Somatotype, Accumulated Workload, and Fitness Parameters in Elite Youth Players: Associations with Playing Position.

The purpose of this study was three-fold: (1) to describe anthropometric, maturation, and somatotype differences of players based on playing positions; (2) to analyze variations of accumulated load training (AcL) and fitness parameters between playing positions; and finally (3) to explain the variation of maximal oxygen uptake (VO2max) and peak power (PP) through the AcL, body fat (BF), maturity, somatotype and fitness levels. Twenty-seven male youth soccer players under-16 were divided by the following positions participated in this study: six central midfielders, four wingers (WG), five forwards, eight defenders, and four goalkeepers (GK). They were evaluated on two occasions: pre-season and after-season. Height, sitting height, body mass, BF, girths, percentage of BF (BF%), lean body mass, maturity, somatotype, sprint test, change of direction test, Yo-Yo intermittent recovery test level 1, Wingate, PP, VO2max and fatigue index were assessed. Then, AcL was monitored during training sessions. The main results revealed significant differences between player positions for maturity offset (p = 0.001), for BF (p = 0.006), BF% (p = 0.015), and lean body mass kg (p = 0.003). Also, there were significant differences for AcL and fatigue index in pre-season between player positions (p < 0.05). In addition, there were some significant differences in pre- and after-season for VO2max and PP between player positions (p < 0.05). In conclusion, GK showed higher values in anthropometric, body composition variables and maturity offset compared to the other positions, while WG presented lower levels of BF. In pre-season, there were more differences by player positions for the different variables analyzed than after-season that reinforces the tactical role of the positions, and the emphasis in increased load in the beginning of the season. This study could be used by coaches, staff, and researchers as a reference for athletes of the same sex, age, and competitive level.

Fluctuations in Well-Being Based on Position in Elite Young Soccer Players during a Full Season.

The current study surveyed weekly and daily variations of well-being ratings relative to the Hooper Index (HI): fatigue (wFatigue), stress (wStress), delayed onset muscle soreness (wDOMS), and sleep quality (wSleep) during a soccer season based on players' positions. The full-season was divided into three meso-cycles: Early season, week (W)1 to W7; Mid-season, W8 to W13, and End-season, W14 to W20. Twenty-six young players participated in the study (age, 15.5 ± 0.2 years; height, 172.9 ± 4.2 cm; body mass, 61.4 ± 5.6 kg; body fat, 8.6 ± 2.9%; VO2max, 48.4 ± 2.4 mL.kg-1·min-1; maturity offset, 1.9 ± 0.3 years). Participants played in the same team and competed in Iran national under-16 competitions. Well-being status was monitored on training days using the HI questionnaire. The main result was a significant difference between well-being status 5 days before match day (MD) and 4 days before MD, compared to MD for all playing positions (p ≤ 0.001). The highest and lowest records occurred during End-season for wDOMS (strikers = 11.5 ± 8.4 arbitrary units (AU)), Early season (central defenders = 9.5 ± 0.7 AU) and for wFatigue (central midfielders = 11.4 ± 0.9 AU), and Early season (wide defenders = 9.7 ± 0.7 AU), respectively. Overall, the results showed a significant increase in wStress and wSleep for all players' positions from Early- to End-season. The main application of this study is to make coaches aware of their players' well-being fluctuations throughout the full season, especially in young elite soccer players, and to avoid injuries, overtraining, and overreaching as much as possible.

