Training & Testing
Effect of Birth Month on Physical Fitness of Soccer Players (Under-15) According to Biological Maturity
A uthors
I. Fragoso', L. M. Massuca2, J. Ferreira1
A ffiliations
1 Faculty o f Human Kinetics, Technical University o f Lisbon, Cruz-Quebrada, Portugal 2 Faculty o f Physical Education and Sport, Lusofona University, Lisbon, Portugal
Key w o rd s
Abstract
O anthropom etry
▼
O fitness
This study aims to clarify the relationship between the birth quarters, biological maturity and physical fitness (PF) in Under-15 youth soc cer players. Each participant (n=133) was an Under-15 player from a top-elite soccer acad emy. The data collection period lasted 8 years (from Under-15 2002/2003 to 2009/2010 sea son). The athletes’ birth dates were recorded and organized by birth quarters (Ql, first; Q2, sec ond; Q3, third; Q4, fourth) and by semesters (SI, first; S2, second). Additionally recorded were each athlete’s biological maturity (skeletal age, SA), anthropometric profile (stature; body mass;
O relative age effect O skeletal age O talent identification
Introduction ▼
accepted a fte r revision May 30, 2014
Bibliography DOI http://dx.doi.org/
10.1055/S-0034-1384548 Published online: A u g u s t2 1 ,2014 IntJ Sports Med 2015; 36: 16-21 © Georg Thieme Verlag KG S tuttgart • New York ISSN 0172-4622
Correspondence Prof. Luis Miguel Massuca Faculty of Physical Education and Sport Lusofona University Campo Grande 376 1749-024 Lisbon Portugal Tel.: +351/967/033 079 [email protected]
Sports agents nowadays increasingly think about concepts such as talent prediction (for a specific sport) and future ability prediction (of youth ath letes). To satisfy sports agents’ curiosity, it is becoming an absolute necessity to identify the predictive indicators of a young athlete's future success. Soccer scouts and specially coaches search incessantly for the “solution", factors that enable them to understand the possible develop ment and future ability of each young athlete. Because the ideal age for identifying talented individuals is specific for each particular sport, it is not easy to generalize critical or sensitive peri ods for identifying and selecting gifted players [22,42 ]. In sports requiring high levels of physical fitness [7,8], early recruitment based on condi tional abilities may result in misjudgements, as some of those abilities will not be developed until late puberty [22,27,28,38,42]. Puberty begins with gonadarche, which is achieved when the pulsatile secretion of GnRH reaches the nec essary frequency and amplitude. One of the most evident changes is the sudden increase in pubic
Fragoso I et al. Effect of Birth Month... IntJ Sports Med 2015; 36:16-21
thigh, calf and upper arm girths), and fitness pro file (10-m and 30-m sprint times; SJ; CMJ; shut tles in YYiR Test). Significant differences were found for (1) decimal age and SA by quarters (Q4-Q1, Q2) and semesters; and (2) stature (Q3Ql, Q2, Q4; S1-S2), body mass (Q1-Q3; S1-S2), thigh girth (S1-S2), SJ (Q1-Q2) and sprint time (Q4-Q1, Q2; S1-S2). When maturity was consid ered as covariate all PF variables, with exception of SJ (Q1-Q2) and 10-m sprint time (S1-S2), were very similar among the studied groups. These findings suggest that (1) seasonal birth effect may result from the observed biological matura tion differences, and (2) athletes may have been chosen due to their PF attributes.
