Influence of extracurricular sport activities on body composition and physical fitness in boys: a 3-year longitudinal study. - Ara,I.; Vicente-Rodriguez,G.; Perez-Gomez,J.; Jimenez-Ramirez,J.; Serrano-Sanchez,JA.; Dorado,C.; Calbet,JA. (Int J Obes (Lond), 2006)