L-arginine is a conditionally essential amino acid, meaning that under normal circumstances the human body can synthesize it to meet its needs.
In the case of a poor diet or intense physical exercise, the biosynthetic pathway cannot produce sufficient amounts of arginine so a part must be supplemented with diet or supplements.
Since it is the only precursor of nitric oxide (NO) and an important precursor of creatine, it is common for athletes and bodybuilders to take arginine as a supplement.
The easiest way to meet the growing demand for arginine is to take high-dose capsules.