L-arginine, like other amino acids, plays a role in building protein. The body can use the protein to help build muscle and rebuild tissue. In addition to building protein, L-arginine releases nitric oxide in the blood. Nitric oxide causes blood vessels to open wider for improved blood flow. Increased nitric oxide enhances exercise performance by improving blood flow and oxygenation to the muscles. L-arginine also stimulates the release of growth hormone, insulin, and other substances in the body.