L-Arginine is a conditionally essential amino acid and is a precursor for the production of Nitric  Oxide. L-Arginine has been shown to promote increased nitric oxide which supports muscle development and recovery.

L-Citrulline is one of the three dietary amino acids in the urea cycle, alongside L-Arginine and L-Ornithine. Taking L-Citrulline increases plasma levels of ornithine and Arginine and improves the ammonia recycling process and nitric oxide metabolism. Consequently, it is used in areas where nitric oxide is relevant, namely athletic performance, and vascular health, and erectile dysfunction.