If optimizing your workout and supporting overall performance in and out of the gym is what you want, then try L-Arginine, an essential amino acid. As an essential amino acid, L-Arginine is one of the building blocks of protein. L-Arginine also supports immune function and the effects of a healthy exercise program. When trying to make the most out of your gym membership, add 21st Century's L-Arginine supplement to your gym bag.