Relative age effect and age of peak performance: an analysis of women's football players in the Olympic games (1996-2016)

Abstract

Aim:

The purpose of this study was to investigate the relative age effect and the age of peak performance of women's football players who participated in the Olympic Games from 1996 to 2016.

Methods:

Birth dates, playing positions, and nationality of all players registered in women's football competition in the Olympic Games (1996 to 2016) were collected. All data used in this study were obtained from the official website of the Federation Internationale de Football Association (www.fifa.com). The sample size of the study comprised 1,203 players.

Results:

We found an average age of 25.1 ± 4.0 years old and a significant increase of 1.4 years in the average age from 1996 (25.0 ± 3.9 years old) to 2016 (26.4 ± 3.7 years old) (p < 0.001). The comparison of the players’ age between playing positions reveals that the goalkeepers are the oldest players (26.2 ± 4.4 years) and the forwards are the youngest players (24.4 ± 3.8 years) (p < 0.001). The RAE for women's football players showed neither effect over the years nor in different playing positions.

Conclusion:

We found an aging trend in women's football in the past two decades and different ages of peak performance among the playing positions. The current findings provide valuable information to coaches and professionals to program long-term training and to promote athletes’ progression towards their performance targets.

Keywords
elite sport; development; athlete selection; maturation; women's sport

Introduction

In elite sport, the path to excellence is a complex process being affected by direct (e.g. genes, training, and psychological characteristics) and indirect (e.g. social-cultural aspects, familial support, and instructional resources) factors¹. Age has a dual role in this process acting as a direct factor and influencing indirect aspects of sports systems. On the one hand, chronological age, maturation, and growth are individual characteristics that influence the athlete's development. On the other hand, the age groups and the talent selection and judgment processes are human constructions that play an important role in maintaining and developing practitioners in the sport. This understanding led to two research topics related to the aging process in sport, the age of peak performance (APP) and the relative age effect (RAE). The former investigates the relationship between age and maximum sports performance, while studies on RAE investigate the influence of age, growth, and maturation on the selection, training, and development of the athletes. Both areas provide valuable information to coaches and scientists regarding the individual development of the athlete as well as the social-cultural influence on his/her formation.

The age of peak performance has been mainly investigated in athletics showing different characteristics between male and female athletes^{2 -5}. For instance, Lara et al.⁵ showed that the best women's performance was obtained at 29 years and in men and at 27 years. Nikolaidis et al.⁴ has also shown that women were older than the men in the 10-km, half-marathon, and marathon events. These results are important to analyze athletes’ longitudinal performance and to program long-term training aiming to obtain maximal performance at specifics ages. However, the analysis of peak performance in team sports is more recent and mainly focused on male athletes. In football, Kalén et al.⁶ have recently shown that the average age of men's players increased from 24.9 to 26.5 years over the last decades and suggested that factors like the increased investments of football clubs, increased support and facilities, and the greater monitoring led to an extended sports career. We found only one study on women's football showing the average peak age between 21-29 years of age based on the athletes at the London 2012 Olympic Games⁷. Although this cross-sectional study provided a picture of APP in women's football, the aging patterns in the past decades are still unknown. Furthermore, there is evidence that the physiological demands of football vary in different positional roles⁸ indicating that the age of peak performance may also be different according to the tactical positions.

In international football, age becomes also an important indirect factor in athlete's development as players are organized in categories based on their chronological age aiming to promote fair and competitive competitions⁹. Most classification by chronological age uses a set cutoff date comprising one or two calendar years per cohort^{10 -12}. Although the classification is proposed to balance competition level, this division leads to an age difference of up to 11 or 23 months between the youngest and oldest athlete in the same category and the selection bias of athletes born in the early months of the years, known as relative age effect^{13 -15}. Based on the advanced growth and maturation and, consequently, on the physical, psychological, and cognitive advantage of the players, athletes, born in the early months of the years, have greater access to coaching and training, and more opportunities to develop in sport¹⁶. By contrast, relatively younger athletes may not receive adequate support, possibilities of practice, and play at lower competitive levels¹⁷, which may reflect in higher ratios of drop out¹⁸.

After decades of studies on RAEs in men's football and the knowledge of its negative consequences for the athlete's development, no change in RAEs was found over the past 10 years¹⁰. The great demand for the sport and the search for immediate results sustain the player selection bias in football. By contrast, cultural constraints have historically distanced women from sports and led to lower rates of sports participation. The gender constructions and differences in the opportunities of practice led to a different process of promoting and detecting talents. It is known that the influence of RAE on women's sports is smaller (in certain cases nonexistent) compared to male counterparts^{19 -21}. On the one hand, it can represent an alarming scenario reflecting the gender barriers that still prevent women from practicing sports. On the other hand, the lack of RAE can represent a structured system for sports development that provides fair development for many women's practitioners.