hair density and the beginning of the develop ment of breasts. However, puberty is extended during the whole period of the secondary sex characteristics maturation. It is well documented that playing soccer demands great aerobic and anaerobic capacity, as well as great muscular strength in terms of speed [7,8], which are characteristics that, from a physical fitness point of view, should be considered only after the onset of puberty and never before [28,38]. According to literature [34], the repeatedsprint ability performance among highly trained youth soccer players improved during growth at adolescence, while improvements were nearly imperceptive after the age of 15. The identification of some key morphological and fitness attributes may lead to a better under standing of athletic success. The most addressed factors in sports talent-related literature are morphological [5,11,17,25,30,33] and fitness [9, 20,26] characteristics and profiles. However, this information can be accurate only if we take into account the athlete's biological age or biological maturity. The term maturity is understood as a state following a long process of maturation that
Training & Testing
only ends when reaching adulthood in all tissues, organs and systems or the limit of any functional ability. However, we believe that this functionality measure (state) can be deter mined for all ages as long as standardized references can be obtained for the variables and ages in the study. Therefore, we can consider the distance between the 2 extremes of this proc ess as an important indicator through which it is possible to: collect information regarding the “journey” made by each indi vidual towards a final stage; compare the state of the subject’s functional abilities against benchmarks; and obtain standard values of growth and development in children and adolescents [17,25,29], To better understand this problematic, sports scientists have studied: (1) the impact of biological maturity on anthropomet ric and functional characteristics of youth soccer players [17,28]; (2) the impact of birth age effect, which is defined as the differ ences in age between children born in the same competition year, on anthropometric profile when considering athlete bio logical maturity [25]; and (3) the relationship between maturity, anthropometric characteristics, fitness attributes and birthdate in under-15 (U15) elite youth academy soccer players [26]. 3 explanations have been offered to illustrate the importance of maturity and birth age effect to the identification of sports tal ent [24]. Firstly, the procedures used in the identification and discovery of talents are strongly biased towards the physical characteristics of the child, instead of emphasizing the evolution of learning and technical abilities. Secondly, the competitive organization complies with 24-month periods, making the play ers’ physical characteristics an important choice factor. Finally, this circumstance is particularly true for sports that have demanding competitive calendars starting at early ages. The association between morphology, levels of maturity and performance has been frequently considered in a youth sports context. Boys who are early mature are generally more prone to success in most types of exercise, particularly in those that involve strength, velocity and power [32], In addition, many studies point to a higher frequency of athletes born during the first months of the year in sports like ice-hockey, cricket, base ball and tennis [1,4,10], This effect is even more noticeable in young elite teams [3], Concerning football, the birth age effect is a reality observed in very different countries, such as Japan, Brazil, Australia, Germany or Portugal [18,35,36]. However, very few studies to date have considered, the relationship between maturity, birth date and physical fitness attributes in young soccer players, the results being contradictory and therefore unsustainable. Thus, the aim of this study was to clarify the relationship between birth distri bution and a precise measure of biological maturity and, armed with this knowledge, to better understand the relationship between these biological conditions and the physical fitness attributes in U15 elite youth soccer players.
Material & Methods ▼
The protocol implemented was designed according to the Hel sinki Declaration and approved by local science and ethics com mittees, and met the ethical standards of the IJSM [21 ]. Prior to inclusion in this study, all subjects and guardians were informed of the goals and procedures of the study, and guardians gave a written consent.
Participants
A total of 133 Portuguese U15 elite soccer players (from a Portu guese top elite soccer academy) were studied (decimal age, 14.3+0.6 years; stature, 167.8 +7.8cm; body mass, 57.5±8.5kg; skeletal age, 14.8 ±1.2 years). The data collection period lasted 8 years (from the 2002/2003 to 2009/2010 season). All subjects (including some of the actual best players in Europe; e.g., soccer players from actual top elite senior teams in Premier League, BBVALeague and French Football League) were tested once (only U15s). Based on their respective birthdates, the participants were grouped: (1) by birth quarters (first quarter or Q1 - from January to March, n =60; 45.1%; second quarter or Q2 - from April to June, n=43, 32.3%; third quarter or Q3 - from July to September, n=22,16.6%; fourth quarter or Q4 - from October to December, n =8, 6.0%); and (2) by semesters (first half - from January to June, n =103, 77.4%; second half - from July to December, n =30,22.6%). Biological maturity
The maturational evaluation consisted of calculating the skeletal age (SA) using the Tanner-Whitehouse III Method (i.e., TW3) [41]. In this process, skeletal age was evaluated by a highly skilled technician who had read more than 2 000 X-rays. Every 6 months this technician compared his readings with the readings of an expert (one of the authors of the TW III Method), and an inter-examiner reliability (intraclass correlation coefficient [ICC]) was calculated (ICC range: 0.86-0.98). Anthropometric profiling
