Objective:To analyse the effect of extracurricular physical activities on fat mass accumulation and physical fitness during growth in early pubertal males.Design:Longitudinal study.Subjects:A total of 42 male children (9.4±1.4 years, Tanner I–II and 12.7±1.5 years, Tanner III–IV, before and after the 3.3 years follow-up, respectively), randomly sampled from the population of Gran Canaria (Spain), 26 of them physically active (PA, at least 3 h per week during 3 years) and 16 non-physically active (non-PA).Measurements:Body composition (dual-energy X-ray absorptiometry), anthropometrics (body circumferences and skinfolds) and physical fitness variables (dynamic and isometric force, anaerobic capacity and maximal aerobic power) were determined in all subjects.Results:Both groups had comparable body sizes at the start and the end of the study. Body mass index increased with growth more in the PA than in the non-PA group (P