José Antonio Lekue

Relationship between the relative age effect and anthropometry, maturity and performance in young soccer players

Abstract The presence of the relative age effect (RAE) has been widely reported; however, its underlying causes have not yet been determined. With this in mind, the present study examined if anthropometry and performance were different amongst older and younger soccer players born in the same year. Eighty-eight young soccer players participated in the study (age 9.75 ± 0.30). Anthropometric measurements, physical tests (sprint, agility, endurance test, jump and hand dynamometry) and the estimation of the maturity status were carried out. Most players (65.9%) were born in the first half of the year. Older players were taller (P < 0.05), had longer legs (P < 0.01) and a larger fat-free mass (P < 0.05). Maturity offset was smaller in the older boys (P < 0.05); however, age at peak height velocity was similar. Older boys performed better in velocity and agility (P < 0.05) and particularly in the overall score of performance (P < 0.01). Stepwise regression analysis revealed that chronological age was the most important variable in the agility test and the overall score, after the skinfolds (negative effect). We report differences in anthropometry and physical performance amongst older and younger pre-pubertal soccer players. These differences may underlie the RAE.

Influence of nutrient intake on antioxidant capacity, muscle damage and white blood cell count in female soccer players.

BackgroundSoccer is a form of exercise that induces inflammatory response, as well as an increase in free radicals potentially leading to muscle injury. Balanced nutritional intake provides important antioxidant vitamins, including vitamins A, C and E, which may assist in preventing exercise-related muscle damage. The purpose of the present study was to determine the effect of macro/micronutrient intake on markers of oxidative stress, muscle damage, inflammatory and immune response in female soccer players.MethodsTwenty-eight female players belonging to two soccer teams of the same professional soccer club participated in this study after being informed about the aims and procedures and after delivering written consent. Each team completed an 8-day dietary record and played one competition match the same week. Participants were divided into two groups: the REC group (who complied with recommended intakes) and the NO-REC group (who were not compliant). Laboratory blood tests were carried out to determine hematological, electrolytic and hormonal variables, as well as to monitor markers of cell damage and oxidative stress. Blood samples were obtained 24 h before, immediately after and 18 h after official soccer matches. Student t-test or Mann–Whitney U-test was used to compare both groups throughout the match.ResultsAt rest, we observed that the REC group had higher levels of total antioxidant status (TAS), glutathione peroxidase (GPx), and lower levels of creatine kinase (CK) and lactate dehydrogenase (LDH) in comparison to the NO-REC group. Immediately after the match, levels of TAS, GPx, superoxide dismutase (SOD), LDH and % lymphocytes were higher and the % of neutrophils were lower in the REC group compared to the NO-REC group. These differences were also maintained 18 h post-match, only for TAS and GPx.ConclusionsOur data reveal an association between nutritional intake and muscle damage, oxidative stress, immunity and inflammation markers. The benefit of the intake of specific nutrients may contribute to preventing the undesirable physiological effects provoked by soccer matches.

Talent identification and selection process of outfield players and goalkeepers in a professional soccer club

Abstract The aim of this study was to analyse the talent identification process of a professional soccer club. A preselection of players (n = 64) aged 9–10 years and a final selection (n = 21) were performed by the technical staff through the observation during training sessions and matches. Also, 34 age-matched players of an open soccer camp (CampP) acted as controls. All participants underwent anthropometric, maturity and performance measurements. Preselected outfield players (OFs) were older and leaner than CampP (P < 0.05). Besides, they performed better in velocity, agility, endurance and jump tests (P < 0.05). A discriminant analysis showed that velocity and agility were the most important parameters. Finally, selected OFs were older and displayed better agility and endurance compared to the nonselected OFs (P < 0.05). Goalkeepers (GKs) were taller and heavier and had more body fat than OFs; also, they performed worse in the physical tests (P < 0.05). Finally, selected GKs were older and taller, had a higher predicted height and advanced maturity and performed better in the handgrip (dynamometry) and jump tests (P < 0.05). Thus, the technical staff selected OFs with a particular anthropometry and best performance, particularly agility and endurance, while GKs had a different profile. Moreover, chronological age had an important role in the whole selection process.

Metabolic impact of a soccer match on female players.

