L-citrulline is a nonessential amino acid that is obtained from diet and is also produced in the body, mainly from glutamine. One of the best known diet sources is watermelon; 1 cup diced seedless watermelon has about 365 mg citrulline. Approximately
Approximately 80% of the body’s citrulline is converted in the kidneys into arginine, another important amino acid. Arginine is then converted to nitric oxide, which is known to be a potent dilator of blood vessels. Many believe this process of conversion of citrulline into nitric oxide could serve as an ergogenic aid. In fact, it is thought the consumption of citrulline might be a more efficient way to raise blood levels of arginine than consumption of arginine alone because more citrulline is absorbed from the gut than arginine. This is one reason why injections either IV or IM/SQ, of citrulline or arginine are thought to be more a effective way of providing this amino acid than orally.
Most studies have shown the use of citrulline malate, a combination of citrulline with malic acid (a component in many fruits that is also produced endogenously), because malate, an intermediate in the Krebs cycle, might enhance energy production.
With all research there are studies both with significant and limited results. There are research studies to support supplemental citrulline works as an ergogenic aid. Studies range from 1 to 16 days with 8 grams of citrulline malate and others used 3g grams before testing and 9 gram over 24 hours. Both noted improvement during exercise such as bench press and the reduction of muscle soreness 1 to 2 days post workout. Citrulline supplementation may increase plasma levels of nitric oxide metabolites and thus supplementation may directly cause an improvement in athletic performance.
When taken orally, citrulline supplementation may cause GI upset. Most report no side effects from injections either IV, IM or SQ.