Studies on women's football showed no RAE in French²² and Swiss players¹⁷, while a broader analysis showed the lack of RAE in women's football players participating at Rio 2016 Olympic Games²³. Still, significant RAEs were found in defenders and goalkeepers in Swiss national team¹⁷, Spanish regional teams²⁴, and in different national teams from Europe and North and Central America in under-17 Women's FIFA World Cup²⁵. The results indicate that coaches may tend to select relatively older athletes for goalkeepers and defenders looking for more mature and taller players²⁵. These studies provided rich information on the (non) existence of the RAE in women's football in specific populations and periods. However, it is still unknown if RAE has been affected by the increase in the number of women's football practitioners in the past decades²⁶ as well as the differences in the RAE between practitioners of different positions and nationalities over time.

The present study intends to investigate these gaps in the literature on age, performance, and position in women's football. Therefore, this study aimed to investigate the APP and the RAE of elite women's football players and to analyze these phenomena over time and in athletes from different nationalities and playing positions.

Methods

Three methods are usually used to identify the APP in elite sports in the scientific literature: using the age at which top athletes achieve their best performance; calculating the age of top athletes competing at events such as the Olympics and World Championship, or analyzing the age-related career performance of top athletes²⁷. This investigation is based on the age of the top athletes competing in the Summer Olympic Games from 1996 to 2016.

Data collection

Birth dates, playing positions, and nationality of all players registered in the women's football competition Olympic Games (1996 to 2016) were collected. The lower limit (1996) was defined based on the first edition of women's football at the Olympics and the upper limit (2016) represents the most recent edition at the time of this study. All data used in this study were obtained from the official website of the Federation Internationale de Football Association (www.fifa.com). The sample size of the study comprised 1,203 players.

Procedures and data analysis

Based on the birth dates, we calculated the age of the players in the different editions of the Olympic games. Descriptive statistics (mean, standard deviation, minimum, maximum) were used to summarize the collected data. The Lilliefors test was used to test data normality. The relationship between team average age and sports performance was analyzed using Spearman's correlation coefficient and the Mann-Whitney U Test (comparison between medalist and non-medalist teams). The Kruskal Wallis test was used to analyze the age of the players from different positions and seasons. Dunn's posthoc test was used when significant differences were found.

The birth month of each player was classified into four quarters. The cut-off date in FIFA championships is January 1st. The first quarter (Q1) represents January, February, and March; the second quarter (Q2) represents April, May, and June; the third quarter (Q3) represents July, August, and September; and the last quarter (Q4) represents October, November, and December. Absolute and relative frequencies were used to summarize the collected data. A Pearson's Chi-Square test and odds ratios (OR) were used to assess the differences between the observed and expected birth months’ distributions. The expected frequencies are based on the equally distributed birth rate over the year. This choice was made given the difficulty of accessing the birth statistics of each studied population¹⁶. To assess the magnitude of the effect size for the chi-square analyses, Cramer's V was used^{17, 25}. For the interpretation of the results, V between 0.06 and 0.17 was considered a small effect, from 0.18 to 0.29 was considered a medium effect, and above 0.30 was considered a large effect²⁸. A standardized residual was also calculated, as suggested by Sharpe²⁹, and interpreted as significant when exceeding z>|2.0|. To compare the average age of the players among the six seasons, the Kruskal Wallis test with Dunn's post-hoc was used. The level of significance was set at p < 0.05. All analyses were performed using MATLAB (TheMathWorks).

Result

Figure 1 shows the age distribution of all the players from 1996 to 2016. We found an average age of 25.1 ± 4.0 years old, with 16 and 41 the minimum and maximum age, respectively.

Figure 1
Age distribution of women's football players in Olympic Games from 1996 to 2016.

Figure 2 shows the average age of the players in the six seasons. We found an increase of 1.4 years in the average age from 1996 (25 ± 3.9 years old) to 2016 (26.4 ± 3.7 years old). The average age in 2016 was significantly higher than the 1996, 2000, 2004 and 2008 seasons (H(5) =32.29; p < 0.001).

Figure 2
The average age of women's football players in the Olympic Games from 1996 to 2016.

