L-arginine supplements may be the second most popular fitness and energy supplements (next to protein) found in the gym bags of body builders, weight lifters and everyday athletes, as it is used most often to promote healthy lean muscle development. How? Arginine is needed by your body to make nitric oxide, a substance that allows your blood vessels to dilate. This action allows your muscles to receive the oxygen and energy needed to perform and to grow. Arginine also helps your body remove excess ammonia, support healthy immune function and promotes the secretion of several hormones, including glucagon, insulin and growth hormone.