Obesidad, intervención escolar, actividad física y estilos de vida saludable en niños españoles / Obesity, School Intervention; Physical Activity and Healthy Lifestyles in Spanish Children

Introducción: El sobrepeso y la obesidad en la infancia y la adolescencia se han incrementado a nivel mundial durante las últimas décadas. Este hecho se asocia, principalmente, con la falta de actividad física, hábitos de vida y comportamientos alimenticios poco saludables. Objetivo: Analizar la efectividad de diferentes estudios de intervención escolar llevados a cabo en España para prevenir y tratar la obesidad en niños y niñas. Métodos: Se realizó una estrategia de búsqueda electrónica utilizando las bases de datos PubMed, Medline y SPORTdiscus y los términos school-based intervention, Spain, healthy lifestyle, obesity prevention, physical activity y nutrition childhood obesity y children obesity. Se identificaron 124 artículos y solo 11 cumplieron los criterios de inclusión. Conclusiones: Las intervenciones realizadas por el entorno escolar no fueron eficaces o significativas para cambiar los indicadores antropométricos de los niños, niñas y adolescentes españoles. Sin embargo, las intervenciones escolares unidas a la implicación familiar, pueden ser eficaces para modificar cambios en los hábitos nutricionales, nivel de actividad física y hábitos de vida saludable en la etapa infantojuvenil, ya que son los principales determinantes de obesidad en la infancia. Por último, la consolidación de un adecuado estilo de vida en etapas tempranas puede prevenir la obesidad y sobrepeso en la adultez(AU)

Introduction: Overweight and obesity in childhood and adolescence have increased worldwide in recent decades. This fact is associated mainly with a lack of physical activity, unhealthy lifestyle habits and eating behaviors. Objective: To analyze the effectiveness of different school intervention studies carried out in Spain to prevent and treat obesity in boys and girls. Methods: An electronic search strategy was carried out using the PubMed, Medline and SPORTdiscus databases, under the terms school-based intervention, Spain, healthy lifestyle, obesity prevention, physical activity, nutrition, childhood obesity and children obesity. 124 articles were identified and only 11 met the inclusion criteria. Conclusions: The interventions carried out by school were not effective or significant to change the anthropometric indicators of Spanish children and adolescents. However, school interventions, together with family involvement, can be effective in modifying changes in nutritional habits, level of physical activity and healthy lifestyle habits in the infant-juvenile stage, since they are the main determinants of obesity in childhood. Finally, establishing an adequate lifestyle early can prevent obesity and overweight in adulthood(AU)

Associations between Inter-Limb Asymmetries in Jump and Change of Direction Speed Tests and Physical Performance in Adolescent Female Soccer Players.

The association between asymmetries in jump and change of direction (COD) with physical performance in several sports show inconclusive results. The purposes of this study were to: (1) measure inter-limb asymmetries in three distinct groups in adolescent female soccer players and, (2) to determine the association between inter-limb asymmetries and physical performance in different age groups. Fifty-four players were distributed in three age groups: U-18, U-16 and U-14. All of them performed a series of jumps, sprints and change of direction speed tests. Asymmetries were assessed as the percentage difference between limbs, with the equation: 100/Max value (right and left) * in value (right and left) * -1 + 100. Mean inter-limb asymmetries were 2.91%, 4.82% and 11.6% for 180° COD, single leg hop and single leg countermovement jump tests respectively, but higher percentages of asymmetries were observed in many players individually. U-18 and U-16 showed significant differences on 180° left COD compared to U-14. Effect size (ES): 0.80 and 0.74, respectively; U-18 presented differences on single left leg hop test compared to U-14, ES: -0.72; U-16 also showed differences on 40 m speed compared to U-14, ES 0.87 (All p < 0.05). Jumping and COD physical tests show asymmetries in adolescent female soccer players, but these asymmetries do not interfere with physical performance. The largest asymmetry was observed in the single leg countermovement jump, and no asymmetries between groups were found. Due to the high variability in the direction of asymmetries, it is recommended to consider players' individual asymmetries for designing specific training programs.

Effects of Strength vs. Plyometric Training Programs on Vertical Jumping, Linear Sprint and Change of Direction Speed Performance in Female Soccer Players: A Systematic Review and Meta-Analysis.

