V MOTOR ABILITIES AND RELATIVE AGE EFFECT OF ADOLESCENTS

The present study examined the relative age effects (RAE) of adolescents from Bosnia and Herzegovina. The purposes of this study were to evaluate motor performances of adolescent students (boys and girls), and to examine the effects of relative age among relatively older and relatively younger boys, and between relatively older and relatively younger girls, respectively. Motor skills were assessed by the Eurofit battery of motor tests. A one-way analysis of variance (ANOVA) was applied to examine the differences between the groups. Normality of distribution was determined with Kolmogorov-Smirnov test and skewness and kurtosis. If the assumption of a normal distribution for the data was violated, the Mann–Whitney U test. The results indicated significant differences in motor performance boys RAE groups in two measures, while there were no differences between the relatively older and relatively younger girls. The results indicate that the RAE is less evident in mid-adolescence in both, girls and boys. These findings may be useful for physical education (PE) teachers in PE lessons planning.


INTRODUCTION
Relative age effect (RAE) has caught attention to the researchers in sport domain for over 30 years.Barnsley et al. (1985) found that approximately 40% of young athletes participating in the major Canadian amateur ice hockey leagues (the Western and Ontario Hockey League) were born in the first three months (January-March) of the annual age group, while only 10% of athletes were born in the last three months (October-December).Over the years, these effects have been observed in a number of sports: tennis, rugby, football, baseball (Cobley et al., 2009).The advantages that relatively older youth are experiencing more likely originate from differences in physical size and maturation (Wattie et al., 2014).
Moreover, researchers have observed RAEs in physical education (Bell, et al., 1997;Cobley, et al., 2008) and other educational domains (McPhillips and Jordan-Black, 2009).One of the most recent studies (Nakata et al., 2017) investigated characteris-process in 13-year-old basketball players where authors did not identify significant RAEs between the two group of players possibly due to the small number of participants (n=20) (Vučković et al., 2013).
In more recent study, with primary school pupils as a sample (13-year-old pupils), authors found that significant RAEs exist in physical, as well as in motor variables, in both boys and girls (Gadžić et al., 2017).Intention of the authors of current study was to further explore this phenomenon in 15-year-old pupils from Bosnia and Herzegovina.In Bosnia and Herzegovina educational system, annual age grouping policy currently runs from January 1 st to December 31 st of the same year.This means that a child born on January 1 st would be almost a year older than a child born in December of the same year.
The purposes of this study were: (a) to evaluate motor performances of 15-year-old boys and girls from Bosnia and Herzegovina and (b) to examine the RAEs among relatively older and relatively younger boys (ROB and RYB), and between relatively older and relatively younger girls (ROG and RYG) respectively.
Having in mind that earlier studies of RAEs mainly covered preadolescent pupils, we wanted to explore the impact of RAEs in Bosnian adolescents.Considering that previous studies confirmed that relatively older students have better results on motor abilities tests, the authors of present study expected to find similar differences in current sample.

Sample
The total sample consisted of 227 apparently healthy 15-years-old students, 129 females and 98 males from two secondary schools in Banja Luka.The mean age for boys sample was 15.33 years (SD = 0.49 ).The mean height was 179.48 cm (SD = 0.07) and mean body mass was 69.18 kg (SD = 13.24).The mean age for girls sample was 15.34 years (SD = 0.48 ).The mean height was 169.26 cm (SD = 0.06) and mean body mass was 62.09 kg (SD = 10.07).Considering the annual age grouping policy in Bosnia and Herzegovina educational system, which currently runs from January 1 st to December 31 st of the same year, the participants were grouped in relatively younger and relatively older students.They were grouped by month of birth in two groups (Group 1: January-June 2002, n = 145; Group 2: July-December 2002, n = 82).Groups were furtherly divided gendervise into four groups: a group of relatively older boys (ROB, n = 60), a group of relatively younger boys (RYB, n = 38), a group of relatively older girls (ROG, n = 85), and a group of relatively younger girls (RYG, n = 44).

