Abstract

The BCAAs (leucine, isoleucine, and valine) are essential amino acids able to bypass metabolism in the liver after ingestion and be oxidized directly within skeletal muscle. A consistent state of turnover between protein synthesis and protein degradation exists within skeletal muscle, and the rate of turnover can be accelerated with exercise. Because intense exercise can increase the protein turnover rate, skeletal muscle may require additional intake of BCAAs in the attempt of attenuating muscle protein breakdown following exercise. Moreover, the products of BCAA oxidation include Kreb Cycle intermediates and ketones, suggesting a potential role for protein/BCAA substrate utilization during exercise. The aim of this review was to investigate the existing evidence behind the purported ergogenic benefits of BCAA supplementation regarding muscle protein synthesis, muscular hypertrophy, various aspects of exercise recovery, muscle damage and inflammation, immune system function, and substrate utilization. BCAAs do not appear to augment improvements in muscular strength, power, or endurance with resistance training, but may be able to preserve these muscle characteristics over time during hypocaloric states. However, BCAAs appear to mitigate elevations in indices of muscle damage in response to acute endurance and resistance exercise, regardless of different damage protocols being utilized. Despite enough evidence showing the ability of BCAAs, particularly leucine, to up-regulate muscle protein synthesis, there is no provision towards additional benefit to performance or adaptations to resistance and endurance training with supplementation. In conclusion, peri-exercise BCAA supplementation appears to be most effective only in terms of recovery between exercise sessions and the preservation of both muscle mass and muscle performance under states of hypocalorism.

Keywords

protein synthesis, skeletal muscle, leucine, muscle strength, hypertrophy