Citrulline Malate is not the best known strength sports supplement, but the results of scientific research on it are quite promising. The substance seems to have a positive effect on muscle endurance, allowing you to squeeze more reps from a set. Muscle recovery would also be served with citrulline malate.

Key points:

1. Citrulline malate is an amino acid that is gradually converted in the body to L-arginine, the amino acid from which enzymes release nitric oxide (NO).

2. Nitric oxide dilates blood vessels and thereby potentially increases the supply of oxygen and nutrients to the muscles during strength training. According to three studies, strength athletes can get more reps from their sets as a result. According to one study, this also allows people to recover faster.

3. Citrulline Malate does not appear to affect maximal strength – only muscle endurance, and possibly aerobic endurance to some extent.

4. For optimal results, take 6 to 8 grams 30-45 minutes before training. The effect of citrulline malate is usually only noticeable after a few to fifteen days.

5. When purchasing, please note that the L-citrulline to malate ratio is 2:1.

6. Citrulline malate supplementation may also help with erectile dysfunction, albeit not as effective as traditional erection drugs.

WHAT IS CITRULLINE MALATE?

Citrulline Malate is the malic acid version of citrulline, a naturally occurring non-essential alpha amino acid.

As a reminder, amino acids are the building blocks of protein and play an important role in building and maintaining muscle mass. In principle, the body can produce non-essential amino acids itself.

Citrulline is not one of the 20 standard amino acids as it is not directly used in tissue protein formation. In other words, it is not a proteinogenic amino acid.

Citrulline is present in many fruits, but especially in watermelon. In this fruit, the connection was first demonstrated in 1930. ^[ i ]

To understand how citrulline malate works, we need to look at its two separate components: citrulline and malic acid.

CITRULLINE

Citrulline is a so-called precursor of the semi-essential amino acid arginine. This means that in the body (namely: in the liver) citrulline can be converted into arginine (for the chemists among us: via ornithine and aspartic acid to argino-succinic acid).

Arginine is known as NO booster. NO stands for Nitric (mon) Oxide (nitrogen monoxide), which plays a role in, among other things, the widening of blood vessels so that more oxygen can be moved, for example to the muscles for more energy. As a result, NO boosters are popular as supplements to provide a greater ‘pump’ during exercise and thereby promote muscle growth. In the next section we will discuss the (alleged) positive effects of supplementation with arginine in more detail.

About the additions ‘L’ and ‘D’
For the record: arginine usually means L-arginine (the addition ‘L’, which stands for ‘Levo’, is usually also used with commercial names of supplements). In addition to the L variant, there is also D-Arginine (with ‘D’ for ‘Dextro’). D-arginine is the form of arginine which, unlike the L version, does not occur naturally in food and in the proteins of the human body. The body does little with D-arginine and therefore this form of arginine is not offered as a supplement.

We also know the addition ‘L’ with citrulline. This refers to the natural form of citrulline. And there is also a D variant that has no nutritional value and is therefore only useful for research in a chemical laboratory. We also know citrulline malate, in which L-citrulline is linked to a molecule of malic acid (malate). Citrulline malate is therefore a compound and not a mixture, something that is important to know when purchasing the supplement (see also ‘Purchase’ below).

MALATE

Malate is the salt form of malic acid, which gives fruits their sour taste. Malic acid is released during the citric acid cycle. It inhibits the production of lactic acid in working muscle cells but stimulates the production of the energy supplier pyruvate.

The addition of malate to supplements such as creatine, but also citrulline, increases the effectiveness of these supplements. ^[ ii ]

Summary
Citrulline malate is a dietary supplement derived from the naturally occurring amino acid citrulline. Citrulline is converted in the body into L-arginine, a so-called NO booster, which widens the blood vessels, so that more oxygen can be moved, for example to the muscles for more energy. Adding malate should increase the effectiveness of the supplement.

CITRULLINE AND ARGININE: WHAT EXACTLY IS THAT?