The main purpose of this systematic review and meta-analysis was to compare the effects of strength training (ST) and plyometric training (PT) on vertical jump, linear sprint and change of direction (COD) performance in female soccer players. A systematic search of the PubMed, Web of Science, Google Scholar and SportDiscus databases revealed 12 studies satisfying the inclusion criteria. The inverse-variance random-effects model for meta-analyses was used. Effect sizes (ES) were represented by the standardized mean difference and presented alongside 95% confidence intervals (CI). The magnitude of the main effect was small to moderate (vertical jump (ES 0.53 (95% CI-0.11, 0.95), Z = 2.47 (p = 0.01); linear sprint (ES -0.66 (95% CI-2.03, -0.21), Z = 2.20 (p = 0.03); COD (ES -0.36 (95% CI-0.68, -0.03), Z = 2.17 (p = 0.03)). Subgroup analyses were performed (i.e., ST and PT duration, frequency, session duration and total number of sessions), revealing no significant subgroup differences (p = 0.12-0.88). In conclusion, PT provides better benefits than ST to improve vertical jump, linear sprint and COD performance in female soccer players. However, significant limitations in the current literature prevent assured PT and ST prescription recommendations being made.

Effects of Combined Strength and Power Training on Physical Performance and Interlimb Asymmetries in Adolescent Female Soccer Players.

PURPOSE: To examine the effects of an 8-week combined strength and power training intervention on physical performance and interlimb asymmetries in adolescent female soccer players. METHODS: Thirty-seven adolescent female soccer players (age 16.1 [1.1] y) were randomly assigned to a control group (n = 18) or experimental group (n = 19). The experimental group performed combined strength and power training twice a week, which consisted of strength and power exercises that trained the major muscles of the lower body and trunk musculature. Preintervention and postintervention tests included unilateral and bilateral horizontal and countermovement jump tests, a 40-m sprint test (10- and 30-m split times), a 10-m sprint with a 180° change-of-direction (COD) test, and a multiple-COD test (V-cut test). Asymmetries were also analyzed in the unilateral tests. RESULTS: Significant group-by-time interaction of the improvement between pretest and posttest was observed for speed (effect size [ES]: -1.30 to -1.16) and COD tests (ES: -0.62 to -0.61) but not in jumping (ES: -0.09 to 0.28) and interlimb-asymmetry tests (ES: -0.13 to 0.57). CONCLUSIONS: The short-term in-season combined strength and power training program induced greater speed and COD performance improvements than soccer training alone in adolescent female soccer players.

Basal and post-exercise heart rate variability correlates with training load in endurance athletes / La variabilidad de la frecuencia cardíaca basal y posterior al ejercicio correlaciona con la carga de entrenamiento en atletas de resistencia / A variabilidade da frequência cardíaca basai e pós-exercício está correlacionada com a carga de treinamento em atletas de resistência

OBJECTIVE: Heart rate variability has been proposed as a valid method to examine the individual response to training load in endurance athletes. Thanks to this tool, the relationship between basal and post-exercise Heart rate variability measurements can be analyzed during a microcycle (one week) using straight values or their coefficients of variation. METHOD: Ten amateur endurance athletes (n = 5 men, n = 5 women) were monitored during a 7-day microcycle that included three road-cycling sessions, two running sessions and two trail-running sessions. The RR series were measured for 5 minutes upon wake up and after training, in a seating position, using a chest strap. RESULTS: Basal and post-exercise Heart rate variability measurements showed high correlation when weekly mean values were used, very similar to when coefficients of variation values were used. In women, the root mean square of successive differences (RMSSD) was: r= 0.73; RMSSD coefficients of variation (RMSSDcv) was: r= 0.66; natural logarithm (Ln) RMSSD: r= 0.68; LnRMSSDcv: r= 0.79; and in men it RMSSD was: r= 0.78; RMSSDcv: r= -0.62; LnRMSSD: r= 0.75; LnRMSSDcv: r= -0.73). CONCLUSION: the relationship between these two measurements could be useful to program the training loads of the following microcycle

