanisms, such as increased participation in structured physical activities or higher motivation due to awareness of early disadvantage (37, 38). These mechanisms have been proposed in the literature as potential buffers against RAE in later-born children, referred to as the “underdog hypothesis”. Towlson et al. (10) suggested that children born earlier in the year tend to show more advanced physical and psychological development, which can enhance their sports performance and motor skills. The findings concerning RAE influence in the Stability and Manipulative components are more pronounced than in the Locomotor component, corroborating previous studies that emphasize the sensitivity of specific motor skills to maturity differences (24, 29). The RAE hypothesis also suggests that children and adolescents born earlier in the selection period (e.g., school year) tend to have an advantage in MC because they are older and more physically developed than their younger peers (39). This advantage can also lead to higher participation rates in sports and better MC scores.

Regarding sports participation, our results demonstrated that participants engaged in team sports consistently outperformed both individual sports participants and non-sport participants across all MC components. The MANCOVA results indicated that sports participation had the strongest multivariate effect on MC, indicating the considerable role of organized sport in MC development. These findings reinforce the importance of sports environments in enhancing motor behavior and align with previous investigations emphasizing the benefits of team sports participation (33, 40).

The differences observed between team sports and individual sports suggest that social and environmental factors also play a role in MC development. Team sports participants are involved in more dynamic interactions, requiring athletes to adapt quickly to unpredictable situations, which may contribute to enhanced motor adaptability and coordination. Additionally, the frequent need for teamwork, passing, and defensive positioning in team sports fosters a broader range of movement patterns and cognitive decision-making skills compared to individual sports (41). In contrast, individual sports tend to emphasize self-paced, repetitive movements, which, while beneficial for specific skill development, may not provide the same level of variability and adaptability. This could explain why team sports participants demonstrated higher MC scores across all measured components, as their training environments likely encourage a more holistic development of MC. Despite this, factors other than the type of sport should be analyzed mainly in younger age categories, such as the under-13 category, where relatively older participants show better performance due to early exposure to formal competition (42).

Additionally, previous research has demonstrated that RAE also affects fundamental movement skills in non-sporting contexts (19, 43, 44). For example, children born in the first quarter of the year exhibit higher proficiency in skills like catching and throwing compared to those born later (43) and perform better in MC assessments, including manual dexterity and balance, compared to their peers born in the second semester (45). Children with low MC are less likely to participate in physical activities and sports, further delaying their motor development (44, 46). This creates a cycle where low MC leads to less participation, which prevents improvement in motor skills, supporting Stodden et al. (47) assumptions. Also, children's perception of their MC can influence their willingness to participate in physical activities (48). Over time, children who accurately perceive their motor abilities are more likely to engage in physical activities, which can improve their MC.

Sex differences were also evident, with boys exhibiting significantly higher MC scores overall, particularly in the Manipulative component (F = 137.90, p < 0.01, η² = 0.12), confirming previous findings (24). While sex differences were non-significant for Stability, boys generally performed better in Manipulative and Locomotor tasks. This finding is consistent with prior research indicating that boys tend to develop greater upper-body strength and coordination, which contributes to their superior performance in object control tasks (2, 29, 49). A notable finding was the significant interaction effect between birth quartile, sports participation, and sex (Wilks' Lambda = 0.96, F = 1.79, p = 0.02, η² = 0.01), suggesting that the relationship between RAE and MC varies according to both sport type and sex. While boys consistently demonstrated higher MC scores across all quartiles, girls' performance was more variable, particularly in team sports. This finding highlights the intricate relationship between relative age, sport type, and sex in MC development, underscoring the need for further investigation.

It is essential to consider how the team sport environment may interact with mechanisms that attenuate or amplify the RAE. Team sports often involve frequent exposure to competitive situations, peer comparison, and conditions that may intensify the advantages of relatively older participants (50). However, these same conditions may also foster adaptive mechanisms in relatively younger players. For instance, later-born individuals may develop superior self-regulation, tactical awareness, and psychological resilience, enabling them to remain competitive in team settings where they face maturational disadvantages (37). Our data supports this possibility, as children in team sports, regardless of birth quartile, showed higher MC scores overall, suggesting that the structured and dynamic nature of team sports may create an environment that not only expands RAE-related disparities but also offers pathways for their mitigation through skill-based compensation, role flexibility, and social reinforcement (51). These mechanisms warrant further investigation but provide a meaningful explanation for why team sport participation emerged as the strongest predictor of MC in our study.

Previous investigations corroborate these findings, where both boys and girls born in the first semester of the year tend to have higher MC scores compared to those born in the second semester (45, 52). Age was also identified as a significant covariate for boys but not girls. Studies have shown that older children generally perform better in various motor tasks than their younger peers in the same age group (49, 53). In the case of boys, this can be explained by the motor skills that tend to improve with age due to increased physical and cognitive development (2, 49), becoming a factor that can influence the RAE in older ages. Our results indicate that younger participants (e.g., elementary school students) show significant RAE, but the effect may diminish with age (54). The literature also indicates that older players (Q1 and Q2), born earlier in the year, are overrepresented in sports, suggesting that they are more likely to be selected and participate at higher levels (55). For example, in under-18 girls' volleyball, a higher percentage of medalist athletes were born at the beginning of the year, indicating an advantage for those with earlier birthdates (56).

Contrary to some of the studies mentioned earlier, our results indicate that the RAE alone has a limited impact on MC when additional factors, such as sports participation and sex differences, are not considered. While participants born earlier in the year exhibited slightly higher MC scores, the magnitude of these differences was small, reinforcing that participation in organized physical activities also plays a decisive role in MC development, more so than RAE alone.

Despite our important results, some limitations need to be highlighted. First, this study employs a cross-sectional design, which does not allow us to establish causality between RAE and MC. Although the statistical analysis controls for factors such as age and sex, it does not account for potential confounding variables like socioeconomic status, access to sports facilities, other extracurricular activities, or regional differences. Additionally, it focuses on participants within continental Portugal, which may limit the applicability of the findings to different cultural or geographical contexts. Future research should consider longitudinal designs, diverse populations, age ranges, and mixed-method approaches to address these limitations comprehensively​. Additionally, investigations analyzing RAE during individual and team sports, as well as those examining cross-cultural differences, may help to better understand this phenomenon.

The present investigation highlights the influence of RAE, sports participation, and sex in MC among school-aged children and adolescents. While children born earlier in the year tend to demonstrate higher MC scores, the effect is relatively small and primarily observed in the Manipulative component. Sports participation, particularly in team sports, has a much more pronounced influence on MC development, emphasizing the importance of providing opportunities for all participants to engage in structured physical activities. Schools and sports programs should personalize teaching approaches to account for RAE. Monitoring MC, adjusting assessment criteria, and implementing fair selection processes can help balance advantages among children of different birth quartiles. Ensuring equitable opportunities prevents early dropouts and promotes long-term engagement and motivation in physical activity. Therefore, our results strongly suggest that by adapting practices, educators, coaches, and policymakers can help create environments where children and adolescents succeed, regardless of their birth quartile.