This is a correlational field study which sought to determine the relationship between the biological maturation and muscle power of the upper members of youth swimmers. Twenty-three children aged 10 to 13 were evaluated. The sample was described using anthropometric measurements: height, body mass, arm span, body composition, body surface area and sexual \u00admaturation (Tanner, 1975). We applied the Wingate test (laboratory and pool) for upper members, according to Dotan and Bar-Or (1983) and Morouco (2009), to estimate maximum power, relative power, average power and the fatigue index. The data are presented in central tendency and dispersion measures; one-factor differences were calculated and correlations were estimated using the Pearson and Spearman technique. The results show that training outside the water influences performance in the water. The body size and the number of hours of training affected the power produced by the swimmers, with notable differences after the age of 10. The body size and greater frequency of weekly training generated high muscle power values. Periodic evaluations of strength and power are recommended, along with creating anthropometric profiles and keeping them updated, applying self-evaluation questionnaires of sexual maturation, and adjusting the length of training as ages increase.<\/p>\n\n