L-arginine, an amino acid, is a supplement that’s famous in the fitness world for its conversion into nitric oxide. On paper, nitric oxide increases blood flow and dilates the blood vessels. Theoretically, this will cause the muscle to swell and leads to a tightening sensation called “muscle pump”. But what is true on paper isn’t always true when put to practice. Let’s look into the science!

Conflicting Results

There aren’t many studies performed on humans and the few that exists today show conflicting results. Oral intake of l-arginine on adults, together with a structured training regime, lead to a small increase in fat-free mass, compared to the placebo group which only received training and no l-arginine. However, no increase in blood flow was noted. (1)

When tested on people with blood flow disease, l-arginine reduced pain and discomfort, as it appeared to increase blood flow to the muscles. (2)

No Effects on Nitric Oxide in Healthy Humans!

A daily intake of AAKG (a popular supplement that contains mostly l-arginine) in physically active men failed to increase blood flow or heart rate. The author didn’t see an increase in nitric oxide in the participants which means that AAKG also failed to convert itself into nitric oxide. (3)

When ingested, the amount of l-arginine in the blood increases, but the supplementation has no effect on nitric oxide production, protein synthesis or performance in anaerobic capacity in well-trained male athletes. (4-5)

Rats and Muscle Loss

Positive effects are seen in studies with rats where l-arginine is associated with improved aerobic capacity and prevention of muscle loss. (6) No surprise there, adding amino acids (protein) limits muscle loss. This effect would probably be seen with any protein source, as arginine is a non-essential amino acid (meaning that the body can makes it from carbs).

L-arginine appears to have an effect of increased nitro oxide, thus increased blood flow to the muscle, in non-healthy individuals and rats. Unfortunately, this effects doesn’t seem to appear in healthy individuals.

Skip Arginine the Supplement

If you are healthy and human (which we hope you are), you probably have no benefit of wasting your money on L-arginine supplements. Even though l-arginine is a non-essential amino acid, the body needs more of it in times of illness (a so called conditionally essential amino acid). Still, l-arginine is commonly found in the diet which means that you don’t have to take supplements to get the daily recommended dose of arginine, even when you are sick.

Article by Maria Ekblom, licensed physiotherapist and personal trainer.

Sources (PMID):

1. 22553931

2. 9809945

3. 21813912

4. 18708287

5. 21191143

6. 28987235