Measures
Participants' motor skills were assessed by the selected tests from the Eurofit battery of motor tests (Eurofit, 1993) The Eurofit was chosen since it has become the most popular test battery used to assess the physical fitness of European children and adolescents and the effectiveness of national physical education curricula (Kemper and Van Mechelen, 1996;Tomkinson et al., 2007).Each test has specific instructions that need careful study and had to be read to each pupil in order to make the testing as objective as possible.The pupils were required to remain at rest between each test and they were not allowed to have a preliminary trial of the test unless this is explicitly stated in the test instructions.It was important to encourage the pupils during the testing.The standardised tests were conducted by experienced physical education teachers and the sequence of motor tests was organized in a circuit system with a strict testing order.Hand grip test (HGR) was measured by isometric dynamometer Uno Lux (Serbia).
Apart from the motor skill measures, following basic anthropometric measures were taken as well: body weight (BW), body height (BH), and body mass index (BMI).Following variables were taken as categorical ones: Relatively older boys (ROB), Relatively younger boys (RYB), Relatively older girls (ROG), and Relatively younger girls (RYG).are shown as p<.05 and p<.01.All statistical analyses were conducted using SPSS software version 21.0 (SPSS Inc, Chicago, IL).

Descriptive statistics
Initial analysis of normality (Kolmogorov-Smirnov) indicated that both boys groups had a normal distribution in five motor tests (except in shuttle run test 10x5m, hand grip test and Flamingo balance test).

Data Analysis
Descriptive statistics for body mass, height, BMI and all motor variables were calculated.All participants were separated by sex and relative age group (relatively older and relatively younger) and assigned to one of four groups: relatively older boys in group one, relatively younger boys in group two, relatively older girls in group three, and relatively younger girls in group four.A one-way analysis of variance (ANO-VA) was applied to examine the differences between the groups.Normality of distribution was determined with Kolmogorov-Smirnov test and skewness and kurtosis.If the assumption of a normal distribution for the data was violated, the Mann-Whitney U test.Significance was set at p<.05, and the p values  Note: Mean = arithmetic mean; SD = standard deviation; K-S = Kolmogorov-Smirnov test; Skew = Skewness; Kurt = Kurtosis However, in girls (Table 2.) initial normality could be seen only in three out of eight motor tests (sit-ups, plate tapping and sit and reach).Following the previously mentioned rationale suggested by Kim (2013) and West et al. (1995), further investigation of skewness and kurtosis values indicated rather normal distribution except for the bent arm hang test, where Mann-Whitney U test was applied.

Differences between RAE groups
A one-way analysis of variance (ANOVA) and Mann-Whitney U test were applied to examine the differences between the relatively older (group 1) and relatively younger (group 2) pupils.Among girls subsample, we did not find significant differences in any of eight motor performance tests, between the relatively older and relatively younger girls.

