L-Arginine is a conditional amino acid, meaning it’s only considered essential in time of illness and stress. You can often find L-Arginine in a pre workout supplement for this reason. When we workout, we put our bodies under stress. L-Arginine is a precursor to nitric oxide, L-Arginine is consumed it is converted to nitric oxide in the body. This in turn, helps promote muscle development, recovery, and blood flow.