OBJETIVO: La variabilidad de la frecuencia cardíaca se ha propuesto como un método válido para examinar la respuesta individual a la carga de entrenamiento en atletas de resistencia. El objetivo de este estudio fue analizar la relación entre las mediciones basales y post ejercicio durante un microciclo (una semana) utilizando valores directos o sus coeficientes de variación. MÉTODO: Se monitorizó a diez atletas aficionados de resistencia durante un microciclo de 7 días, que incluyó tres sesiones de ciclismo de ruta, dos sesiones de carrera y dos sesiones de trail running. Las series RR se midieron durante 5 minutos al despertar y después del entrenamiento, en posición sentado, utilizando una banda torácica. RESULTADOS: Las mediciones de variabilidad de la frecuencia cardíaca basales y post ejercicio mostraron una alta correlación cuando se usaron valores medios semanales, como cuando se usaron valores de los coeficientes de variación. En mujeres, la raíz cuadrada de la media de las diferencias de la suma de los cuadrados entre intervalos RR adyacentes (RMSSD) fue: r = 0.73; el coeficiente de variación (cv) de la RMSSD fue RMSSDcv: r = 0.66; el logaritmo natural (Ln) de la RMSSD (LnRMSSD) fue: r = 0.68; LnRMSSDcv: r = 0.79; y en los hombres fueron RMSSD: r = 0.78; RMSSDcv: r = -0.62; LnRMSSD: r = 0.75; LnRMSSDcv: r = -0.73. CONCLUSIONES: La relación entre estas dos mediciones podría ser útil para el programa de entrenamiento del microciclo posterior

OBJETIVO: A variação da frequência cardíaca tem sido utilizada como método de análise de respostas individuais a carga de treino em atletas de endurance. Graças a esta ferramenta, a relação entre a variação da frequência cardíaca basal e pós-exercício pode ser analisada durante um microciclo (uma semana) usando valores diretos ou seus coeficientes de variação. MÉTODO: Dez atletas de endurance amadores (n = 5 homens, n = 5 mulheres) foram monitorados durante microciclos de 7 dias que incluíram 3 sessões de ciclismo em estrada, duas sessões de corrida e duas sessões de corrida em trilha. As series de RR foram medidas durante 5 minutos depois de acordar e depois do exercício, em posição sentada, com recurso a cardiofrenquencímetros toráxicos. RESULTADOS: Os resultados mostram uma correlação alta entre as medidas de variação de frequência cardíaca basal e pós-exercício quando utilizados valores médios semanais, muito semelhantes aos resultados quando utilizados coeficientes de variação. Nas mulheres, a raiz quadrada media das diferenças sucessivas (RMSSD) foi: r= 0.73; coeficientes de variação RMSSD, (RMSSDcv) foi: r= 0.66; logaritmo natural (Ln) RMSSD: r = 0.68; LnRMSSDcv: r= 0.79; e nos homens, raiz quadrada media das diferenças sucessivas r= 0.78; RMSSDcv: r= -0.62; LnRMSSD: r= 0.75; LnRMSSDcv: r= -0.73). CONCLUSÃO: a relação entre estas duas medidas poderia ser útil para prescrição de cargas de treino dos microciclos seguintes

Determining the reliability and usability of change of direction speed tests in adolescent female soccer players: a systematic review.

INTRODUCTION: This review aimed 1) to describe the most common tests used for assessing change of direction (COD) performance; 2) to detail the reliability of current COD tests; 3) to provide an overview of current intervention strategies used to improve COD performance in adolescent female soccer players. EVIDENCE ACQUISITION: A computerized search was conducted in the PubMed, Cochrane Plus and Web of Science (from 1995 to January 2020) for English and Spanish language and peer-reviewed investigations. EVIDENCE SYNTHESIS: A total of 221 studies were identified, with only 16 meeting the specific search criteria. The main findings were that eleven different tests have been used to assess COD performance with intraclass correlation coefficient and coefficient of variation values between 0.72-0.99 and 1-10.6%, respectively. The number of CODs performed during each test ranged from 1 to 9 within a range of 45º to 180º and with a duration <5 s, 5-9 s and >10 s. CONCLUSIONS: Findings indicate that the reliability of the COD tests seems to depend on: the equipment used, the surface tested on and the technical level of the soccer player. These results should be interpreted with caution as they may be influenced by the period of growth and maturation, the playing position of the player and the period of the soccer season. Finally, strength and power drills could be considered as appropriate to improve COD performance.