Citrulline is thus converted into arginine. Supplementation with arginine is attributed various positive effects, in many areas. For example, it is said to stimulate immune function and reduce the occurrence of post-operative infections. ^[ iii ]^[ iv ] Arginine supplementation is also often used in erectile dysfunction, as a milder (and over-the-counter) alternative to Viagra and co. Because arginine increases the nitric oxide level in the blood, the walls of the blood vessels relax, improving blood flow throughout the body, including the erectile tissue in the penis. In addition, arginine increases the nitrite oxide level, which makes the arteries more elastic. ^[ f ]And because nutrients and oxygen are transported to the organs more quickly via the blood, arginine is also said to benefit sexual stamina. ^[ vi ]

Do not use citrulline malate in combination with other erection drugs such as Viagra, Cialis and Levitra.

In summary:
Arginine supplementation can boost immune function. In addition, arginine is used as a mild erection agent.

ARGININE FOR STRENGTH ATHLETES

Strength athletes can also benefit from increased arginine levels in their bodies, although the scientific evidence for this is still shaky. Arginine is an amino acid that is released during the breakdown of proteins. An end product of that degradation is ammonium. A lot of ammonium in your blood makes you tired and inhibits the conversion of glucose into energy. Arginine supplementation helps your body remove the ammonium from your blood more quickly. ^[ vii ]Another common reasoning is that arginine as a NO booster stimulates nitrogen production, thus widening your blood vessels, and wider vessels means more blood and ergo oxygen and nutrients can be transported to your muscles and more lactic acid can be removed. As a result, arginine is said to promote performance, muscle recovery and thus muscle growth. A Brazilian study from 2010 showed that strength athletes who take 3 grams of L-arginine per day achieve more results from their training in terms of lean body mass. ^[ viii ] For that reason, L-arginine is often found in pre-workout supplements. However, other studies show no effect of L-arginine supplementation on strength performance. ^[ xviii]

It is also not certain whether and to what extent arginine increases the endurance of athletes in general. Studies contradict each other. ^[ ix ]

According to a 2014 Russian study, arginine supplementation with 3 to 4 grams per day would prevent muscle breakdown ^[ x ] , something that can be useful when you are cutting. However, the study was conducted on rats and not on humans.

The fact that arginine is not very convincing as a strength sports supplement in the scientific literature is probably because the liver breaks down arginine quickly. As a result, it is only absorbed by the body to a limited extent. According to animal studies, about 40 percent of the amino acid in the liver is destroyed. ^[ xi ]

In summary:
Supplementation with a few grams of arginine per day would increase blood flow to the muscles and allow for more intensive workouts. Opposite every study that shows this is a study in which arginine does not work. This is probably because the liver breaks down arginine quickly.

CITRULLINE INSTEAD OF ARGININE

Some supplement makers solve that problem by not putting L-arginine in their products, but L-citrulline. The liver cannot break down L-citrulline, but enzymes in the body can convert L-citrulline into L-arginine. ^[ xii ] About 83% of oral citrulline appears to be absorbed by the kidneys, where it is converted to arginine. ^[ xiii ] Researchers at the American South Central Agricultural Research Laboratory in Nutrition already demonstrated in 2007 that taking 1 or 2 grams of citrulline per day increases arginine levels by 12 and 22 percent, respectively, after three weeks. ^[ xi ]

Thus, L-citrulline supplementation is a more effective way to introduce arginine into your body than L-arginine supplementation. Still, according to a Japanese study, a good NO booster would best contain a combination of L-arginine and L-citrulline rather than one of the two amino acids alone ^[ xiv ] . But that aside, because this article is essentially not about NO boosters, but about the supplement citrulline malate.

In summary:
L-citrulline supplementation is therefore a more effective way to introduce arginine into the body than L-arginine supplementation.

THE EFFECTS OF CITRULLINE MALATE

Citrulline malate may work in three ways, namely by

stimulating ATP production (ATP is the main source of energy for muscles);
removing waste products such as lactic acid and ammonia from the blood;
stimulating creatine phosphate recovery after exercise.

