RELATIVE AGE EFFECT AND SELECTION OF YOUNG BASKETBALL PLAYERS

Purpose of the present study was to examine whether infl uence of relative age effect (RAE) exists or not in the selected 13 year old basketball players. Subjects were 20 basketball players (HT=177.35cm±6.73, BW=61.42kg±8.98, average age 13 years and 7 months ±.28, average experience in basketball training 4 years and 6 months ±1.15). Sample was divided in two groups: 11 players born in fi rst half of the year and 9 players born in the second half of the year. One-way ANOVA was used in order to analyze the differences between the two groups of players in set of anthropometric variables (body height, arm span, standing reach height, body weight and percentage of body fat), motor variables (velocity of neuromuscular reaction time, vertical jump, 5 meters sprint, 10 meters sprint, 20 meters sprint, T-test, Zig-zag test, ball throw from sitting position, Sit-ups for 30 seconds and standing forward bend) and one functional variable (20-M shuttle run test). Subjects do not differ in applied set of parameters, except in on variable (sit-ups for 30 seconds, p=.040). It was concluded that RAE does not exist in this sample of examinees.


INTRODUCTION
Puberty is the period of growth where human's body size rapidly develops.During the fi rst and second year of puberty, annual growth is 8-12 cm (Marković, & Bradić, 2009).This period is called adolescent growth spurt.The beginning of the adolescent growth spurt and year of the most significant annual growth are indicators of child maturity.Children who enter puberty earlier than average age are called accelerants.On the other side, there are children who enter puberty later than average age.This is particularly important information because accelerants, at that moment have signifi cantly betterdeveloped motor and functional abilities than their peers hence have potential advantage in selection process.In that way, that children sometimes can be privileged in basketball, compare to children who mature lately.Although these advantages disappear with maturation to adulthood, it can result in a loss of certain number of talented basketball players.
In last thirty odd years, children begin with basketball earlier than their fathers and mothers did.The same situation goes for many other modern era athletes -Wayne Gretzky, one of the best hockey players of all time, fi rst time used skates aged three (Morrison, 2011).Early introduction to basketball training creates conditions of early adoption of basketball skills such are shooting, passing, ball control, movement without ball etc.However, early introduc-tion to basketball training makes children born within fi rst six months of calendar year privileged (Addona, & Yates, 2010)!Following two examples support that notion.Example 1: there is a running competition in sport school of fi ve years old boys.One was born in January, and other one in December of the same year.Five years old boy born in January is almost 20% older than boy born in December.Older boy was a little bit faster.Does this mean that he will be always faster than his peer?Example 2: In "basketball shool", eight and nine year old boys train together.
In play one on one, boy born in January dominates his 23 months younger opponent.Does this mean that currently better player will be better for 10 or 15 years, when they will become "real" basketball players?Some coaches (not just basketball ones) will give advantage in selection to currently better players, ignoring just described phenomenon.The phenomenon that we talk about is called the Relative age effect (RAE).RAE was discovered when Barnsley, Thompson and Bamsley (1985) were analysing data from Canadian-American professional hockey league (NHL) -season 1982/1983.During that season, almost double numbers of players were born within fi rst quarter of the year (32% from January to March), than in last quarter (16.2% from October to december).RAE was more drastic in younger hockey leagues in Canada, where ratio of players who were born in the fi rst quarter was three times greater than in the last quarter of the year.There are numerous evidences of the existence of RAE phenomenon (Malina, Bouchard, & Bar-Or, 2004).In an extensive study, Torres-Unda et al., (2013) analysed Relative age effect.They studied association of anthropometric and physiological characteristics with maturity of young basketball players (aged 13 and 14) and their basketball successfulness.Anthropometric parameters were: length measures, body mass and skinfolds.Stamina, 20m dash, jump and dribbling speed tests were utilized to assess physiological parameters.Analysis of the anthropometric characteristics showed that better basketball players were taller, heavier and more muscular.Physiological tests confi rmed higher quality of better basketball players in jumping, stamina, agility (especially with the ball) and speed tests.These skills correlated with average points scored in the competitive season.Most of the selected (better) basketball players were born in the fi rst half of the year.It means that coaches mainly chose more mature players.Findings of study conducted by Delorm, Chalabaev and Raspaud (2011) confi rmed that RAE should be taken into account when considering children who leave basketball and who were born in the second half of the year.Addona and Yates (2010) claim that globally nothing is done to prevent RAE.Meanwhile, experienced basketball coaches for years are warning younger colleagues to avoid the trap of promoting biologically older children.This was subject of debates in many seminars.Coaches mutually exchange experiences and it could be said that signifi cant attention is given to RAE as a potential threat.Many coaches know the proverb: "If you want good basketball player, look for tall parents, ex players if possible".If a child is the tallest player in a selection, it is unlikely that coach will ignore that, even if he was born in the second half of the year.Certainly, there are coaches who will, for selfi sh interest and short-term success (champions of the state in the youngest category for example), push children who are physically dominant at that moment.
Purpose of this study was to examine whether infl uence of the effect of relative age (ERA) exists or not in the selected 13 year old basketball players.Considering earlier studies on RAE, it could be presumed that older group of basketball players will achieve better results in all tested variables.Obtained results helped coaches to get to know about ERA issue and in very convincing and exact way to prove thesis that in selection process of young basketball players, those who are "late" in biological maturation should not be rejected.

