Should I Take L-Arginine Before, During or After My Workout?

Athletes looking for increased muscle size and a boost in exercise performance often turn to dietary supplements like L-arginine. Although some clinical evidence suggests the supplement may be helpful, the mixed results may be a determining factor in your decision whether to try L-arginine, especially since it can be expensive. If you do add L-arginine to your workout regimen, it may be most effective when taken before exercise.

L-arginine is an amino acid your body uses for ammonia detoxification, hormone secretion, DNA synthesis and nurturing the immune system. Good food sources of L-arginine include eggs, meats, milk, soy proteins, peanuts and walnuts, although arginine can also be synthesized in the laboratory. Supplements come in the form of tablets, capsules and powder to be mixed with liquids.

A team at Stanford University in California investigated L-arginine's effects on aerobic capacity in laboratory animals. Their results, published in "Journal of Applied Physiology" in August 2000, demonstrated that mice given L-arginine showed an increase in post-exercise urinary nitrate excretion and aerobic capacity, whereas a control group did not. In healthy mice, L-arginine also enhanced the synthesis of endothelium-derived relaxing factor, a process affecting the thin layer of cells that line the interior surface of blood vessels and promote smooth muscle relaxation.

L-arginine is often promoted as a human growth stimulant; this is one reason it's popular among bodybuilders, who believe it promotes greater gains in muscle mass and strength. However, although arginine given through an IV can lead to increased circulating growth hormone concentration, oral arginine supplements powerful enough to produce the same results are likely to cause stomach discomfort and diarrhea. Physician and medical writer Dr. Ray Sahelian adds that studies have not consistently found pre-exercise oral amino acid enhances growth hormone release, nor does taking L-arginine with other amino acids before strength training increase muscle mass to a greater extent than strength training alone.

Researchers at the University of Exeter in England found that a dietary supplement containing L-arginine could enhance the production of nitric oxide in the body and significantly boost stamina during high-intensity exercise. The study, published in 2010 in "Journal of Applied Physiology," focused on males 19 to 38 years of age who consumed either a beverage with 6 g of L-arginine or placebo one hour before exercise on a cycle ergometer. The results suggested that the group taking L-arginine were able to exercise up to 20 percent longer due to enhanced high-intensity exercise tolerance.

L-arginine has a few reported side effects, including nausea and diarrhea. In higher doses, there may also be a bitter taste. Because it has the effect of dilating blood vessels, low blood pressure may occur in some people. If you have kidney or liver damage, taking L-arginine may cause low potassium and high serum urea nitrogen levels.