Abstract The aim of this study was to examine the metabolic effect of a female soccer match in elite and sub-elite teams. Blood samples were taken (24 h before, immediately after and 18 h after official soccer matches) to determine haematological, electrolytic and hormonal variables, as well as the levels of cell damage and oxidative stress in 14 elite and 14 sub-elite players. Our results show increases in white blood cell count (P < 0.001) and the percentage of neutrophils (P < 0.001), and decreases in the percentage of lymphocytes (P < 0.05), eosinophils (P < 0.001), monocytes (P < 0.001) and basophils (P < 0.05) immediately post-match. Increases were also found in lactate dehydrogenase activity (P < 0.001), uric acid (P < 0.001), albumin (P < 0.001), total antioxidant status (P < 0.001) and free testosterone levels (P < 0.01). Creatine kinase activity significantly increased 18 h post-match (P < 0.01) and the concentrations of several ions, glucose and proteins were found to be altered immediately post-match. Overall, our results show that playing a soccer match exerts specific metabolic effects on female players, resulting in muscle damage, oxidative stress and biochemical and hormonal variations. On the basis of some interesting correlations, we also suggest that exercise-induced cell breakdown may enhance antioxidant capacity of the soccer players.

Physical growth and changes in intermittent endurance run performance in young male Basque soccer players.

The present 4-year longitudinal study examined physical growth and development of intermittent endurance run performance in young Basque soccer players aged 10–15 years applying multilevel regression modeling. Anthropometry, predicted adult stature and Yo-Yo Intermittent Recovery level 1 test (Yo-Yo IR1) of players from the under-11 teams from the Athletic Club of Bilbao were measured at pre- and end-season (two measurements per year of study, n = 33 considered for analysis). A non-linear effect of age on intermittent endurance run was observed, with significantly higher increases in Yo-Yo IR1 between 10–11 year-old and 14–15 year-old players. The development of Yo-Yo IR1 performance in all the years of the study was influenced positively by training exposure during the seasons (P < 0.01) and independent of maturity status and body size (P > 0.05). The steady development of intermittent endurance run performance during pubertal years in adolescent Basque soccer players is partially influenced by training exposure.

A comparison of injuries in elite male and female football players: A five-season prospective study

The aim was to compare the epidemiology of injuries between elite male and female football players from the same club. Injuries and individual exposure time in a male team and a female team, both playing in the Spanish first division, were prospectively recorded by the clubs medical staff for five seasons (2010‐2015) following the FIFA consensus statement. Total, training, and match exposure hours per player‐season were 20% higher for men compared to women (P<.01). Total, training, and match injury incidence were 30%‐40% higher in men (P≤.04) mainly due to a 4.82 (95% confidence interval [CI] 2.30‐10.08) times higher incidence of contusions, as there were no differences in the incidence of muscle and joint/ligament injuries (P≥.44). The total number of absence days was 21% larger in women owing to a 5.36 (95% CI 1.11‐25.79) times higher incidence of severe knee and ankle ligament injuries. Hamstring strains and pubalgia cases were 1.93 (95% CI 1.16‐3.20) and 11.10 (95% CI 1.48‐83.44) times more frequent in men, respectively; whereas quadriceps strains, anterior cruciate ligament ruptures, and ankle syndesmosis injuries were 2.25 (95% CI 1.22‐4.17), 4.59 (95% CI 0.93‐22.76), and 5.36 (95% CI 1.11‐25.79) times more common in women, respectively. In conclusion, prevention strategies should be tailored to the needs of male and female football players, with men more predisposed to hamstring strains and hip/groin injuries, and women to quadriceps strains and severe knee and ankle ligament injuries.