The most commonly claimed effects of citrulline malate supplementation are:

improving aerobic endurance;
improving muscle endurance (more precisely: you can do more reps);
reducing muscle soreness after training.

Let’s take a look at what (scientific) research is known to support these claims. For the record: we focus on research specifically into supplementation with citrulline malate, not into arginine supplementation (see previous section), although these partly run parallel because citrulline is converted into arginine in the body. Something that is also apparent from the non-sports-related effects of citrulline, such as the positive effect on obtaining an erection. ^[ xv ]

AEROBIC ENDURANCE

Energy delivery in muscle tissue takes place by splitting the ATP (phosphate compound) present. The type of energy source that is used for this depends on the duration and the intensity of the ‘work’. There are three systems that can supply energy: ATP + CrP, the anaerobic system and the aerobic system. ATP + CrP provides energy at lightning speed, but only for a short time (0 – 10 seconds). The anaerobic system is there for efforts of 10 seconds to 3 minutes. During long-term activities (>3 minutes) the body switches to the aerobic system.

According to a 2002 study, citrulline malate provides more aerobic energy or more endurance. ^[ xvi ] It has been found to increase ATP production by 34%. The production of phosphocreatine needed to make new ATP increased by 20% during rest. The study participants were found to experience significantly less fatigue when citrulline malate was taken.

In a 2016 study, citrulline malate was tested on 22 trained men who each cycled 4 kilometers on an exercise bike. The citrulline users not only covered that distance faster, they also suffered less from muscle fatigue afterwards. ^[ xxvi ]

Research from 2010 conducted among cyclists suggests that citrulline malate produces more growth hormone. ^[ xxii ]

You will understand that these possible effects of citrulline malate are especially beneficial for endurance athletes. It is not without reason that citrulline was a popular supplement in cycling in the 70s and 80s. Despite this, the amount of scientific evidence for effects on aerobic performance is still quite scant.

In summary:
Supplementation with citrulline malate appears to improve aerobic performance (long-endurance activities) and reduce associated fatigue. However, the amount of research on this is still limited.

MUSCULAR ENDURANCE

The main claimed effect of citrulline malate for strength athletes is to increase muscle endurance. A handful of studies seem to support this effect.

American research from September 2015 shows that citrulline malate increases the maximum number of repetitions during a leg workout. ^[ xvii ] For strength athletes who take 8 grams of citrulline malate before training, the number of reps they can get from their sets increases by as much as 9 percent, according to the results of the study, conducted among 12 experienced strength athletes, each time during a leg training.

A similar study from 2010, but then based on chest training, also found that you can do more repetitions thanks to supplementation with citrulline malate. ^[ xviii ]

A study from the end of 2015 examined women specifically in the bench press and leg press. Again, the participants were shown to be able to produce a greater number of repetitions when they had consumed citrulline malate (8 grams each, one hour before training), especially when pushing the leg. ^[ xix ] The number of ‘extra’ reps turned out to be even greater than that in men in the other two studies. The researchers therefore raise the possibility that women respond better to citrulline malate than men. Women have more estradiol (a sex hormone belonging to the estrogen group) in their blood than men, and there may be a synergy between estradiol and citrulline malate. ^[ xx ]

What is striking about the aforementioned studies is that it has remained unclear which aspect of citrulline malate is responsible for the increase in the number of repetitions. Although the supplementation improved performance, it had no effect on the concentration of lactic acid in the blood, heart rate and blood pressure. The researchers therefore state that further research is needed to find out.

The 2010 study also showed that the participants suffered less from muscle pain afterwards. ^[ xviii ] This means that citrulline may improve recovery between workouts, probably by boosting creatine phosphate levels in the muscles. However, one study is far too little to make firm statements about this.

