Biological maturation influences selection process in youth elite soccer players

Original article written by Marcelo Massa, Alexandre Moreira, Renato Costa, Marcelo Lima and colleagues.

Background

Maturation refers to structural and functional changes in the body as children progress toward adulthood ^[1,2]. The timing and tempo of maturation can differ significantly, whereby timing defines when maturation occurs, whereas tempo is the rate at which maturation progresses. Youth can be classified as biologically ‘ahead of’ (early maturer), ‘on time’ with (average maturer), or ‘behind’ (late maturer) relative to their chronological age ^[1]. Boys who mature in advance of their peers experience the adolescent growth spurt at an earlier age and tend to outperform their less mature counterparts on tests of strength, power, speed, agility, and endurance ^[3,4]. It is widely acknowledged that these increased physical attributes associated with maturity status play a significant role in the identification of potentially talented athletes and their retention within development pathways.

Relative age is determined by date of birth and the selection cut-off date, and refers to a player’s chronological age within their specific age group. Players born earlier in their selection year (e.g., birth quartile [BQ] one and two) have a greater likelihood of being selected into talent pathways (~38-40% and ~24-30%, respectively) when compared to those born later in the year (BQ3: ~15-21% and BQ4: ~13-16%, respectively) resulting in the phenomenon known as the relative age effect (RAE) (5,6). Relatively older players are often assumed to be biologically more mature and, thus, physically superior in comparison to their relatively younger peers (7). Despite these assumptions, relative age does not necessarily imply more advanced maturity (8), with relative age shown to be weakly correlated with maturity status in young athletes ^[9,10].

What the authors did

Within this study, the authors aimed to identify the influence of maturation and relative age on selection for a Brazilian professional soccer academy. One hundred and forty-three young males were pre-selected to be assessed for selection into a U14 Brazilian soccer academy. Players had their stature and body mass assessed, as well as their date of birth recorded. Using date of birth, players were divided into four groups according to the quartile they were born in. BQ1 was from January to March, BQ2 from April to June, BQ3 from July to September and BQ4 from October to December. Additionally, stages of secondary sex characteristic development were assessed by clinical observation, and the Tanner stage criteria were used to estimate maturity status ^[11]. Finally, a salivary testosterone assessment was conducted for all players.

During the time of testing, players were also subject to specific evaluations by coaches and club staff. After a 2-week period, 100 of the 143 players were dismissed and the remaining 43 players were selected to train in the clubs U14 squad. After ~12 months, the final U14 starting team was then assembled. These cut-offs resulted in three distinct groups for the final analysis, “dismissed” (n = 100), “selected” (n = 34) and “starters” (n = 9). The differences in testosterone, sexual maturity, and anthropometrics between the three groups was then assessed.

What the authors found

The researchers identified that both maturation and relative age seem to influence selection into a professional soccer academy, which is in accordance with previous research. The main findings within the current study were that players from the “starters” group had a higher testosterone concentration compared to the “selected” or “dismissed” groups. While there was no difference in pubic hair development across the groups, a significant difference was observed for gonadal development between players from the “starters” and the “dismissed” groups. ^{a b * #}

The authors also found that all players, regardless of group, showed a higher distribution of being born in BQ1 compared to the reference population, confirming the presence of a RAE. More specifically, a significantly greater percentage of players were born in BQ1 of the “starting” group compared to the “dismissed” The authors also found that all players, regardless of group, showed a higher distribution of being born in BQ1 compared to the reference population, confirming the presence of a RAE. More specifically, a significantly greater percentage of players were born in BQ1 of the “starting” group compared to the “dismissed” and “selected” groups.and “selected” groups.

Limitations

This study is well conducted and adds further evidence to our understanding of maturation and selection into elite squads. However, as with all research, there are certain limitations that the results need to be viewed in-line with. In this regard, the findings were from a single professional soccer academy, and may not be generalised to other academies, across different countries. However, the findings are very similar to what has been published previously from soccer academies all around the world. It would also be interesting to know if the coaches and selectors were blinded to the results from the assessments within this study, as selection happened at the same time as testing. It could be possible that results from the tests influenced coaches and selectors decisions.

What this means for coaches

This study highlights further evidence that selection in youth academies is influenced by maturation and relative age. The study provides further evidence that assessing maturity status in youth is important, as it can have a significant influence on physical performance and therefore team selection. Interestingly, previous research has highlighted that soccer players less advanced in maturation at U14-16 had greater chance of making it as international or professional players at the adult level ^[12]. Therefore, practitioners should be aware that early maturing or players more advanced in maturation may be more influential during academy age groups, but they may have a limited ceiling and late maturing or players less advanced in maturation should not simply be discounted in academy age groups. 

Reviewer’s comments

This study adds more literature to the area of talent identification in youth soccer. It is clear that early maturers and BQ1 players are more likely to be selected for academy age groups, but later maturers often catch up and overtake their earlier maturing counterparts and have an increased chance of success at the adult level. Assessing maturity, therefore, is vitally important and so are introducing strategies to allow players from a range of maturity status’ to succeed, such as bio-banding.^[13] While Tanner staging has been used to determine maturity status in the current study, there are many less invasive ways, such as assessing predicted adult height ^[14] or maturity offset ^[15], which require simple measures of stature and body mass.

Recommended resources

This is another article to highlight the influence of maturity and relative age on selection in youth soccer, and there is now a significant amount of evidence in the literature. The leading researcher in this area is Dr Sean Cumming, and he, along with his PhD students, have explored key strategies that looks at controlling for maturity, including bio-banding. For more information on bio-banding, and more, listen to the podcast with Sean Cumming or visit his Research Gate page. Adam Kelly is another leading researcher exploring the relative age effect in a number of sports, and his research can be read here, and he highlights his recent research on this podcast. Finally, for coaches looking to estimate maturity status with anthropometric measures, Chris Towlson and colleagues have released the following article and resources to be used with boys and girls.