5 anthropometric variables were determined. We obtained 2 basic measures and 3 girths. The 2 basic measures were stature (cm) and body mass (kg). The 3 girths were thigh girth, calf girth and upper arm girth (all in cm). All such measurements were obtained using portable measurement devices, i.e.: (1) Stature was measured using a portable anthropometer (GPM, SiberHegner, Switzerland); (2) body mass was measured, to the near est 0.5 kg, using a scale (Secca model 761 7019009, Vogel & Halke, Germany); and (3) girths were measured using a flexible, non-stretching steel tape (W606PM, Lufkin, USA). All measure ments were taken by 4 technicians accredited by International Society for the Advancement of Kinanthropometry (ISAK), and according to the ISAK procedures [31] (intra-observer technical error of measurements: stature, R>0.98; girths, R= [0.92-00.98]). Fitness profiling
Before the fitness tests, all participants performed a 20-min warm-up (involving a slow jog followed by static and dynamic stretching). They were also allowed a 10-min passive rest between tests. Water breaks and extra rest time were also allowed. Each player was both instructed and verbally encour aged to give his maximal effort. Participants performed 4 tests (according to the order described), and 5 variables were recorded for analysis. The tests included a 30-m speed test. The best score (time in seconds) of the 3 trials, at 10-m and 30-m, was recorded for analysis [15]. All sprint times were recorded using electronic timing lights (wireless sprint system, Brower Timing Systems, Salt Lake City, Utah, USA). The players performed 2 vertical jump tests on an Ergojump (Bosco System, Globus, Italy) using the Bosco protocol [6] to determine lower body explosive strength. 3 trials of each test (squat jump, SJ; countermovement jump, CMJ)
Fragoso I et al. Effect of Birth Month... IntJ Sports Med 2015; 36; 16-21
17
Training & Testing
were performed and, the best trial result of each was recorded (height; in cm). Finally, to study intermittent endurance capac ity, the Yo-Yo intermittent recovery test (YYIRT) was used [2], and the number of the last shuttle run was recorded (#). Statistical analysis
The descriptive and comparative summary data are presented, and group data are expressed as mean (M) and standard devia tion (SD) for dependent variables, i.e., M±SD. The significant dif ferences among the average maturity, anthropometric and fitness variables of athletes born in the 4 birth quarters of the year were evaluated using one-way ANOVA followed by a multi ple comparisons test (LSD). The significant differences between the average maturity, anthropometric and fitness variables of athletes born in the first semester and in the second semester were evaluated with the T-Student test for independent sam ples. The effect of the birth “quarters” and “semester” on anthro pometric and fitness variables were evaluated separately with an ANCOVA (using the skeletal age as covariant) after the vari ance-covariance homogeneity assumptions were validated with the M Box test. All statistical analyses were conducted with sig nificance set at 5% using the Statistical Package for the Social Sciences (SPSS Inc, version 17.0, Chicago, Illinois).
Results ▼
Significant differences were observed between skeletal and dec imal age, both when compared by birth quarters (decimal age, F(3,129) =6.147, p
Effect of Birth Month on Physical Fitness of Soccer Players (Under-15) According to Biological Maturity
A uthors
I. Fragoso', L. M. Massuca2, J. Ferreira1
A ffiliations
1 Faculty o f Human Kinetics, Technical University o f Lisbon, Cruz-Quebrada, Portugal 2 Faculty o f Physical Education and Sport, Lusofona University, Lisbon, Portugal
Key w o rd s
Abstract
O anthropom etry
▼
O fitness
This study aims to clarify the relationship between the birth quarters, biological maturity and physical fitness (PF) in Under-15 youth soc cer players. Each participant (n=133) was an Under-15 player from a top-elite soccer acad emy. The data collection period lasted 8 years (from Under-15 2002/2003 to 2009/2010 sea son). The athletes’ birth dates were recorded and organized by birth quarters (Ql, first; Q2, sec ond; Q3, third; Q4, fourth) and by semesters (SI, first; S2, second). Additionally recorded were each athlete’s biological maturity (skeletal age, SA), anthropometric profile (stature; body mass;
O relative age effect O skeletal age O talent identification
Introduction ▼
accepted a fte r revision May 30, 2014
Bibliography DOI http://dx.doi.org/
10.1055/S-0034-1384548 Published online: A u g u s t2 1 ,2014 IntJ Sports Med 2015; 36: 16-21 © Georg Thieme Verlag KG S tuttgart • New York ISSN 0172-4622
Correspondence Prof. Luis Miguel Massuca Faculty of Physical Education and Sport Lusofona University Campo Grande 376 1749-024 Lisbon Portugal Tel.: +351/967/033 079 [email protected]
Sports agents nowadays increasingly think about concepts such as talent prediction (for a specific sport) and future ability prediction (of youth ath letes). To satisfy sports agents’ curiosity, it is becoming an absolute necessity to identify the predictive indicators of a young athlete's future success. Soccer scouts and specially coaches search incessantly for the “solution", factors that enable them to understand the possible develop ment and future ability of each young athlete. Because the ideal age for identifying talented individuals is specific for each particular sport, it is not easy to generalize critical or sensitive peri ods for identifying and selecting gifted players [22,42 ]. In sports requiring high levels of physical fitness [7,8], early recruitment based on condi tional abilities may result in misjudgements, as some of those abilities will not be developed until late puberty [22,27,28,38,42]. Puberty begins with gonadarche, which is achieved when the pulsatile secretion of GnRH reaches the nec essary frequency and amplitude. One of the most evident changes is the sudden increase in pubic
Fragoso I et al. Effect of Birth Month... IntJ Sports Med 2015; 36:16-21
thigh, calf and upper arm girths), and fitness pro file (10-m and 30-m sprint times; SJ; CMJ; shut tles in YYiR Test). Significant differences were found for (1) decimal age and SA by quarters (Q4-Q1, Q2) and semesters; and (2) stature (Q3Ql, Q2, Q4; S1-S2), body mass (Q1-Q3; S1-S2), thigh girth (S1-S2), SJ (Q1-Q2) and sprint time (Q4-Q1, Q2; S1-S2). When maturity was consid ered as covariate all PF variables, with exception of SJ (Q1-Q2) and 10-m sprint time (S1-S2), were very similar among the studied groups. These findings suggest that (1) seasonal birth effect may result from the observed biological matura tion differences, and (2) athletes may have been chosen due to their PF attributes.