Although the above studies sound promising, a fourth study, published in November 2017, has shown no effect of citrulline malate in strength training. The supplement was tested on twelve recreational male strength athletes. During two sessions they had to do five sets of bench presses until muscle failure and were given either 8 grams of citrulline malate or a placebo beforehand. The researchers found no benefits of using citrulline malate with regard to exercise performance and muscle pump, nor with regard to focus, energy and fatigue. ^[ xxv ]

Finally, there is no evidence that citrulline malate also improves maximal strength, as creatine does, for example.

In summary:
Supplementation with citrulline malate may improve muscle endurance. Nitric oxide erodes blood vessels and is said to increase the supply of oxygen and nutrients to the muscles during workouts. This allows you to get more reps out of your sets. To date, three studies have shown this, while one study showed no effect of citrulline malate. One study suggests that citrulline malate also promotes muscle recovery.

USE, DOSAGE AND TIMING

The dosage of citrulline malate depends on what you want to use it for.

Some men mainly use it as an erection agent and 1500 mg per day is already sufficient. ^[ xv ]

For endurance athletes who want to improve their performance and reduce muscle fatigue, 2400 mg is enough, to be taken one hour before training. ^[ xxvi ]

In strength sports, a dose of 6 to 8 g seems to be required, to be taken 30-45 minutes before training. ^[ xxvii ] According to some supplement manufacturers, you can also spread the dose, for example 3 grams before training and 3 grams during training.

On non-training days, the time of intake does not matter much. It is sometimes recommended to take citrulline malate on an empty stomach, but there is no evidence of its benefit.

Since citrulline malate has a fairly strong, sour taste, you can choose to take it with fruit juice.

Citrulline malate is increasingly found in ready-to-use pre-workout supplements. Usually citrulline malate in it is dosed too low to have any effect.

In summary:
For strength sports: take 6 to 8 grams of citrulline malate, 30-45 minutes before training.

DOES IT WORK RIGHT AWAY?

Do not expect an immediate effect from citrulline malate. In some people it can take up to 15 days before an effect is noticeable. Others notice ‘something’ after a few days. ^{[ xxiii ][ xxiv ]}

Most studies have also shown that a minority of users do not notice anything at all from supplementation with citrulline malate. The practical score is estimated at 8/10.

There are no known harmful effects of long-term citrulline malate supplementation. So you don’t have to ‘cycle’ the supplement, although you can of course do that.

In summary:
Citrulline malate does not work immediately, but usually within fifteen days. Some already notice an effect after a few days of supplementation.

SIDE EFFECTS

There are no known serious side effects of citrulline malate.

The 2010 study cited earlier, which found an increase in the number of reps in chest training, revealed a mild side effect: 15 percent of participants complained of abdominal pain. ^[ xviii ] Therefore, take citrulline malate with sufficient liquid (water or fruit juice).

Do not use citrulline malate if you are taking erection drugs like Viagra or nitrates for heart disease. Interaction with those drugs can cause a dangerous drop in blood pressure.

In summary:
There are no known serious side effects of citrulline malate.

BUY CITRULLINE MALATE

Got excited about citrulline malate, whether or not because of the rather promising research results? Then you can purchase it as a separate supplement from the better supplement store for roughly 8 to 10 euros per 100 grams, in powder form. Citrulline Malate is also available in capsules.

There are two criteria to consider when purchasing this supplement:

It must provide a chemically bound source of L-citrulline and malic acid (malate). In other words, every molecule of L-citrulline is directly bonded to every molecule of malic acid. Powders in which one puts the individual compounds first and then mixes them together are not the best choice. This cannot always be deduced from the label, so it is better to buy your stuff from a reputable (web) store.
The ratio of L-citrulline to malate should be 2:1. This is the ratio used in most studies. Not infrequently, for cost savings, a 1:1 ratio is offered.

Pay extra attention to these criteria when citrulline malate is part of a pre-workout product.

In summary:
Only buy citrulline malate from a reputable (web) store or manufacturer, and check whether the ratio of L-citrulline to malate is 2:1.

IN SUMMARY