Longitudinal study of repeated sprint performance in youth soccer players of contrasting skeletal maturity status.

The purpose of the study was to evaluate the developmental changes in performance in a repeated-sprint ability (RSA) test in young soccer players of contrasting maturity status. A total of 83 regional level Portuguese youth soccer players, aged 11-13 years at baseline was assessed annually. Stature, body mass, 7x34.2-m sprint protocol (25-s active recovery), 20-m multi-stage continuous shuttle endurance run and counter-movement jump (CMJ) without the use of the arms were measured. Fat-free mass (FFM) was determined by age and gender-specific formulas. Developmental changes in total sprint time across ages were predicted using multilevel modeling. Corresponding measurements were performed on an independent cross-sectional subsample of 52 youth soccer players 11-17 years to evaluate the predictive model. CA, CA(2), maturational status (SA-CA), body size (mass and stature), FFM, aerobic endurance, lower limb explosive strength and annual volume training significantly improved the statistical fit of the RSA multilevel model. In 'late' maturing athletes, the best model for predicting change in RSA was expressed by the following equation: 86.54 - 2.87 x CA + 0.05 x CA(2) - 0.25 x FFM + 0.15 x body mass + 0.05 x stature - 0.05 x aerobic endurance - 0.09 x lower limb explosive strength - 0.01 x annual volume training. The best fitting models for players who were 'on time' and 'early' maturing were identical to the best model for late maturing players, less 0.64 seconds and 1.74 seconds, respectively. Multilevel modeling provided performance curves that permitted the prediction of individual RSA performance across adolescent years in regional level soccer players. Key pointsRepeated-sprint ability tests are a valuable sport-specific field test of sprint performance in youth soccer players. Here, the test had reasonable reliability and can be useful to trainers and coaches in the assessment of young athletes and in monitoring changes over time.The total sprint time of youth soccer players advanced in biological maturation improves more, on average, than that of players who are on time (average) and late in maturation. The performance difference between early and late maturing players is consistent after about 13 years of age.Multilevel modeling is a promising statistical technique for analyzing the development of functional capacity in a sport. It has the potential to provide useful information to assist trainers and coaches in evaluating and facilitating the development of individual players.

Prevalence of overweight, obesity and physical activity levels in children from Azores Islands.

BACKGROUND: Childhood overweight and obesity are increasing all over the world and have been associated with low levels of physical activity (PA). AIMS: To determine the prevalence of overweight, obesity and PA levels in Azorean children according to age and sex; and to determine the association between levels of PA and prevalence of overweight and obesity. SUBJECTS AND METHODS: Weight, height and PA levels were measured in 3699 children aged 6-10 years, from the Azores Islands, Portugal. Overweight and obesity were classified according to the cut-offs of Cole et al. (BMJ 320:1240-1243, 2000) . RESULTS: In girls, prevalences of overweight and obesity were 22.8% and 13.2%, and in boys 17.6% and 12.3%, respectively. No age trends were found in the prevalence of overweight or obesity; however, girls had a higher risk of being overweight (OR = 1.4, 95% CI = 1.2-1.7) than boys. Levels of PA were higher in boys compared to girls (F(1) = 52.8, p < 0.001). A protective effect of PA practice (very active versus less active) was observed for obesity (OR = 0.7; 95% CI = 0.5-0.9). CONCLUSION: The results demonstrate the existence of high prevalence of overweight and obesity in children from the Azores Islands, which is associated with low levels of PA.

Top 50 most-cited articles in medicine and science in football.

OBJECTIVES: To conduct a comprehensive mapping analysis to the scientific literature published in football aiming to identify the areas of bigger interest and potential for further exploration. METHODS: The data were obtained by a search conducted on the Web of Science. Articles were listed based on citation frequency. We used an open-source bibliometrix R-package for the comprehensive bibliometric analyses. RESULTS: The number of citations per article ranged from 251 to 869 (median 323; IQR 125). The yearly number of citations ranged from 8 to 54 (median 26; IQR 11). Most of the articles (76%) were of level III of evidence, 10% were level II and 14% were level IV. Within the top 50 most-cited articles, 40 articles were original research (37 observational and 3 experimental studies), 9 were review articles and 1 was a thesis. From the 40 original research articles, 50% involved elite players, 73% were exclusive to male players and 80% involved adult players only. The topic area with the highest number of articles was sports medicine (44%), followed by training and testing (32%), performance analysis (14%) and physiology (10%). No study within the top 50 was devoted to biomechanics, nutrition, sport psychology, coaching or social sciences. CONCLUSIONS: The lack of experimental studies within the top 50 most-cited articles in football clearly underpins how far we still are from establishing the theoretical and methodological guidelines for the applied science and medicine in football.