Table 1 shows the average age of the players in different tactical positions over the six seasons of the tournament. Only the forwards showed an increase in average age from 2004 and 2008 to 2016 (H(5) = 12.70; p < 0.001), while players from other positions showed no difference between the seasons.

Table 1
Age of the players in different tactical positions in the Olympic Games from 1996 to 2016.

	1996	2000	2004	2008	2012	2016	p-value
Goalkeeper	26.9 (4.4)	24.8 (4.1)	25.1 (3.8)	25.8 (4.4)	27.9 (5.4)	27.1 (4.0)	0.090
Fullbacker	25.0 (3.4)	25.0 (3.9)	25.1 (4.5)	25.2 (4.2)	25.6 (4.2)	25.6 (3.4)	0.142
Midfielder	24.6 (4.0)	24.7 (4.2)	24.1 (3.8)	24.8 (3.8)	24.9 (4.4)	26.2 (3.9)	0.066
Forward	24.6 (4.1)	24.0 (3.6)	23.5 (4.0)	23.7 (3.5)	24.7 (3.6)	25.9 (3.9)	0.026

Legend: data expressed as mean (STD).

The comparison of players’ age between the playing positions reveals that goalkeepers are older than midfielders and forwards, and fullbackers are older than forwarders (Figure 3) (H(3) = 19.76; p < 0.001).

Figure 3
Age of peak performance in women's football according to playing positions.

Table 2 shows the birth month distribution in each season. We found a small effect size and a non-significant standardized residual in all seasons indicating the absence of RAE in elite women's players at the Olympic Games.

Table 2
Distribution of the birth months of women's football players in Summer Olympic Games.

Season		Q1	Q2	Q3	Q4	Chi-Square	p-value	OR Q1/Q4	V	Effect
1996	f (%)	41 (27%)	49 (33%)	28 (19%)	32 (21%)	7.066	0.066	1.28	0.125	Small
	Std. Res	0.4	1.6	−1.2	−0.8
2000	f (%)	45 (26%)	58 (34%)	31 (18%)	39 (23%)	9.047	0.029	1.15	0.131	Small
	Std. Res	0.2	1.8	−1.4	0.4
2004	f (%)	53 (25%)	58 (27%)	50 (23%)	54 (25%)	0.660	0.882	0.98	0.030	Small
	Std. Res	0.0	0.4	−0.4	0.0
2008	f (%)	49 (23%)	61 (28%)	60 (28%)	47 (22%)	2.944	0.400	1.04	0.067	Small
	Std. Res	−0.4	0.6	0.6	−0.6
2012	f (%)	62 (28%)	52 (24%)	65 (30%)	41 (19%)	6.436	0.096	1.51	0.098	Small
	Std. Res	0.6	−0.2	1.0	−1.2
2016	f (%)	58 (26%)	58 (26%)	62 (28%)	41 (19%)	4.907	0.178	1.41	0.085	Small
	Std. Res	0.2	0.2	0.6	−1.2

Table 3 shows the distribution of the birth months by playing position. No RAE was found in goalkeepers, fullbacks, and midfielders. Although a significant RAE was found in forwards, the magnitude of effect reveals a small effect size and a non-significant standardized residual.

Table 3
Distribution of the birth months by playing position in all Olympic Games (1996-2016).

Season		Q1	Q2	Q3	Q4	Chi-Square	p-value	OR Q1/Q4	V	Effect
Goalkeeper	f (%)	53 (27%)	53 (27%)	53 (27%)	34 (18%)	5.611	0.130	1.55	0.098	Small
	Std. Res	0.4	0.4	0.4	−1.4
Fullback	f (%)	123 (25%)	143 (29%)	102 (21%)	120 (25%)	6.934	0.074	1.02	0.068	Small
	Std. Res	0.0	0.8	−0.8	0.0
Midfilder	f (%)	139 (27%)	136 (27%)	106 (21%)	126 (25%)	5.260	0.150	1.10	0.058	Small
	Std. Res	0.4	0.4	−0.8	0.0
Forward	f (%)	96 (27%)	105 (30%)	72 (21%)	78 (22%)	8.172	0.042	1.23	0.087	Small
	Std. Res	0.0	1.0	−0.8	−0.6

Discussion

This study aimed to investigate the relative age effect and the age of peak performance of women's football players who participated in the Olympic Games from 1996 to 2016. We found the current average age of 26 years old (SD = 4.0) with an aging trend over the years. The goalkeepers showed the highest average age (26.2 ± 4.4 years), while the forwards are the youngest players (24.4 ± 3.8 years). The analysis of the birth months showed neither RAE in women's football players over the years nor in different playing positions. Such information is useful in the decisions of athlete selection for major competition and in allocating funding and resources based on an athlete's chances of success^{30, 31}.

