Evidence for NO anthropomorphic, fitness or performance differences between Birth Quarters in SELECTED groups within junior development environments.

Some sports researchers/administrators use the risk of ‘unintended consequences’ as a reason to not address Relative Age Effects found in junior development environments. They suggest a link between why later born often outperform early born over senior careers and the inherent Birth Quarter imbalances found at junior level. These imbalances, they suggest, are required to sufficiently challenge later born to achieve higher senior success (Reversal of RAE). These so-called ‘Peer Effects’ are part of the ‘Underdog Hypothesis’.

For example this from a 2024 paper ‘While different measures have been suggested to reduce the age bias in youth academies (Mann & van Ginneken, 2017), it is also true that the current age structure presents a challenging environment for relatively younger players. Therefore, a change in these circumstances might impact their ability to develop extraordinary skills.‘  AND ‘A possible explanation for the RRAE might be that players born late in the year may have become highly skilled, because they were selected and maintained in the base categories, although they had physical and maturational disadvantages (Ashworth & Heyndels, 2007; Grossmann & Lames, 2013).’ Biermann et al (2024).

But what evidence exists to show relatively younger players are more challenged in these environments, & if they are physically disadvantaged? 

Listed below are a number of papers that show NO significant differences between Birth Quarters of selected groups, in junior development environments, for anthropomorphic (height, weight, etc), fitness & performance measures.

If later born, within selected pathways, are not smaller, lighter, slower or weaker how can they be physically disadvantaged? Can they also have counter balancing attributes that help them succeed such as being more likely to be early maturers? Are selected players all above a minimum level & relatively homogenous?

EVIDENCE

Relative Age Effect and Yo-Yo IR1 in Youth Soccer (2012)

Deprez, Vaeyens, Coutts, Lenoir, and Philippaerts

606 Belgian soccer players U10–U19

…no significant differences in anthropometric variables and Yo-Yo IR1 performance were found 

between the 4 birth quarters. However, there was a trend for players born in the first quarter being taller and heavier than players born in the fourth quarter. Players born in the last quarter tended to experience their peak in growth earlier, this may have enabled them to compete physically with their relatively older peers. Our results indicated selection procedures which are focused on the formation of strong physical and physiological homogeneous groups. (Abstract)

Relative Age, Biological Maturation and Anaerobic Characteristics in Elite Youth Soccer Players (2013)

D Deprez, AJ Coutts, J Fransen, F Deconinck, M Lenoir, R Vaeyens, R Philippaerts

374 Belgian Soccer players aged 10.6–16.6 years.

Further, MANCOVA revealed no differences in all parameters between the 4 BQ’s, controlled for age and APHV. These results suggest that relatively youngest players can off set the RAE if they enter puberty earlier. (Abstract)

Indeed, many studies in youth sports explain the overrepresentation of players born early in the selection year by their larger anthropometric dimensions and other physical performance advantages, especially in sports where strength, speed and endurance are key factors [ 18 , 23 , 25 ] . In contrast however, the present results showed no statistical differences in anthropometric characteristics and functional capacities between players across all birth quarters. This finding agrees with a study in 332 Japanese youth soccer players (U10-U15) that revealed no differences in height and body mass across the four birth quarters [ 13 ] . Additionally, both Malina et al. [ 19 ] and Carling et al. [ 4 ] found similar results for anthropometric parameters and functional capacities in 39 elite Portuguese soccer players aged 14 years and 160 elite French youth soccer players aged 14–16 years, respectively. Also, Deprez et al. [ 8 ] reported no differences in anthropometric characteristics across the four birth quarters in 606 elite Belgian soccer players aged 9–17 years. The lack of difference between the physical characteristics (aerobic and anaerobic) of the athletes of each birth quarter in these studies most likely reflects the pubertal variation within each of the samples [ 19 ] (Discussion)

The influence of birth quartile, maturation, anthropometry and physical performances on player retention: Observations from an elite football academy (2020)

R Patel et al

355 English footballers from a Cat 1 Academy U11-U21

This study indicates that within a highly selective cohort of young football players, somatic maturity, anthropometric and physical performance characteristics, but not birth quartile, distinguish individuals that are subsequently retained or dropout in an age group dependent manner.