hair density and the beginning of the develop ment of breasts. However, puberty is extended during the whole period of the secondary sex characteristics maturation. It is well documented that playing soccer demands great aerobic and anaerobic capacity, as well as great muscular strength in terms of speed [7,8], which are characteristics that, from a physical fitness point of view, should be considered only after the onset of puberty and never before [28,38]. According to literature [34], the repeatedsprint ability performance among highly trained youth soccer players improved during growth at adolescence, while improvements were nearly imperceptive after the age of 15. The identification of some key morphological and fitness attributes may lead to a better under standing of athletic success. The most addressed factors in sports talent-related literature are morphological [5,11,17,25,30,33] and fitness [9, 20,26] characteristics and profiles. However, this information can be accurate only if we take into account the athlete's biological age or biological maturity. The term maturity is understood as a state following a long process of maturation that
Training & Testing
only ends when reaching adulthood in all tissues, organs and systems or the limit of any functional ability. However, we believe that this functionality measure (state) can be deter mined for all ages as long as standardized references can be obtained for the variables and ages in the study. Therefore, we can consider the distance between the 2 extremes of this proc ess as an important indicator through which it is possible to: collect information regarding the “journey” made by each indi vidual towards a final stage; compare the state of the subject’s functional abilities against benchmarks; and obtain standard values of growth and development in children and adolescents [17,25,29], To better understand this problematic, sports scientists have studied: (1) the impact of biological maturity on anthropomet ric and functional characteristics of youth soccer players [17,28]; (2) the impact of birth age effect, which is defined as the differ ences in age between children born in the same competition year, on anthropometric profile when considering athlete bio logical maturity [25]; and (3) the relationship between maturity, anthropometric characteristics, fitness attributes and birthdate in under-15 (U15) elite youth academy soccer players [26]. 3 explanations have been offered to illustrate the importance of maturity and birth age effect to the identification of sports tal ent [24]. Firstly, the procedures used in the identification and discovery of talents are strongly biased towards the physical characteristics of the child, instead of emphasizing the evolution of learning and technical abilities. Secondly, the competitive organization complies with 24-month periods, making the play ers’ physical characteristics an important choice factor. Finally, this circumstance is particularly true for sports that have demanding competitive calendars starting at early ages. The association between morphology, levels of maturity and performance has been frequently considered in a youth sports context. Boys who are early mature are generally more prone to success in most types of exercise, particularly in those that involve strength, velocity and power [32], In addition, many studies point to a higher frequency of athletes born during the first months of the year in sports like ice-hockey, cricket, base ball and tennis [1,4,10], This effect is even more noticeable in young elite teams [3], Concerning football, the birth age effect is a reality observed in very different countries, such as Japan, Brazil, Australia, Germany or Portugal [18,35,36]. However, very few studies to date have considered, the relationship between maturity, birth date and physical fitness attributes in young soccer players, the results being contradictory and therefore unsustainable. Thus, the aim of this study was to clarify the relationship between birth distri bution and a precise measure of biological maturity and, armed with this knowledge, to better understand the relationship between these biological conditions and the physical fitness attributes in U15 elite youth soccer players.
Material & Methods ▼
The protocol implemented was designed according to the Hel sinki Declaration and approved by local science and ethics com mittees, and met the ethical standards of the IJSM [21 ]. Prior to inclusion in this study, all subjects and guardians were informed of the goals and procedures of the study, and guardians gave a written consent.
