Anthropometrical, physical fitness and maturational characteristics in youth soccer : methodological issues and a longitudinal approach to talent identification and development

From the literature, it has been massively recommended that talent identification, development and selection processes in youth soccer should provide a longitudinal, holistic approach accounting for maturation and relative age. The sport of soccer systematically excludes those players who are later to mature and/or who are later born in the in the selection year, whilst these players might be as gifted as their earlier maturing and/or earlier born peers. There are often no or insufficient objective criteria that could support the evaluation process. The present thesis aimed to gain insight in young soccer players’ development of anthropometrical characteristics, physical fitness and motor coordination parameters with respect to maturation and relative age. Therefore, the conducted research was divided into four different chapters. The first chapter investigated (1) test-retest reliability and validity of the intermittent endurance performance, assessed by the Yo-Yo Intermittent Recovery test level 1 (YYIR1) in elite, suband non-elite players (study 1, n=228, 10-17 y; study 2, n=36, 13-18 y ), (2) the short- and long-term stability of anthropometrical characteristics and YYIR1 of 42 pubertal soccer players (study 3), and (3) the relationship between invasive (skeletal age) and non-invasive (estimation of age at peak height velocity) protocols to estimate adult stature on the one hand, and the agreement between methods assigning players to somatic maturity categories on the other in a mixed-sample of 160 Belgian and Brazilian elite players (study 4). Combining the results of the first two studies, the YYIR1 seems more reliable at elite level and at older ages (U17-U19) compared with sub-/non-elite level and at younger ages (U13-U15). Also, players with a relatively low YYIR1 performance at the age of 12 years are able to (however partially) catch-up the better performers over a four-year period, suggesting the need for individualization within the training process (study 3). Furthermore, the fourth study demonstrated that invasive and non-invasive protocols correspond well in estimating mature stature, although transforming estimated APHV into somatic maturity categories has proven to be problematic in elite youth soccer players. The second chapter focused on the influence of relative age on both aerobic (YYIR1) (study 5, n=606, U10-U19) and anaerobic performance measures (speed and explosive leg power) (study 6, n=374, U13-U17). A clear overrepresentation of players born in the first part of the selection year was found in both studies, although relative age did not confound aerobic as well as anaerobic performance measures. This might be explained by the fact that (1) the formation of homogenous players in terms of aerobic and anaerobic performances was already manifest before the age of 10 years, and (2) this reflects the variation in maturity status among players within the same age-cohort. The third chapter investigated the longitudinal development of the YYIR1 performance (study 7, n=162, 11-14 y) and explosive leg power (study 8, n=356, 11-14 y; study 9, n=555, 7-20 y) via multilevel analyses. Also, retrospective data were used to predict drop out, contract status and first-team playing time using anthropometrical, maturational, physical fitness and motor coordination characteristics (study 10, n=388, 8-16 y). Generally, the results highlighted that non-specific motor coordination contributed significantly to the development of aerobic and anaerobic performances, and that this parameter could distinguish between future successful and less successful young soccer players. Further, young soccer players possessing higher levels of explosive leg power from the age of 16 years are more likely to sign a professional contract and are receiving more playing minutes at the professional adult level. The final chapter described differences in 744 youth soccer players’ (9 to 18 y) anthropometrical characteristics and general fitness level through aerobic and anaerobic tests according to the playing position on the field (study 11). The results revealed that inherent anthropometrical and physical capacities (i.e., speed, power, agility) might select players in or reject players from certain positions, and the time around peak height velocity seems to be crucial in this selection process. However, the typical characteristics for the different playing positions at senior level are yet not fully developed among young soccer players between 8 and 14 years, although the typical anthropometrical characteristics of goalkeepers (i.e., taller and heavier) were already manifest at young age. In conclusion, the abovementioned studies in this thesis (1) emphasize the use of the YYIR1 as a valid, reliable and maturity-independent tool to assess a players’ intermittent endurance capacity, (2) highlight that the selection process is focused on the formation of homogenous groups of players in terms of anthropometrical, maturational and physical fitness parameters, independent of playing position, and (3) that non-specific motor coordination is essential in the development of physical fitness measures and should be included in the training process

Tanner-Whitehouse skeletal ages in male youth soccer players : TW2 or TW3?