Adolescent female soccer players' soccer-specific warm-up effects on performance and inter-limb asymmetries.

No studies have assessed whether changes in physical performance and inter-limb asymmetries (ILA) can be achieved with the FIFA 11+ prevention programme in adolescent female soccer players. The aim of this study was to assess the effect of the FIFA 11+ programme compared with a standard warm-up on physical performance and ILA in adolescent female soccer players. Thirty-six adolescent female soccer players were randomly assigned to an experimental (EG; n = 19) or a control group (CG; n = 17). Unilateral/bilateral countermovement jump (CMJ), drop jump (DJ) and horizontal jump tests, two different change of direction tests, an ankle dorsiflexion test, the Y-Balance test (YBT) and inter-limb asymmetries were measured before and after 10 weeks of training. The results revealed no significant group-by-time interactions in the vast majority of variables (p>0.05). Paired t-test revealed significant improvements of the right [effect size (ES):0.56] and left (ES:0.49) CMJ, right (ES:0.74) and left (ES:0.54) DJ (ES:0.74), right (ES:1.27) and left (ES:1.26) posteromedial direction and right (ES:0.89) and left (ES:0.84) posterolateral direction in the YBT in the EG (p < 0.05). Right anterior direction in the YBT and V-cut test were significantly improved in both groups (p<0.05). For inter-limb asymmetry variables, no significant group-by-time interactions (ES:0 to 0.93) and an improvement between pre- and post-tests (ES:-0.76 to 0.49) were observed. Therefore, the FIFA 11+ programme led to improved unilateral jumping, dynamic balance and reduced lower extremity symmetries of several tests in adolescent female soccer players.

Efectos hormonales y hematológicos en una marcha invernal de baja altitud en militares chilenos / Hormonal and hematological effects in a low-altitude winter march in chilean military

Introducción: Las exposiciones intermitentes a gran altitud tienen efectos agudos sobre algunos marcadores biológicos, como la testosterona, pero no así en baja altitud. Dado que el entrenamiento de soldados debería ir asociado a tareas militares específicas, adquiere gran importancia valorar los cambios fisiológicos que puedan producirse en determinadas circunstancias (como la altitud) pero durante la realización de actividades propias de las unidades militares. Objetivo: Identificar los cambios hematológicos y en las hormonas Testosterona Libre (TL), Testosterona Total (TT ) y Cortisol en una marcha nocturna a baja altitud en soldados de operaciones en montaña. Metodología: 32 Militares masculinos (26,3 ± 4,50 años, 75,1 ± 7,6 kg) realizaron una marcha invernal nocturna con equipo y un desnivel entre los 902 y 1648 m. Se obtuvieron muestras de sangre antes y después de la marcha y se midió TL, TT, cortisol y hemograma: hematíes (Hmt), hemoglobina (Hb), hematocrito (Htto) y volumen corpuscular medio (VCM). Resultados: Se produjo un descenso significativo de los valores de TL y TT sin cambios en el cortisol plasmático. También se observó un descenso en las cifras de Hmt, Hb, Htto y VCM. Conclusión: Una marcha invernal con equipo de combate, en baja altitud y con un desnivel de 746 m, produce un descenso significativo de los valores plasmáticos de Testosterona (libre y total) en soldados de una unidad de operaciones en montaña. No se observan cambios en los valores de cortisol. Se detecta una reducción significativa de hematíes, hemoglobina, hematocrito y VCM que podrían deberse a un efecto de hemodilución