Participants
A total of 133 Portuguese U15 elite soccer players (from a Portu guese top elite soccer academy) were studied (decimal age, 14.3+0.6 years; stature, 167.8 +7.8cm; body mass, 57.5±8.5kg; skeletal age, 14.8 ±1.2 years). The data collection period lasted 8 years (from the 2002/2003 to 2009/2010 season). All subjects (including some of the actual best players in Europe; e.g., soccer players from actual top elite senior teams in Premier League, BBVALeague and French Football League) were tested once (only U15s). Based on their respective birthdates, the participants were grouped: (1) by birth quarters (first quarter or Q1 - from January to March, n =60; 45.1%; second quarter or Q2 - from April to June, n=43, 32.3%; third quarter or Q3 - from July to September, n=22,16.6%; fourth quarter or Q4 - from October to December, n =8, 6.0%); and (2) by semesters (first half - from January to June, n =103, 77.4%; second half - from July to December, n =30,22.6%). Biological maturity
The maturational evaluation consisted of calculating the skeletal age (SA) using the Tanner-Whitehouse III Method (i.e., TW3) [41]. In this process, skeletal age was evaluated by a highly skilled technician who had read more than 2 000 X-rays. Every 6 months this technician compared his readings with the readings of an expert (one of the authors of the TW III Method), and an inter-examiner reliability (intraclass correlation coefficient [ICC]) was calculated (ICC range: 0.86-0.98). Anthropometric profiling
5 anthropometric variables were determined. We obtained 2 basic measures and 3 girths. The 2 basic measures were stature (cm) and body mass (kg). The 3 girths were thigh girth, calf girth and upper arm girth (all in cm). All such measurements were obtained using portable measurement devices, i.e.: (1) Stature was measured using a portable anthropometer (GPM, SiberHegner, Switzerland); (2) body mass was measured, to the near est 0.5 kg, using a scale (Secca model 761 7019009, Vogel & Halke, Germany); and (3) girths were measured using a flexible, non-stretching steel tape (W606PM, Lufkin, USA). All measure ments were taken by 4 technicians accredited by International Society for the Advancement of Kinanthropometry (ISAK), and according to the ISAK procedures [31] (intra-observer technical error of measurements: stature, R>0.98; girths, R= [0.92-00.98]). Fitness profiling
Before the fitness tests, all participants performed a 20-min warm-up (involving a slow jog followed by static and dynamic stretching). They were also allowed a 10-min passive rest between tests. Water breaks and extra rest time were also allowed. Each player was both instructed and verbally encour aged to give his maximal effort. Participants performed 4 tests (according to the order described), and 5 variables were recorded for analysis. The tests included a 30-m speed test. The best score (time in seconds) of the 3 trials, at 10-m and 30-m, was recorded for analysis [15]. All sprint times were recorded using electronic timing lights (wireless sprint system, Brower Timing Systems, Salt Lake City, Utah, USA). The players performed 2 vertical jump tests on an Ergojump (Bosco System, Globus, Italy) using the Bosco protocol [6] to determine lower body explosive strength. 3 trials of each test (squat jump, SJ; countermovement jump, CMJ)
Fragoso I et al. Effect of Birth Month... IntJ Sports Med 2015; 36; 16-21
17
Training & Testing
were performed and, the best trial result of each was recorded (height; in cm). Finally, to study intermittent endurance capac ity, the Yo-Yo intermittent recovery test (YYIRT) was used [2], and the number of the last shuttle run was recorded (#). Statistical analysis
The descriptive and comparative summary data are presented, and group data are expressed as mean (M) and standard devia tion (SD) for dependent variables, i.e., M±SD. The significant dif ferences among the average maturity, anthropometric and fitness variables of athletes born in the 4 birth quarters of the year were evaluated using one-way ANOVA followed by a multi ple comparisons test (LSD). The significant differences between the average maturity, anthropometric and fitness variables of athletes born in the first semester and in the second semester were evaluated with the T-Student test for independent sam ples. The effect of the birth “quarters” and “semester” on anthro pometric and fitness variables were evaluated separately with an ANCOVA (using the skeletal age as covariant) after the vari ance-covariance homogeneity assumptions were validated with the M Box test. All statistical analyses were conducted with sig nificance set at 5% using the Statistical Package for the Social Sciences (SPSS Inc, version 17.0, Chicago, Illinois).
Results ▼
Significant differences were observed between skeletal and dec imal age, both when compared by birth quarters (decimal age, F(3,129) =6.147, p