Applicability of an agility test in young players in the soccer field

Introduction: in soccer, agility is a relevant parameter that is defined as the ability to change the direction of the body rapidly and is a result of a combination of strength, speed, balance and coordination. Objective: to demonstrated the reliability and validity of the modified Barrow test in soccer players aged 10 to 14 years, analyze its relationship with age, maturation, experience and body size and test the effectiveness of the protocol for distinguishing performance changes during a 10-month competitive season. Methods: fifty-one adolescent Basque soccer players were enrolled. Age, maturation, experience, body size, vertical jump and 15-m sprint were measured. The reliability of the test was analyzed using replicate tests in a subgroup (n = 34). Another subgroup of 33 players (n =18, under-11, 10.4 ± 0.3 years; n = 15 under-13, 12.0 ± 0.8 years) was evaluated at the beginning and the end of the season. Results: the reliability of the test was good (change in mean = -0.5%, 95% CI -1.2 to 0.2, SD=0.14; coefficient of variation = 0.9%, 95% CI - 0.7 to 1.5, SD=0.25). Chronological age and adiposity were significant predictors of agility performance (P<0.01). An improvement in performance was observed over a 10-month soccer season, with a significant group effect (P<0.01). Conclusion: the agility test demonstrated logic and validity, and proved to be a reliable and objective instrument for assessing adolescent soccer players.INTRODUCCION: en futbol, la agilidad es un parametro relevante. Asi, este parametro esta definido como la capacidad para cambiar de direcciones de forma rapida y es el resultado de una combinacion de fuerza, velocidad, equilibrio y coordinacion.OBJETIVO: demostrar la validez y confiabilidad del test modificado de Barrow en jovenes jugadores de futbol de 10 a 14 anos, analizar la relacion con la edad, maduracion, experiencia y tamano corporal y comprobar la efectividad del protocolo para distinguir cambios de rendimiento durante una temporada competitiva de 10 meses.METODOS: participaron 55 jugadores adolescentes vascos. Se realizaron las siguientes mediciones: edad, maduracion, experiencia, composicion corporal, salto vertical y sprint de 15 metros. La confiabilidad del test fue analizada mediante test replicado en un subgrupo de 34 jugadores. Otro subgrupo de 33 jugadores n = 18 sub-11, 10,4 ± 0,3 anos; n = 15 sub-13, 12,0 ± 0,8 anos fue analizado al principio y al final de la temporada.RESULTADOS: la confiabilidad del test fue buena cambios en la media = -0,5%, 95% IC - 1,2 a 0,2, ES-d = 0,14; el coeficiente de variacion fue 0,9%, 95% IC - 0,7 a 1,5, ES-d = 0,25. La edad cronologica y la adiposidad fueron predictores del rendimiento de la agilidad P < 0,01. Se observo una mejora importante del rendimiento durante los 10 meses de temporada con un efecto de grupo significativo P < 0,01.CONCLUSION: el test de agilidad demostro logica y validez ademas de ser un instrumento confiable y objetivo para evaluar la agilidad en jugadores de futbol adolescentes.

Longitudinal field test assessment in a Basque soccer youth academy: a multilevel modeling framework to partition effects of maturation.

The purpose of the study was to examine the effect of age on short-term performance indicators applying multilevel regression modeling, and whether changes induced by age were affected by maturation. The study applied a mixed longitudinal approach with 8 measurement points over a period of 4 years. Anthropometry, predicted adult stature, countermovement jump, 15-m sprint and agility test from 38 under-11 young soccer players were considered. Early maturing players were 3% taller compared to late maturers. A substantial effect of age was present in all performance indicators (P<0.05). Parameters showed improvements in performance, even when accounting for interindividual variation in somatic maturity. Vertical jump tended to be stable in early maturers during the first year, presenting an exponential increase thereafter (16%, P<0.05). Additionally, early maturing boys had lower vertical jump scores but a substantial higher rate of development with age (3% per year). Performance tends to plateau during the first 3 years following the improvements in agility (9.1%, P<0.05). In the running tests, early maturers had better performances (19%, P<0.05), while a higher rate of improvement of 1% was observed for the late maturers. Young soccer players should be expected to have substantial improvements in short-term performance, influenced by independent variation between players in maturity status.

Pubertal development of body size and soccer-specific functional capacities in adolescent players

ABSTRACT Pubertal growth in body size and functional capacities were examined in adolescent soccer players (n = 33). The average age at baseline was 10.9 (9.8–11.8 years). Peak height velocity (PHV) and growth curves for body mass and functional performance (countermovement jump, 15-m sprint, agility and Yo-Yo intermittent recovery test – level 1) were determined with Bayesian multilevel models. Estimates for PHV and age at PHV were 8.1 cm/year (95% credible interval: 4.2–18.5 cm/year) and 12.9 years (95% credible interval: 11.8–15.5 years), respectively. Peak body mass velocity occurred 0.48 year after PHV. Jump performance maximum velocity occurred about 2 years after PHV and peak sprint performance maximum velocity was coincident with PHV. Agility and intermittent endurance run performance showed a quadratic trend of improvement of performance, starting to level off at about 3–4 years after PHV. The modelling procedures were efficient to determine pubertal growth curves aligned for chronological age and age at PHV, considering individual differences in maturation when interpreting the development of performance in youth soccer.