Arginine vs Citrulline – Which of the 2 is better?


During your time in the gym, you will hear all sorts of statements about the effectiveness of certain supplements and the uselessness of others.

One of the hot topics of debate is whether arginine is more effective at promoting muscle growth than citrulline or vice versa.

Both compounds are amino acids that ensure numerous physiological functions in the body, and while the body converts citrulline into arginine, there is more to the story.

In this article, we will discuss how each amino acid promotes muscle growth and which one is more effective.

How does arginine stimulate muscle growth

L-arginine is a semi-essential amino acid that gets produced by the body during certain situations (e.g., trauma, sickness, pregnancy).

L-arginine promotes the production of nitric oxide, a molecule indispensable for the expansion of blood vessels and the functioning of the cell’s powerhouse.

The main purpose of taking L-arginine during workouts is to improve blood flow to the muscles, which significantly optimizes your performance.

Several studies found that L-arginine promotes the production of human growth hormone (HGH), which initiates the process of muscle repair.

Learn more about L-arginine.

How does citrulline stimulate muscle growth

Citrulline is a non-essential amino acid that your body can produce naturally.

Despite this, researchers found that increasing the levels of citrulline by taking dietary supplements can yield additional health benefits, especially for fitness.

Interestingly, citrulline doesn’t take part in the process of protein synthesis; however, this doesn’t undermine the health benefits of this compound.

After taking L-citrulline, the kidneys convert it into L-arginine, which gets converted to nitric oxide.

Learn more about L-citrulline

Muscle growth – Arginine Vs Citrulline

To determine the superiority of one amino acid over the other, we need to look at several aspects.

Over dozens of studies found that L-citrulline is better absorbed in the intestines relative to L-arginine. In fact, one study conducted on mice found that only 30% of the supplemented arginine escaped the first-pass metabolism (FPM), which is a process that takes place in the liver.

In other words, if you take 10 grams of L-arginine supplements, only 3 grams will reach peripheral circulation.

Conversely, citrulline increases the concentrations of arginine by up to 63%. Researchers attributed this increase to the conversion of citrulline into arginine in the kidneys. Moreover, some evidence suggests that most cells are able to perform this conversion when the right enzymatic machinery (e.g., argininosuccinate synthase and lyase) is available.

According to one study, consuming citrulline supplements elevates arginine levels more than taking arginine.

Why choose L-citrulline?

After reading this information, you might be questioning the utility of taking citrulline if it will end up getting converted to arginine.

While this question is legitimate, taking citrulline supplements carries another purpose, which is to increase the levels of arginine significantly.

Based on some evidence, researchers believe that most cells of the body can convert citrulline into arginine, which allows for further use of this amino acid.

Once the conversion has occurred, arginine will take part in a metabolic reaction that ends with nitric oxide as a final byproduct.

This molecule interferes with complex cellular cascades of the smooth muscles surrounding blood vessels. As a result, the muscle fibers relax, leading to the vasodilation of vessels.

Since the skeletal muscles have a rich network of blood vessels, this means that they will benefit from substantial blood flow.

The improved blood perfusion allows for better delivery of nutrients and oxygen, as well as hypertrophy-inducing hormones (e.g., HGH, IGF1).

Because most arginine gets lost before reaching the peripheral circulation, citrulline leads to a superior activation of the NO cascade. Consequently, you can expect better muscle hypertrophy after taking citrulline supplements.

After demonstrating the superiority of citrulline over arginine, let’s see what you can expect from supplementing your body:

Better athletic performance

As the blood vessels inside your muscles expand in diameter, more oxygen will be available for aerobic training. The oxygen gets incorporated into the Krebs cycle to generate energy in the form of ATP. This molecule is indispensable for the contraction of muscles.

For this reason, people who take citrulline supplements report better performance and less fatigue in the gym since this amino acid also aids in the elimination of ammonia – a primary trigger of muscle fatigue.

Better pump in the gym

Similar to athletic performance, more blood flow to the muscles allows you to lift heavier weights and do more repetitions during strength training. You can think of this benefit as an indirect way to promote muscle hypertrophy.

For instance, instead of doing 10 reps per exercise, you might be able to push yourself until the 15th repetition, which causes the muscle fibers to tear. While this sounds scary, it is exactly the purpose of training in the gym. You want the muscle fibers to be torn microscopically, which stimulates the release of growth hormones.

Lower blood pressure

The expansion of blood vessels inadvertently lowers blood pressure. The regulation of blood pressure is crucial for people susceptible to chronic blood hypertension – a disease that could negatively impact your fitness journey.

Therefore, you will be taking advantage of the vasodilatory properties of citrulline in promoting muscle growth and preventing blood hypertension.

Before taking any of these supplements, make sure to speak with your primary care physician to avoid any health complications.

Arginine vs Citrulline conclusion

The research examining the superiority of arginine vs citrulline over one another is scarce; however, all the available evidence suggests that citrulline is more potent at inducing vasodilation, which is the primary process that both amino acids use to promote muscle growth.

Hopefully, this article managed to highlight how taking citrulline supplements yields better results in terms of performance and muscle hypertrophy.

If you still have any questions about the two amino acids, please don’t hesitate to check our separate blog posts covering the effects of arginine and citrulline.

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