BACKGROUND: The Tanner-Whitehouse radius-ulna-short bone protocol (TW2 RUS) for the assessment of skeletal age (SA) is widely used to estimate the biological (skeletal) maturity status of children and adolescents. The scale for converting TW RUS ratings to an SA has been revised (TW3 RUS) and has implications for studies of youth athletes in age-group sports. OBJECTIVES: The aim of this study was to compare TW2 and TW3 RUS SAs in an international sample of male youth soccer players and to compare distributions of players by maturity status defined by each SA protocol. METHODS: SA assessments with the TW RUS method were collated for 1831 male soccer players aged 11-17 years from eight countries. RUS scores were converted to TW2 and TW3 SAs using the appropriate tables. SAs were related to chronological age (CA) in individual athletes and compared by CA groups. The difference of SA minus CA with TW2 SA and with TW3 SA was used to classify players as late, average, or early maturing with each method. Concordance of maturity classifications was evaluated with Cohen's Kappa coefficients. RESULTS: For the same RUS score, TW3 SAs were systematically and substantially reduced compared with TW2 SAs; mean differences by CA group ranged from - 0.97 to - 1.16 years. Kappa coefficients indicated at best fair concordance of TW2 and TW3 maturity classifications. Across the age range, 42% of players classified as average with TW2 SA were classified as late with TW3 SA, and 64% of players classified as early with TW2 SA were classified as average with TW3 SA. CONCLUSION: TW3 SAs were systematically lower than corresponding TW2 SAs in male youth soccer players. The differences between scales have major implications for the classification of players by maturity status, which is central to some talent development programs

16p11.2 600 kb Duplications confer risk for typical and atypical Rolandic epilepsy

Rolandic epilepsy (RE) is the most common idiopathic focal childhood epilepsy. Its molecular basis is largely unknown and a complex genetic etiology is assumed in the majority of affected individuals. The present study tested whether six large recurrent copy number variants at 1q21, 15q11.2, 15q13.3, 16p11.2, 16p13.11 and 22q11.2 previously associated with neurodevelopmental disorders also increase risk of RE. Our association analyses revealed a significant excess of the 600 kb genomic duplication at the 16p11.2 locus (chr16: 29.5-30.1 Mb) in 393 unrelated patients with typical (n = 339) and atypical (ARE; n = 54) RE compared with the prevalence in 65 046 European population controls (5/393 cases versus 32/65 046 controls; Fisher's exact test P = 2.83 × 10−6, odds ratio = 26.2, 95% confidence interval: 7.9-68.2). In contrast, the 16p11.2 duplication was not detected in 1738 European epilepsy patients with either temporal lobe epilepsy (n = 330) and genetic generalized epilepsies (n = 1408), suggesting a selective enrichment of the 16p11.2 duplication in idiopathic focal childhood epilepsies (Fisher's exact test P = 2.1 × 10−4). In a subsequent screen among children carrying the 16p11.2 600 kb rearrangement we identified three patients with RE-spectrum epilepsies in 117 duplication carriers (2.6%) but none in 202 carriers of the reciprocal deletion. Our results suggest that the 16p11.2 duplication represents a significant genetic risk factor for typical and atypical R

Running economy in elite soccer and basketball players : differences among positions on the field

In the present study running economy (RE) was recorded in elite soccer and basketball players and positional differences were addressed. Elite soccer players (n = 111) and basketball players (n = 39), active in the Belgian first division performed an incremental running test (8 km. h(-1) + 2 km. h(-1) each three minutes) on a treadmill until exhaustion. Throughout the test gas exchange was registered and capillary blood samples were taken from which peak oxygen uptake (VO2 peak), speed at the anaerobic threshold (V-AnT) and RE could be determined. These parameters were compared among the playing positions in soccer and basketball. In soccer, midfielders (214.4 +/- 11.1 ml. km(-1). kg(-1)) and full-backs (218.4 +/- 10.3 ml. km(-1). kg(-1)) had a significantly higher RE compared to center-backs (231.4 +/- 8.8 ml. km(-1). kg(-1)). In basketball, guards (229.4 +/- 10.4 ml. km(-1). kg(-1)) had a significantly higher RE compared to forwards (237.8 +/- 9.3 ml. km(-1). kg(-1)) and centers (243.3 +/- 13.2 ml. km(-1). kg(-1)). These differences in RE were accompanied by similar positional differences in VO2 peak and VAnT. Furthermore, both in soccer (R = 0.56) and basketball (R = 0.63), RE was correlated to VAnT. The present study points at the importance of RE in physical preparation of team sports and it can be concluded that teamsport-specific training should also focus on improving RE

