The purpose of this study was to evaluate whether Branched-chain amino acids (BCAAs) supplementation had any beneficial effects on growth and metabolic parameters of young rats submitted to chronic aerobic exercise. Thirty-two young rats (age: 21-d) were randomly assigned to four experimental groups (n = 8): Supplemented Trained (Sup/Ex), Control Trained (Ctrl/Ex), Supplemented Sedentary (Sup/Sed) and Control Sedentary (Ctrl/Sed). The trained groups underwent a five-week swimming protocol and received supplemented (45 mg BCAA/body weight/day) or control ration. Trained animals presented a lower body length and a higher cartilage weight, regardless of supplementation. Physical activity was responsible for a substantial reduction in proteoglycan synthesis in cartilage tissue, and BCAA supplementation was able to attenuate this reduction and also to improve glycogen stores in the liver, although no major differences were found in body growth associated to this supplementation.

• Cartilage proteoglycan synthesis was dramatically reduced in trained animals as a whole.

• BCAA supplementation augmented liver glycogen stores and reduced proteolysis in our experimental conditions

• Trained animals receiving BCAA supplementation featured increased proteoglycan synthesis compared to sedentary ones, probably because BCAA may have attenuated the negative effects of exercise on cartilage development.

• BCAA supplementation was not capable of neutralizing directly the negative effects of long-term physical training and lower food intake in young male rats on body growth