Introduction: Intermittent exposures at high altitude have acute effects on some biological markers, such as testosterone, but not at low altitude. Since the training of soldiers should carry out specific military activities, is very important to asses physiological changes that can occur in particular circumstances (such as altitude) but during the performance of the activities of the military units. Objective: To identify the hematological changes and the hormones Free Testosterone (TL), Total Testosterone (TT ) and Cortisol during a nocturnal march at low altitude in soldiers of mountain operations. Methodology: 32 male military (26.3 ± 4.50 years, 75.1 ± 7.6 kg) performed a nocturnal winter march with equipment between 902 and 1648 m of altitude. Blood samples were obtained before and after the march, and TL, TT, cortisol and blood count were measured: red blood cells (Hmt), hemoglobin (Hb), hematocrit (Htto) and mean corpuscular volume (MCV ). Results: There was a significant decrease in TL and TT values without changes in plasmatic cortisol. A reduction in the values of Hmt, Hb, Htto and VCM has also been observed. Conclusion: A winter march with combat equipment, at low altitude and with a unevenness of 746 m, produces a significant decrease in the plasma values of Testosterone (free and total) in soldiers of mountain operations. No changes in cortisol values are observed. A significant reduction of red blood cells, hemoglobin, hematocrit and MCV is detected, which could be due to a hemodilution effect

Efectos de las plataformas vibratorias en la salud ósea en mujeres posmenopáusicas / Effects of Vibratory Platforms on Bone Health in Postmenopausal Women

Estudios recientes han sugerido que los estímulos mecánicos (vibraciones) de alta frecuencia y baja magnitud pueden ejercer un efecto positivo sobre la morfología ósea y beneficiar su cantidad y calidad. La plataforma vibratoria es una máquina popular que se introdujo en la última década como una nueva promesa contra el tratamiento de la osteoporosis. Actualmente, en el mundo hay más de 200 millones de mujeres posmenopáusicas que sufren osteoporosis. Esta enfermedad es una de las más comunes y costosas de la salud pública. El ejercicio físico complementado con el tratamiento vibratorio puede que sea considerado como una estrategia efectiva para la prevención y tratamiento de la osteoporosis posmenopáusica. Esta revisión ofrece una visión general de cuestiones significativas relacionadas con la terapia con la plataforma vibratoria para la prevención y tratamiento de la osteoporosis en mujeres postmenopáusicas. El objetivo de esta revisión ha sido conocer los últimos avances de entrenamiento con plataformas vibratorias para la mejoría de la masa ósea en mujeres posmenopáusicas. Existe una gran discrepancia respecto al uso de estas como tratamiento osteoporósico, uso de diferentes tipos de plataformas, distintas frecuencias, amplitud, aceleración o duración del tratamiento. La escasa literatura estableció que la plataforma vibratoria Galileo es la que más se utiliza en dicha población, pero se necesitan más intervenciones para concretar los beneficios y daños de este tratamiento en mujeres postmenopáusicas(AU)

Recent studies have suggested that mechanical stimuli (vibrations) of high frequency and low magnitude can exert a positive effect on bone morphology and benefit quantity and quality. The vibrating platform is a popular machine introduced in the last decade as a new promise against the treatment of osteoporosis. Currently, there are more than 200 million postmenopausal women in the world suffering from osteoporosis. This disease is one of the most common and expensive in public health. Physical exercise supplemented with vibrational treatment may be considered an effective strategy for the prevention and treatment of postmenopausal osteoporosis. This review offers an overview of significant issues related to therapy with the vibration platform for the prevention and treatment of osteoporosis in postmenopausal women. The objective of this review is to know the latest advances in vibratory platforms training for the improvement of bone mass in postmenopausal women. There is a great discrepancy regarding the use of vibratory platforms as osteoporosis treatment, the use of different types of platforms, different frequencies, amplitude, acceleration or duration of treatment. The limited literature established that Galileo vibration platform is the most used in this population, but more interventions are needed to grasp the benefits and harms of this treatment in postmenopausal women(AU)