METHOD Subjects
Subjects were 20 basketball players born in the same year (average age 13 years and 7 months ±.28, average experience in basketball training 4 years and 6 months ±1.15).All subjects are members of two best teams in "pioneer" category (Basketball club "Šampion-Alfom" and Basketball club tor tests and test of aerobic endurance were fi nished.Statistical computations were done by statistical software SPSS 11 (SPSS Inc., Chicago, IL, USA).Kolmogorov-Smirnov test was utilized to confi rm normal distribution.Descriptive statistics were done after that.At the end, One-way ANOVA was used in order to establish the differences between the groups.

RESULTS
Kolmogorov-Smirnov (K-S) test confi rmed that all variables had normal distribution.In Table 1, there are presented means, standard deviation and established signifi cant difference between the groups.
Based on mean values (Mean) it is noticeable that older group of basketball players (group 1) made better results in most of measured and tested variables (Table 1).Group 2 had better results in tests for assessment of the velocity of neuromuscular reaction time and 5 meters sprint.They had lower percentage of body fat, as well.Analysis of variance showed that there are no statistically signifi cant differences between basketball players born in the fi rst half of the year and basketball players born in the second half of the year in all variables, except sit-ups for 30 seconds (p<.05).
For comparison reasons, interesting are mean values of 13-year-old boys from six European countries ("Physical development and physical abilities of primary school children", 2009).These are presented in table 2, and it is clear that children from Serbia are taller and heavier than children from other fi ve European countries, but their abdominal repetitive strength is among poorer results.On the other hand, basketball players who participated in the present study are taller, heavier and have better repetitive strength of abdominal muscles than their European peers from six countries.It was expected, considering that tested subjects are actively engaged in basketball.
"Basket 2000") in region ("Areal basketball board Banjaluka") with population of 500.000inhabitants.Coaches of these two teams suggested their 10 best players each.Last year and a half they train one hour four times a week on average.Apart from training sessions, they play around twenty games in season.Eleven boys were born in the fi rst half of the year (group 1), and nine boys were born in the second half of the year (group 2).Boys gave their consent for measuring and testing procedures.

Variables
From anthropometric domain, 5 measures were taken: body height, arm span, standing reach height, body weight and percentage of body fat.Motor abilities were tested by: velocity of neuromuscular reaction time, vertical jump, 5 meters sprint, 10 meters sprint, 20 meters sprint, T-test, Zig-zag test, ball throw from sitting position, Sit-ups for 30 seconds and standing forward bend.Stamina was assessed by 20-M shuttle run test.Relative oxygen consumption was calculated by indirect method.
All measurements and tests were recommended by Reiman and Manske (2009), and body height was measured by body height measuring apparatus (SECA 210), arm span and standing reach height (centimetre tape on wall), body weight and percentage of body fat (TANITA BC 418A), velocity of neuromuscular reaction time, vertical jump, 5 meters sprint, 10 meters sprint, 20 meters sprint, T-test, Zigzag test (Physical Ability Test PAT 02, Uno Lux), ball throw from sitting position (centimetre tape), Sit-ups for 30 seconds (electronic stopwatch) and standing forward bend (Swedish bench with attached ruler).