DISCUSSION
The first purpose of this study was to evaluate the motor performances of 15-year-old boys and girls from Bosnia and Herzegovina.We performed a comparison of the results in motor performance tests with European normative values for physical fitness in children and adolescents aged 9-17 years from Eurofit performances in 30 countries (Tomkinson et al., 2017a).Several authors (Tomkinson et al., 2017b; The results presented in Table 3. show motor performance indicators for the two groups of boys, relatively older and relatively younger boys.Mann-Whitney U test revealed significant RAE difference between the groups, where relatively younger boys (born July-December) had better results in plate tapping test (p < .05).Conversely, relatively older boys showed better results in sit and reach test ( p < .04).However, there were no other significant differences between the groups in the remaining motor performance tests (shuttle run, bent arm hang, sit-ups for 30 sec, standing broad jump, hand grip and Flamingo balance).).In the Plate tapping test, the results could be classified as poor (below 40 th centile), while the results in Sit and reach test (M = 30.27;SD = 8.29) can be classified as very high (above the 80 th centile).The last test, Flamingo balance results (M = 6.59;SD = 3.72) fits in 60-80 th centiles, or 'high/good' category.
Among 15-year-old girls, the results for the Shuttle run test (M = 20.07;SD = 3.82) were above the 80th centile or 'very high/good' .Girls showed good correspondence with the European normative values in the Bent arm hang test with the results (M = 9.36; SD = 9.47) above the 70 th centile.In Sit-ups test and Standing broad jump test (M = 20.34;SD = 3.99; M = 157.28;SD = 0.24, respectively), 15-year-old girls from Bosnia and Herzegovina had moderate results (between 40-60 th centiles of European normative values).Almost identically to the boys, the least correspondence (below 20th centile, or very poor) with the European normative values was noted in Hand grip test (M = 21.94;SD = 9.34).In the Plate tapping test, the girls' results (M = 11.93;SD = 1.48) could be classified as moderate (between 40 th -60 th centile).The results in Sit and reach test (M = 35.88;SD = 7.35) can be classified as very high (above the 80 th centile), and the last test, Flamingo balance (M = 6.26;SD = 4.32) fits in 60-80 th centiles, or 'high/good' category.
Considering all of above mentioned results, it is interesting to note that the only test where both, boys and girls from Bosnia and Herzegovina had very low results in comparison with the European normative values for physical fitness in children and adolescents, was Hand grip test (static arm strength).This inconsistency may be explained with possible use of different dynamometers.The results of the current study showed some influence of relative age on motor performance variables among boys RAE groups.A significant differences were revealed with relatively younger boys (born July-December), who had better results in plate tapping test and relatively older boys showed better results in sit and reach test, respectively.These findings are very consistent with the most recent study conducted on the large sample (Nakata et al., 2017) wich showed a significant relative age effects in two measures only (hand grip and sit and reach), where 15-year-old, relatively older boys, had better results.Interestingly, the results of that study identified more RAE differences from the age 11 to 14 years than at the age of 15.The differences were noted at least in four measures, and at the age of 14 years, there were six out of seven measures in favour of relatively older boys.In previous study (Gadžić et al., 2017), similar results were obtained in 12-year-old pupils (relatively older boys had better results in five out of eight measures).This may indicate that the RAE is less evident as adolescents age.
Considering the girls subsample, no significant differences in any of eight motor performance tests were found, between the relatively older and relatively younger girls.In a recent study (Gadžić et al., 2017), same motor performance test (Eurofit) was applied on the 12-year-old girls, more differences between the RAE groups of girls were found, where relatively older girls had outperformed their relatively younger classmates in six out of eight motor tests (static strength, balance, the speed of limb movement, flexibility, abdominal muscular endurance, and arm and shoulder muscular endurance, respectively).Similar to Nakata et al. (2017), this study did not find significant RAE in motor performance tests in 15-year-old girls, confirming their findings that RAE is more evident for boys than girls in adolescence.

CONCLUSION
Although, there is a limited number of studies on the RAE in general population during adolescence, the results from the most recent study conducted by Nakata et al. (2017) and the current study clearly indicate that the RAE is less evident in mid-adolescence in both, boys and girls.Aparently, early adolescence is a period of intensive growth when maturation variability is the greatest (Musch and Grondin, 2001).One-year age differences, especially during the stages of puberty (i.e., 13-15 years of age in boys; 12-14 years in girls) can heighten physical (Baxter-Jones et al., 1994; Baxter-Jones et al., 1995) and performance differences (Levfvre et al., 1990;Malina et al., 2007).Note that an undefined number of these adolescents engage in some sporting activities.
These findings may be useful for PE teachers in PE assessment and lessons planning.Limitations of the present study may be relatively small sample, which is drawn from only two schools and is not large enough for generalization.Second, we did not identify PA level of the participants, nor their maturity.Future research should examine the RAE on larger general sample of adolescents in physical education context, in order to definitely confirm decrease of the RAE during mid-adolescence.

Table 1 .
Descriptive statistics for boys

Table 2 .
Descriptive statistics for girls

Table 4 .
Difference of motor performance in girls

Table 3 .
Difference of motor performance in boys Note: Mean = arithmetic mean; SD = standard deviation; Sig = level of statistical significance