Amino acids are the building blocks of all body proteins, including structural proteins that build muscle, connective tissues, bones and other structures, while supplying the body with the nitrogen essential for the growth and maintenance of all tissues. Branched-chain amino acids are crucial to an athlete’s recovery and muscle tissue repair following strength competitions such as body building and powerlifting, and other anaerobic and aerobic exercises. Leucine, isoleucine and valine work synergistically together and are responsible for supporting muscle protein synthesis, and promoting strength and muscle enhancement. In the human diet, leucine naturally occurs in greater amounts compared to isoleucine and valine; as such, it is believed that an effective branched-chain amino acid (BCAA) supplement includes a higher ratio of leucine. Human studies show high leucine supplementation including isoleucine and valine result in a greater muscle protein synthesis response during recovery.

Male athletes were supplemented with BCAAs or a low-carbohydrate drink for eight consecutive days. BCAA supplementation increased the plasma BCAA concentration during exercise, whereas plasma BCAA concentration decreased in the low carbohydrate group. These findings suggest that BCAA supplementation may enhance endurance exercise capacity. In a second randomized controlled trial, BCAA supplementation increased nitrogen retention, which reduced the loss of lean muscle tissue during resistance training. According to researchers, BCAAs may be beneficial as an endurance and muscle recovery aid, and support immune function during athletic performance. BCAAs may also be useful in delaying mental fatigue in endurance exercise.