Procedure
Measurements and testing were performed during two mornings.First day subjects had body height, arm span, standing reach height, body weight and percentage of body fat measured and one-half of motor tests.On the second day, the rest of the mo-

DISCUSSION
Present study examined whether infl uence of relative age effect (RAE) exists or not in the selected 13 year old basketball players.Results indicate that there are no statistically signifi cant differences between basketball players born in the fi rst half of the year and basketball players born in the second half of the year in most of variables (exception is variable Sit-ups for 30 sec.; p<.05).Therefore, it could be stated that there is no infl uence of RAE on basketball players' selection from the present study.It might be that similar quality of players from these two teams (best in region) was signifi cant advantage compare to other teams.It is known fact that important role in modern basketball means every position in team should be covered with quality players.It is a wish of every basketball coach to have 3 to 4 good players for each position.
Statisticians are mostly dealing with the phenomenon of RAE.From large databases, they check distribution of players' birthdays and relate that with their successfulness -engagement in a league of certain quality.In Côté, Macdonald, Baker and Abernethy (2006), Delorme and Raspaud (2009) studies signifi cant infl uence of RAE on NBA basketball players selection and professional French players could not be found.In season 2012/2013 of basketball Euroleague (http://www.euroleague.net/competition/players),existence of RAE is evident: analysis of players shorter than 200 cm, it could be said that more players were born in the fi rst half of the year -113, than in the second half of the year -69.As for players taller than 200 cm, the difference is smaller: 94 players were born in the fi rst half of the year, and 79 in the second half of the year.Hence, RAE is more frequent in shorter players.To the authors' knowledge, articles studying connections between athletes' physical qualities and RAE are very rare.Considering subjects' body height, results of this study are not consistent to those of Delorm and Raspaud (2009).In their study, on the population of young French players, pubertal boys born in the fi rst half of the year are signifi cantly taller than their peers born 79 in the second half of the year.Body height is the most important factor of selection in this age (Karalejić, & Jakovljević, 2001).It seems that children coaches from our study are better informed about RAE than French colleagues are.Comparing our results with those from Torres-Unda et al. ( 2013), it could be said there are certain differences.While present study did not show statistically signifi cant differences in most of measures and abilities, analysis of Spanish authors showed that elite selected basketball players, aged 13 and 14, better in all measured and tested dimensions than their non-elite peers where.Young elite basketball players where taller, heavier, more muscular, faster on 20 meters, better in jumping, endurance and agility.Most of elite players were born in the fi rst half of the year.Thus, presence of RAE among their subjects is evident.The differences in relation to our study probably come from the fact that our subjects are part of two best teams, and their subjects are part of two different quality ranks: elite and non-elite.
It is interesting to compare RAE analysis in sports where body height is not that important like it is in basketball.Results from authors who examined relation of RAE and anthropometric, motor and physiological indicators on population of young football players are in line with existence of differences between pubertal boys born in the fi rst and second half of the year.In S. Gil, Ruiz, A. Irazusta, J. Gil, and J. Irazusta (2007) study, most of the selected 14-yearold boys were born in the fi rst half of the year.Moreover, older 14-year-old boys were taller, faster and more agile.They had bigger absolute and relative oxygen consumption.Authors claim that older peers are more frequent in senior category.Similar results where obtained on population of young football players (Musch, & Hay, 1999 (2008) found that for school teams (football, rugby and netball) there is a higher percent of children who were born in the fi rst part of the year.

CONCLUSION
Coaches of teams that participated in the present study did not make discrimination in the selec-more, it would be interesting to compare RAE of young Serbian basketball players with RAE of players from other countries, applying measurements nad tests from our study.Third recommendation could be to consider and examine biological age (maturity) of young basketball players.
The results of this study could have practical application in training of younger basketball player categories.Recommendation for coaches is to take in consideration dangers and traps of RAE.Particular effort should be invested in motivating young players, who were born in the second half of the year, not just to stay in basketball, but to train hard and regularly.
tion process during their work in the past.Privileging of children born in the fi rst half of the year has not been noted in this study.There was not reason for that either, because younger players did not signifi cantly trail older players in measured and tested variables.It is quite possible that younger group has few accelerants, which makes these two groups almost equal in measured characteristics and abilities.Second possibility refers to potential genetic predisposition for playing basketball in members of the younger group.With respect to that, small sample of subjects could be limitation of this study.Obviously, it would be usefull to apply all these measures and tests on larger population of young basketball players.Herewith, reliability of conclusion would be greater.Further-

Table 1 .
Descriptive statistics and differences between the groups

Table 2 .
Some physical characteristics and abilities of primary school children from different countries