Background Skeletal age (SA) is an estimate of biological maturity status that is commonly used in sport-related medical examinations. This study considered intra-observer reproducibility and inter-observer agreement of SA assessments among male tennis players. Methods SA was assessed with the Fels method in 97 male tennis players with chronological ages (CA) spanning 8.7–16.8 years. Radiographs were evaluated by two independent trained observers. Based on the difference between SA and CA, players were classified as late, average or early maturing; if a player was skeletally mature, he was noted as such as an SA is not assigned. Results The magnitude of intra-individual differences between repeated SA assessments were d = 0.008 year (observer A) and d = 0.001 year (observer B); the respective coefficients of variation were 1.11% and 1.75%. Inter-observer mean differences were negligible (t = 1.252, p = 0.210) and the intra-class correlation coefficient was nearly perfect (ICC = 0.995). Concordance of classifications of players by maturity status between observers was 90%. Conclusion Fels SA assessments were highly reproducible and showed an acceptable level of inter-observer agreement between trained examiners. Classifications of players by skeletal maturity status based on assessments of the two observers were highly concordant, though not 100%. The results highlight the importance of experienced observers in skeletal maturity assessments.

El tenis es un deporte que depende del rendimiento neuromuscular para tener un mejor desempeño, independientemente del nivel de práctica. El objetivo de este estudio fue describir la asociación entre variables antropométricas y rendimiento neuromuscular niños tenistas (n=36) pre-púberes, en un rango de edad de (10.15-12.77) años, además de compararlos según el nivel de práctica. Los participantes fueron divididos en dos grupos, el primero fue denominado “competitivos”, con ranking nacional (n=18) edad (11.66 ± .72) y el segundo denominado “recreativos” sin ranking nacional (n=18) edad (11.52 ± .82). Se realizó una antropometría básica incluyendo estatura, peso y masa grasa, además se ejecutaron pruebas de CMJ, lanzamientos de balón medicinal de 2kg con tres técnicas diferentes (derecha, revés y por encima de la cabeza), y velocidades de 10m y 20m. En la comparación de grupos se encontraron diferencias (p≤0.01) en la masa grasa, CMJ y la prueba de 20m, y (p≤0.05) en los lanzamientos de balón medicinal y 10m. La estatura y el CMJ se asociaron a las otras variables evaluadas y los jugadores de nivel competitivo tuvieron mejores atributos antropométricos y neuromusculares que sus contemporáneos de nivel recreativo, tal vez por adaptaciones en edades pre-púberas al tiempo dedicado a la práctica, y a la exigencia competitiva. Palabras clave: Tenis, deporte infanto-juvenil, potencia, velocidad. Abstract. Tennis is a sport that depends on neuromuscular performance during the game, regardless of the level of practice. This study aimed to describe the association between anthropometric and neuromuscular performance in pre-pubertal children tennis players (n=36) aged (10.15-12.77) years and compare them according to the level of practice. The participants were divided into two groups; the first was called "competitive," with a national ranking (n=18) aged (11.66 ± .72), and the second called "recreational" non-ranked in the national system (n=18) aged (11.52 ± .82). Basic anthropometry, including height, weight, and fat mass, was performed, as well as CMJ tests, 2kg medicine ball throws with three different techniques (forehand, backhand, and overhead), and 10m and 20m distance speeds. The comparison by groups t- student test found differences of (p≤0.01) in fat mass, CMJ, and the 20m test, and (p≤0.05) in the medicine ball throw and 10m. The height and CMJ variables were strongly associated with the other variables evaluated and competitive-level players had fitter anthropometric and neuromuscular attributes than their recreational-level contemporaries, perhaps due to adaptations in pre-pubertal ages to the time dedicated to the practice and the competitive demand. Keywords: Tennis, youth sports, power, speed.

Learning effect occurs when the best performance is not achieved at the earliest trial of a repeated protocol of evaluation. The present study examined, within testing session, the intra-individual variation in an isokinetic strength protocol composed of five reciprocal concentric and eccentric contractions of knee extensors (KE) and knee flexors (KF) among male adolescent swimmers. Additionally, test-retest reliability was determined as intra-individual mean differences between two consecutive testing sessions. The sample included 38 swimmers aged 10.1–13.3 years. A subsample (n = 17) completed a second visit. Isokinetic dynamometry was used to assess concentric and eccentric contractions of KE and KF at an angular velocity of 60°.s-1. The protocol included three preliminary repetitions that were not retained for analysis, a 60-second interval, and five reciprocal maximal concentric contractions (cc). The preceding sequence was repeated for eccentric contractions (ecc) of KE and KF. Multilevel regression confirmed intra-individual and inter-individual levels as significant sources of variance in peak torque (PT) values. Intra-class correlation (ICC) fluctuated between 0.582 and 0.834 and, in general, a substantial percentage of participants need more than three repetitions to attain their best PT: KEcc (36.8%), KEecc (23.7%), KFcc (39.5%), KFecc (18.4%). For the subsample of 17 swimmers who completed a second testing session, intra-individual mean differences of the best PT were trivial or small. In summary, the validity of shorter protocols may be compromised if swimmers do not attain their best peak torque in the first few attempts, and the reliability of a 5-repetition protocol seemed acceptable.

El objetivo de este estudio fue comparar la aptitud física entre jóvenes futbolistas colombianos y describirlas según el pico de velocidad de crecimiento. Participaron 58 jugadores de edades comprendidas entre 13,46 y 15,31 años. Se evaluó una antropometría básica y se determinó el pico de velocidad de crecimiento PVC, también se aplicaron seis pruebas físicas relacionadas con fuerza, velocidad y agilidad. Se realizaron gráficas de dispersión de las pruebas físicas según el PVC, múltiples correlaciones entre variables y, finalmente, la población se dividió en tres grupos según el club al que pertenecen los jugadores haciendo una comparación ANOVA entre club A, club B y club C. Aparentemente, el PVC describe las pruebas de fuerza-potencia en mayor medida que las pruebas de agilidad según la apreciación de las gráficas de dispersión. En las múltiples correlaciones se evidencia una gran asociación entre el CMJ con las otras pruebas; en la comparación de clubes, el club A tuvo jugadores más altos, más pesados y con un PVC más adelantado, así mismo presentó mejor rendimiento en las pruebas, principalmente en CMJ F=13,813 P<0,01, Lanzamiento Balón Medicinal F = 11,053 P<0,01, Velocidad de Remate F = 18,916 P<0,01, y Repeated Sprint Ability F=12,950 P<0,01. Se concluye que la influencia de las condiciones antropométricas favorables se relaciona con un mejor desempeño en las pruebas físicas en esta población de jóvenes futbolistas que se encuentran en la época del salto de crecimiento.