The Link Between REA, Selection Bias, and Injury in Youth Sports

Selection Bias

Selection bias amplifies the RAE by focusing on immediate performance over long-term potential. Coaches often unconsciously favour athletes displaying maturity-driven traits, such as greater physicality. An example of this can be found in soccer, where height is heavily relied upon with goalkeeper selection⁽³⁾. This approach tends to overlook the developmental challenges that build resilience in younger athletes.

“Mismatches occur when coaches and practitioners place early maturers in high-intensity programs that don’t align with their developmental stage.”

In youth handball and football academies, selectors often choose early-maturing players for their superior physical metrics (see table 1). However, this advantage fades over time, leading to higher dropout rates as physical differences lessen⁽²⁾. Early biases often waste the potential of late maturers⁽³⁾. Coach perceptions, influenced by confirmation bias, further reinforce this trend by ignoring the abilities of less physically mature athletes⁽³⁾.

Mismatches occur when coaches and practitioners place early maturers in high-intensity programs that don’t align with their developmental stage. Talent systems must address these biases, avoiding selections based only on short-term gains⁽³⁾. One practical approach is bio-banding, which groups athletes by maturity rather than age, and its use is growing in some sports⁽⁴⁾. It is important to note that bio-banding should not replace traditional chronological age-group training, but rather complement it with biologically grouped training. This can be achieved by implementing training sessions or drills that group players by maturity level, focusing on specific physical and technical skills.

Differential Skill Development

Biologically older athletes, who benefit from RAE, often lean on their physical advantages (such as greater size, strength, and speed) as a crutch in early development. This reliance can hinder the development of technical and tactical skills, as success in youth competitions often comes easily without the need to master finer motor skills or strategic thinking⁽⁴⁾. Over time, as physical differences even out in later adolescence or adulthood, these athletes may struggle with skill gaps that limit their progress⁽⁴⁾.

On the other hand, late developers must compensate for physical deficits by focusing on technical ability, agility, and creativity. This effort leads to more practice time and a stronger emphasis on skill mastery. For instance, alpine ski racers show that later-born athletes put in significantly more individual and group practice to keep up with peers. Furthermore, late-maturing boys develop superior technical and strategic skills, along with a more adaptable and resilient mindset, to stay competitive⁽⁷⁾.

These paths shape development differently. Early maturers’ dependence on physicality often results in higher dropout rates and less adaptability as their advantages fade⁽⁴⁾. Meanwhile, late developers who persist show enhanced technical skills and resilience, boosting their elite potential. However, late maturers face higher injury risks during peak height velocity phases due to mismatched loads, increasing their chance of overuse injuries⁽⁶⁾. Early maturers, conversely, may develop chronic issues like tendinopathies from intense programs without enough recovery. Early sport specialization, common among early maturing athletes, also raises injury rates⁽⁸⁾. Maturity-aware training can help balance these risks and promote equitable development, supporting progression through club or national ranks.

Table 1: Prevalence of relative age effect in youth academy selections across sports^(1,2,9)

RAE, Selection Bias, and Injury Risk

Relative age effect and selection bias intersect to create complex injury risks. Early born athletes face higher training volumes and competitive pressures from a young age. During pubertal growth spurts, when bodies are still maturing, these mismatched loads significantly raise injury risks⁽⁴⁾. For example, advanced maturity correlates with a higher incidence of overuse injuries, such as stress fractures⁽⁷⁾.

Later-born athletes who overcome selection hurdles face additional challenges when competing against physically superior peers. This competition can lead to compensatory movements that strain their immature musculoskeletal systems. A key factor is the maturation-training load mismatch, which increases the risk of apophyseal injuries, such as Osgood-Schlatter disease⁽⁶⁾. Selection bias worsens this by forming groups of advanced maturers, intensifying competition without sufficient recovery time.

The health effects go beyond immediate injuries. Chronic overload from biased selection can lead to burnout, dropout, and long-term joint degeneration⁽⁸⁾. Practitioners need to ensure that individual programs are tailored to each player’s specific requirements and factor in their biological age to minimize risks⁽⁸⁾. 

Researchers at the Micheli Center for Sports Injury Prevention conducted a study to determine the relationship between relative age and sports injury in 1,997 pediatric athletes aged 5-17. Their findings showed a significant RAE influence on injury patterns (see table 2)⁽⁶⁾. Furthermore, advanced maturity predicts higher injury burdens, with growth spurts being linked to time-loss injuries⁽⁷⁾.

Relative age effect-driven selection exposes athletes to demanding loads during vulnerable growth periods, raising injury risks in soccer(6). In handball, early maturation biases provide physical advantages but also lead to higher dropout rates, with injury risks tied to unbalanced training⁽²⁾.

Table 2: Injury incidence rates by maturity status and age group in youth sports^(6,7)

Practical Implications

To tackle these issues, practitioners should adopt evidence-based strategies (see figure 2). Maturity assessments, such as the Khamis-Roche method, help accurately estimate players’ maturity status. This data guides bio-banding, which reduces training load mismatches and lowers injury risks⁽⁵⁾.

Coaches should closely monitor training loads, especially during growth spurts, using tools like session rating of perceived exertion to prevent overload and injury. Education on RAE and bias is essential, with training programs for scouts focusing on long-term potential rather than short-term gains. For injury prevention, neuromuscular training, such as the FIFA 11+ Kids, boosts strength and stability, reducing injury risks⁽⁸⁾. Flexible selection criteria, including delayed specialization, can also reduce dropout and injury rates⁽⁸⁾.

“Creating inclusive environments not only lowers injuries but also encourages sustained participation…”

Tracking birthdate distributions in teams reveals RAE patterns, enabling fairer opportunities for all athletes. Practitioners can customize rehab protocols based on relative age, targeting strength imbalances in later-born athletes. Creating inclusive environments not only lowers injuries but also encourages sustained participation and enjoyment in sports.

Conclusion

The RAE and selection bias play a major role in shaping youth sports, determining who advances and at what cost. By linking these factors to injury risks, through mismatched training, varying maturation rates, and biased pathways, research offers clear paths for improvement. The contrasting skill development paths add complexity, with early maturers risking long-term adaptability and late maturers facing unique injury challenges. Practitioners must prioritize equitable, maturity-aware systems to protect the health of young athletes and unlock their potential, ensuring talent development remains fair, safe, and effective.

References

1.    Eur J Sport Sci 2024;39(5):401-421.
2.    Eur J Sport Sci 2017;17(3):349-355.
3.    Int J Sports Physiol Perform 2018;13(6):707-715.
4.    Med Sci Sports Exerc 2015;47(6):1283-1290.
5.    Pediatrics 1994;94(4):504-507.
6.    Br J Sports Med 2016;50(15):936-941.
7.    Am J Sports Med 2024;52(4):987-994.
8.    Curr Sports Med Rep 2013;12(6):364-371.
9.    Int J Sports Sci Coach 2010;5(2):227-238.