Relative age effect and Yo-Yo IR1 in youth soccer

The aims of the study were to investigate the presence of a relative age effect and the influence of birth quarter on anthropometric characteristics, an estimation of biological maturity and performance in the Yo-Yo Intermittent Recovery Test level 1 in 606 elite, Flemish youth soccer players. The sample was divided into 5 chronological age groups (U10-U19), each subdivided into 4 birth quarters. Players had their APHV estimated and height, weight and Yo-Yo IR1 performance were assessed. Differences between quarters were investigated using uni- and multivariate analyses. Overall, significantly (P<0.001) more players were born in the first quarter (37.6%) compared to the last (13.2%). Further, no significant differences in anthropometric variables and Yo-Yo IR1 performance were found between the 4 birth quarters. However, there was a trend for players born in the first quarter being taller and heavier than players born in the fourth quarter. Players born in the last quarter tended to experience their peak in growth earlier, this may have enabled them to compete physically with their relatively older peers. Our results indicated selection procedures which are focused on the formation of strong physical and physiological homogeneous groups. Relative age and individual biological maturation should be considered when selecting adolescent soccer players

A retrospective study on anthropometrical, physical fitness, and motor coordination characteristics that influence dropout, contract status, and first-team playing time in high-level soccer players aged eight to eighteen years

The goal of this article was twofold, and a 2-study approach was conducted. The first study aimed to expose the anthropometrical, physical performance, and motor coordination characteristics that influence dropout from a high-level soccer training program in players aged 8-16 years. The mixed-longitudinal sample included 388 Belgian youth soccer players who were assigned to either a "club group" or a "dropout group." In the second study, cross-sectional data of anthropometry, physical performance, and motor coordination were retrospectively explored to investigate which characteristics influence future contract status (contract vs. no contract group) and first-team playing time for 72 high-level youth soccer players (mean age = 16.2 years). Generally, club players outperformed their dropout peers for motor coordination, soccer-specific aerobic endurance, and speed. Anthropometry and estimated maturity status did not discriminate between club and dropout players. Contract players jumped further (p = 0.011) and had faster times for a 5-m sprint (p = 0.041) than no contract players. The following prediction equation explains 16.7% of the variance in future playing minutes in adolescent youth male soccer players: 22,869.3 + 14.6 x standing broad jump. Practitioners should include the evaluation of motor coordination, aerobic endurance, and speed performances to distinguish high-level soccer players further succeeding a talent development program and future dropout players, between 8 and 16 years. From the age of 16 years, measures of explosivity are supportive when selecting players into a future professional soccer career

The Yo-Yo intermittent recovery test level 1 is reliable in young high-level soccer players

The aim of the study was to investigate test reliability of the Yo-Yo intermittent recovery test level 1 (YYIR1) in 36 high-level youth soccer players, aged between 13 and 18 years. Players were divided into three age groups (U15, U17 and U19) and completed three YYIR1 in three consecutive weeks. Pairwise comparisons were used to investigate test reliability (for distances and heart rate responses) using technical error (TE), coefficient of variation (CV), intra-class correlation (ICC) and limits of agreement (LOA) with Bland-Altman plots. The mean YYIR1 distances for the U15, U17 and U19 groups were 2024 ± 470 m, 2404 ± 347 m and 2547 ± 337 m, respectively. The results revealed that the TEs varied between 74 and 172 m, CVs between 3.0 and 7.5%, and ICCs between 0.87 and 0.95 across all age groups for the YYIR1 distance. For heart rate responses, the TEs varied between 1 and 6 bpm, CVs between 0.7 and 4.8%, and ICCs between 0.73 and 0.97. The small ratio LOA revealed that any two YYIR1 performances in one week will not differ by more than 9 to 28% due to measurement error. In summary, the YYIR1 performance and the physiological responses have proven to be highly reliable in a sample of Belgian high-level youth soccer players, aged between 13 and 18 years. The demonstrated high level of intermittent endurance capacity in all age groups may be used for comparison of other prospective young soccer players

Lightning related fatalities in livestock: veterinary expertise and the added value of lightning location data

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