Branched-chain amino acid supplementation reduces delayed onset muscle soreness in resistance-trained athletes following intense exercise, but the effect is not observed in endurance athletes and may be confounded by unmeasured protein intake.

After intense resistance exercise, muscle fibers sustain small tears that trigger inflammation and breakdown of muscle proteins. Branched-chain amino acids, especially leucine, enter muscle cells and activate a signaling system that shuts down the machinery responsible for breaking down muscle proteins. This reduces the release of damage signals into the bloodstream and lowers inflammation around the muscle. With less damage and fewer inflammatory chemicals present, pain-sensing nerves in the muscle become less active, resulting in less soreness.