AIM: More than ever young athletes are training intensively and compete at high levels. As adolescent athletes are training in a period associated with many changes in growth and maturation longitudinal studies are important to elucidate the development in physical parameters. The aim of this study was to evaluate the development in aerobic power in elite as well as non-elite soccer players during the years of puberty and to relate it to maturation as well as hemoglobin and hematocrit. METHODS: Forty-nine young male soccer players at elite and non-elite levels (10.5-13 y) were recruited as subjects. All subjects were tested 4 times over a period of 3.5 years. Anthropometrical parameters including skinfold were measured. VO2max was assessed during treadmill run, testicular volume and testosterone levels were used to estimate maturation, and hemoglobin (Hb) as well as hematocrit (Htc) was measured from blood samples. RESULTS: A longitudinal development in VO2max (l/min) was found for all players together. The elite players have higher values and steeper increase compared to non elite-players. This difference was still present when VO2max was adjusted for body weight (ml/kg/min). CONCLUSIONS: The general development in VO2max was significantly correlated to the development in Hb and Htc as well as maturation, but the difference between elite and non-elite players could not be explained from differences in these variables. As elite players often are selected at a very young age it is possible that training effect is present but it cannot be excluded that genetic factors may play an important role.
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