RESUMEN
OBJECTIVE: To analyze the relationship between resistance training and body composition in adolescents. METHODS: A longitudinal 12-month follow up of 190 adolescents of both sexes categorized into three groups according to resistance training practice, as non-engagement (n=121), irregular engagement (n=44), and frequent engagement (n=25). The outcomes adopted were bone mineral density (BMD), lean soft tissue (LST), and body fatness (BF). RESULTS: Adolescents frequently engaged in resistance training presented higher gains in mean (95 CI) LST [6.1 (3.7 to 8.5) kg vs 2.4 (1.4 to 3.4) kg; P= 0.027] and BMD-upper limbs [0.096 (0.072 to 0.121) g/cm2 vs 0.046 (0.036 to 0.056) g/cm2; P=0.002] than adolescents who were not engaged in resistance training, respectively. Findings were more consistent for boys than girls (models were not significant among girls: LST P= 0.721; BMD-upper limbs P= 0.053). CONCLUSION: Regular engagement in resistance training was related to higher gains in muscle mass and bone density, especially among boys.