GNC L-Arginine (90 Tablets) increases nitric oxide production for improved blood flow in the muscles, fueling their growth and repair. Arginine is involved in creatine formation and the synthesis of creatine provides energy to your muscles for movements, especially quick movements. Increases Nitric Oxide Production: Arginine is an essential precursor of nitric oxide and L-Citrulline can be recycled in the Citulline - NO cycle. This way both contirbute to Nitric Oxide Production. Helps Maintain Blood Vessel Tone: Arginine and Citrulline both lead to production of nitric oxide and nitric oxide help maintain blood vessel tone and thus plays a role in protein synthesis.