L-Arginine also plays a key role in the release of nitric oxide (NO) into the blood, which widens blood vessels, increases muscle oxygenation, and results in a more efficient muscle gain and repair cycle.
At sufficiently high intakes, this amino acid results in increased human growth hormone (HGH) levels. HGH stimulates muscle growth. It is also vital in the synthesis of creatine. Trials combining weight training with L-Arginine have shown decreases in body fat and increases in total strength and lean body mass, vs a placebo group.
L-Arginine may also aid in supporting erectile / sexual dysfunction through this same mechanism of widening the blood vessels. As a booster of immunity, it stimulates the thymus and promotes lymphocyte production. This leads to L-Arginine's ability to promote healing of burns and other wounds.