Effect of Birth Month on Physical Fitness of Soccer Players (Under-15) According to Biological Maturity (2014)

I Fragoso,  LM Massuca, J Ferreira

133 U15 Elite Portuguese Soccer Players

In the present study, all of the anthropometric differences related to the 4 birth quarters groups disappeared when the skeletal age effect was statistically controlled, i. e., when the skeletal age effect was statistically removed, the athletes demonstrated a very similar physical robustness. Considering that the minority of athletes were born during the second semester of the year (22.6 %), it may be suggested that almost all of the athletes may have been selected because of their anthropometrical profile, e. g., stature, and that maturing earlier may be fundamental for being drafted, which is consistent with the findings of other authors [5, 29]. Regardless of the division of groups by quarters or semesters, the observed differences may be explained by an athlete’s biological maturity. (Discussion)

Do anthropometric and fitness characteristics vary according to birth date distribution in elite youth academy soccer players? (2009)

C Carling, F le Gall, T Reilly, AM Williams

160 Elite U14 Footballers

These findings suggest that the relative age of the performer may not always be linked to a significant advantage in physical components.

Physical and Anthropometric Characteristics Do Not Differ According to Birth Year Quartile in High-Level Junior Australian Football Players (2021)

P Larkin, CT Woods, J Haycraft, DB Pyne

AFL National Draft Combine (n = 1549; M age = 18.1; SD age = 0.3)

We conclude that the physical and anthropometric profiles of high-level junior Australian Football players were similar according to birth year quartile across the modeled period.

The relative age effect among elite youth competitive swimmers (2012)

AM Costa, MC Marques, H Louro, SS Ferreira, DA Marinho

The best 50 Portuguese swimmers (age 12-18, M/F)

Findings of this study show that a higher number of swimmers, particularly males, are born in the first two quarters of the year, although there is mostly no effect of seasonal birth date on performance differences within the top 50 swimmers. (Abstract)

Relative age effect on anthropometry, biological maturation and performance of young soccer players (2015)

M Matta, AJ Figueiredo, ES Garcia, FZ Wernek, A Seabra

119 Brazilian Soccer Players U15 & U17

These results suggest that there is a higher proportion of young Brazilian soccer born in the first months of the year, but that RAE does not necessarily constitute an advantage under the anthropometric, physical and technical standpoint. (Abstract)

Relative Age Effect: Relationship between Anthropometric and Fitness Skills in Youth Soccer (2015)

A Gioldasis, E Bekris, E Michelinakis, I Gissis

347 Amateur Greek Soccer Players age 9-16

Analyses of variance indicated many significant differences among players of different birth quartiles (from P< .001 to P< .05) for all the skills that were examined. The chi square test that was conducted to assess the distribution of players, showed that for all four different age groups no statistically significant difference was found regarding the birth quartile of players. (Abstract)

So where there is no RAE in populations prior to any selection process there WILL be anthropometric & skill differences.

CONCLUSION

So if there are no physical differences between birth quarters, there are no RAE underdogs & there are no RAE peer effects in junior development environments, unless they are caused by non-physical factors. Though, if ‘selection effects’ can cause no significant differences in physicality, then perhaps they can cause no significant differences for other factors too?

Ashworth & Heyndels (2007) & Bryson, Gomez & Zhang (2017) offer good explanations as to why ‘selection effects’ can cause ‘RAE Reversal’ effects in terms of performance outcomes over senior careers. Peer Effects are not needed to explain this phenomenon. Instead ‘Selection Effects’ are probably at play resulting in relatively more overselected, low quality, early born leaving professional sport, as they age, than underselected, higher quality, later born… a regression to the mean now that RAE is purely residual. Comparing the career performance outputs of the more Relative Age balanced final senior cohorts with the RA imbalanced junior cohorts will show a RRAE.