Arginine is a semi-essential amino acid. It is a building block of protein that performs a host of physiological functions including hormone secretion, an increase in growth hormone output, the removal of toxic waste products from the body, and immune system defenses. It is a known precursor of the gas nitric oxide [NO2]. Arginine presents benefits to athletes. Supplementing with Arginine may boost the immune system, thereby allowing the athlete to train harder and avoid the detrimental effects of minor illnesses associated with overtraining.