The analysis of the average age and the standard deviations of women's football players showed that most of the athletes’ age is between 21 and 29 years old. Although we found an increase in the average age in the last edition (2016), athletes remain below 30 years old. It is known that the game consists of stimuli of high-intensity aerobic and speed endurance fitness^{32, 33}, requiring a high fitness of the resistance strength, agility, and speed capacities of the athletes^{34, 35}. The intermittent feature of the sport, coupled with high physical demand, limits the age of peak performance. The results of this study corroborate that sports that require a high fitness of strength and power capacities limit the APP until the 30 years old³⁶.

The average age of women's football players showed an increase of 1.4 years in the last two decades. The same pattern of increasing average age over the years was recently found in men's football⁶. According to the authors⁶, the development of science, multidisciplinary work, and greater support for the athletes, made possible their greater permanence in the sport. Although women receive less investment than men, the increased support received over time may have contributed to extending their careers. It is possible that, even with the social barriers that still exist for the participation of women in sport, the sports development system is providing better opportunities and support for the players allowing them to extend their careers.

The sample analyzed in this study also contributes to explaining the increase in average age. International championships, such as the Olympic Games, are characterized by full stadiums with a high demand for sports performance. Athletes’ performance might be negatively affected by the stressful environment if they are not familiarized with it³⁷. Therefore, being older and having previous experiences in the competition are important for the development of coping strategies and effectiveness³⁸. Furthermore, lower rates of player turnover may be beneficial for team performance in women's football championship at elite level³⁷. Maintaining teammates together for a longer period might improve human and social capital³⁷. Consequently, increasing the team's average age might be beneficial for performance. These results reinforce the need to prolong women's football players’ careers, thought greater support for the athletes, allowing their physical, technical, and tactical development throughout a long-term training program.

The analysis by playing position in women's football revealed that goalkeepers and defenders are older than forwarders corroborating previous findings in men's football⁶. The lower physical demand for goalkeepers and defenders is possible one of the reasons they tend to peak at a later age and maintain a high performance higher up in age⁶. For instance, it is known that defenders perform less high-intensity running during a game than midfielders and attackers³⁹. On the contrary, the higher amount of high-intensity activity performed by forwarders^{32, 33} is probably one of the causes of the earlier APP.

The results of this study corroborate previous findings of no existence of RAEs in women's football national teams^{17, 22, 23, 25, 40}. As a possible and optimistic explanation, women's football has been recently practiced in high performance (e.g. the first FIFA Women's World Cup was established in 1991) and, possibly, it is being structured in order to avoid the RAE phenomenon. The sports development system provides the players a fair structure for long-term development without favoring those born at the beginning of the year and who have psychophysiological advantages. We suggest that these hypotheses should be investigated by future studies. But, the lack of RAE might also indicate that, although female football players have increased 38% since 2000²⁶, a greater number of athletes does not seem enough to increase the competition in selection and, consequently, the occurrence of RAE. Women still face disadvantages accessing and developing in sports and, consequently, there is less competition and less selection for the entrance and development in the sport compared to men²².

Lastly, to compare the observed and expected frequency of birth we assumed a uniform distribution over the months. It should be recognized that the assumption of uniform wider populations for all gender, region, and age subgroups is a limitation of our study⁴¹.

Conclusion

In this study, we investigated the age and birth date of players in one of the main events in elite women's football, the Summer Olympic Games. We found the current average age of 26.4 years old in elite football players and an aging trend in the past two decades. Coaches should consider the differences between players from different playing positions to program long-term training. We found the highest average age in goalkeepers (26 years old) and the youngest players as the forwards (24.4 years old). This knowledge provides valuable information to coaches and professionals involved in training to program, plan and promote athlete's progression towards their performance targets. The analysis of the birth months showed neither RAE in women's football players over the years nor in different playing positions. There is the need for future studies that assess whether the absence of RAE remains as the recruiting bias does not benefit player development or on-field success.

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Associate Editor: Dustin Jay Oranchuk, Auckland University of Technology, Sports Performance Research Institute New Zealand, Sprinz, New Zealand.

Publication Dates

• Publication in this collection
  01 Sept 2021
• Date of issue
  2021

History

• Received
  07 Apr 2021
• Accepted
  01 Aug 2021