Programas de entrenamiento para mejorar el rendimiento en jóvenes tenistas: revisión sistemática / Training programs to improve performance in young tennis players: systematic review

En los últimos años, el tenis ha crecido en popularidad, provocando que la competitividad se haya incrementado considerablemente en todos los grupos de edad. Los jugadores de tenis, para ser competitivos y alcanzar el éxito, requieren de un alto nivel de desarrollo en cuatro habilidades fundamentales: táctica, técnica, física y psicológica. A la hora de diseñar programas de entrenamiento para los tenistas, es importante tener en cuenta los requerimiento físicos y fisiológicos de los jugadores, ya que pueden variar según el nivel del jugador, el estilo de juego, el sexo o la superficie de la pista, entre otros. Estas habilidades fundamentales y requerimientos se deben trabajar en edades tempranas para lograr el éxito en edades adultas, por lo tanto, el objetivo de la presente revisión sistemática fue estudiar las características de los programas de entrenamiento que se han llevado a cabo en jóvenes tenistas para mejorar su rendimiento. Se realizó una estrategia de búsqueda electrónica utilizando las bases de datos PubMed, SPORTDiscus y los términos tennis, performance, adolescent, male, female, training e intervention. Veintitrés artículos fueron revisados y solo 7 cumplieron los criterios de inclusión. El programa de entrenamiento pliométrico es el más utilizado para mejorar el rendimiento de los jóvenes tenistas, siendo un programa de corta duración, barato y de fácil cumplimentación para entrenadores y preparadores físicos de tenis. Esta revisión sistemática podría contribuir al diseño de futuros programas de entrenamiento para mejorar el rendimiento de jóvenes tenistas(AU)

In recent years, tennis has grown in popularity, causing competitiveness to have increased significantly in all age groups. Tennis players, in order to be competitive and achieve success, require a high level of development in four fundamental skills: tactical, technical, physical and psychological. When designing training programs for tennis players, it is important to take into account the physical and physiological requirements of the players, as they may vary according to player level, the play style, sex or track surface, among others. These fundamental skills and requirements must be worked at an early age to achieve success in adult ages, therefore, the systematic review objective was to study the training programs characteristics in young tennis players for improve their performance. An electronic search strategy was performed using PubMed, SPORTDiscus and the terms tennis, performance, adolescent, male, female, training and intervention. Twenty-three articles were reviewed and only seven met the inclusion criteria. The plyometric training program is the most used to performance improve of young tennis players, being a short, inexpensive and easy rogram for tennis trainers. This systematic review could contribute to future design for training programs to performance improve of young tennis players(AU)

Factors affecting children and adolescents 50 meter performance in freestyle swimming.

BACKGROUND: This study investigated which factors influence performance in a short distance swimming test (50-meters) in adolescent swimmers. METHODS: Freestyle 50-meter personal best time (PBT) was registered for 67 swimmers (14.3±2.2 y; 46 males). Handgrip (HG), standing broad jump (SBJ), isometric knee-extension (KE), time to run 30 meters (V30m), maximal estimated oxygen-consumption (VO2max), swimming-technique (CTE), height, weight, fat mass, body fat percentage (BF%) and fat-free mass (FFM) were measured. Variables that presented correlation with PBT were further examined using multiple linear regressions. RESULTS: PBT was correlated with SBJ, VO2max, HG, KE, CTE, Weight, Height, FFM, BF% and swimming hours per week (SHW). Multiple linear regressions showed that PBT was associated to Height, V30m, CTE and SBJ. Sex and age did not modify these associations. CONCLUSIONS: PBT was found to be mainly associated with height, an anthropometric variable. SBJ and V30m, both fitness-related variables, highly influenced by muscle fiber type were also predictors, suggesting that for short distances physiological factors might be determinant to performance. Age modified predictive values suggesting that this is also a key factor to performance, and thus competitions during adolescence should be organized according to year of birth rather than by age category.