Citrulline malate is a supplement that is typically used to increase strength and endurance. The main benefit of it is to increase nitric oxide levels, which can improve blood flow to muscles.
What is Citrulline Malate?
Citrulline malate contains L-citrulline bonded with malic acid.
L-Citrulline is an amino acid that gets converted by the body into L-arginine. Arginine is converted into nitric oxide, therefore increasing blood flow.
Citrulline malate enhances creatine phosphate regeneration – meaning quicker recovery between sets. Research doesn’t appear to support that this happens for L-citrulline alone, so this aspect is attributed to the malic acid.
The reason why citrulline malate is used instead of arginine supplementation is that it actually raises blood arginine levels more effectively than arginine supplementation. This is because arginine is more poorly absorbed. Taking high enough dosages of arginine to reach appropriate levels is possible, but often leads to GI distress.
Citrulline Malate increases blood levels of ornithine and arginine and improves nitric oxide metabolism and the ammonia recycling process.
This increases lactate and ammonia clearance following exercise. For lifters, this appears to have a carryover effect for people doing multiple sets of an exercise. While the first set might only have a mild improvement, if any at all, the later sets might show a much more noticeable improvement.
This ammonia-buffering effect reduces acidosis during exercise and also helps reduce delayed onset muscle soreness (DOMs) noticeably.
Citrulline Malate also improves ATP production following exercise, which is another aspect as to why it might help over multiple sets. Malic acid is an intermediate in the citric acid cycle, which is how it is theorised to help with this process.
The main implications of supplementation appear to be the ability to add an extra couple of reps here and there while resistance training. There potentially could be benefits for supplementing citrulline malate for endurance performance, but there isn’t a lot of research to support that view at this stage.
It’s also unclear whether adding citrulline malate into other supplements provides an additive effect. Caffeine, creatine and beta-alanine supplementation each individually could provide benefits for lifters.
As a hypothetical example, each of those options individually provides something like a 1-3% boost in performance. Does adding all 3 together equal result in a >3% boost in performance? Or does it top out at some stage?
I have the same thought process when it comes to adding citrulline malate into the mix. Other people have theories about whether potentially some of these ingredients might inhibit the effects of each other in some way. Either way, I’m yet to see strong research supporting adding citrulline malate to other supplements providing some form of synergistic effect, so it is a watch this space area.
Thoughts on the Mixed Results
It has been interesting watching the research evolve over the years. Up until 2016, the research was mostly promising for citrulline malate. Since then there have been some studies showing poor results. The ones that I’m aware of are:
- Citrulline malate supplementation does not improve German Volume Training performance or reduce muscle soreness in moderately trained males and females
- Acute effect of citrulline malate supplementation on upper-body resistance exercise performance in recreationally resistance-trained men
- The effect of l-citrulline and watermelon juice supplementation on anaerobic and aerobic exercise performance
- The effect of citrulline malate supplementation on muscle fatigue among healthy participants
If you look at any of those studies individually without context, it will look like citrulline malate supplementation was ineffective.
When you look at it in the context of the overall body of research, there is a different conclusion.
In general, the studies produce results that are relatively small. This is pretty normal for supplements. No sports supplements are producing massive improvements in performance across the board.
When looking at the overall body of research, citrulline malate appears to produce improvements in line with the results that caffeine and beta-alanine produce, on average. Both of those are considered to be evidence-based supplements that consistently produce good results, so I would add citrulline malate into that category as well.
To quote a 2019 meta-analysis by Trexler et al on citrulline supplementation: “In this analysis of 12 studies, citrulline modestly improved strength endurance (based on 8 studies), while marginally enhancing power outcomes. This occurs in both trained and untrained lifters.
An effect size of .3 for strength endurance highlights a small-modest benefit, but we should examine this effect in context.
For comparison, creatine supplementation yields an ES of .42 for upper, and .21 for lower body strength. Meanwhile, similar supplements log effect sizes of .41 (acute caffeine), .40 (bicarbonate), .19 (nitrate), and .17 (beta-alanine) for 45 second-8 minute exercise performance. As such, citrulline malate provides effects comparable to those of other ergogenic supplements. Therefore, citrulline probably won’t make a major difference, but it might help.”
Thoughts on Whether This Will Impact a One-Rep Max
The research indicates that citrulline malate improves total reps across multiple sets. And these sets likely need to be taken near failure for the effects to be seen.
As a powerlifter, this topic interests me, but theoretically, there is no direct way that citrulline malate would increase a person’s 1RM.
It could be argued that citrulline malate could increase muscle hypertrophy due to the increased reps that are able to be completed in each set. Then, in turn, that added muscle could contribute to a higher 1RM.
As far as I am aware, there is no solid data on this topic yet to even support the hypothesis that citrulline malate could increase hypertrophy.
Thoughts on Citrulline Malate & DOMS
Along with potential performance-enhancing benefits, citrulline malate supplementation may also help reduce delayed onset muscle soreness or “DOMS”.
One study where participants were made to consume either 500ml of watermelon juice (1.17g of l-citrulline) or enriched watermelon juice (4.83g of added l-citrulline in addition to 1.17g already in it), found that both options reduced muscle soreness 24 hours later. This was in comparison to having watermelon juice with no citrulline.
There are two proposed mechanisms for this are:
- Citrulline facilitates the clearance of ammonia. This results in a reduction of lactate accumulation in the blood. Although, lactate does not seem to be a significant contributor to muscle soreness.
- Citrulline increases nitric oxide. Nitric oxide is involved in muscle contractile function and repair which could explain the reductions in muscle soreness. Potentially more so than the first proposed mechanism.
A systematic review looking at 13 total studies on the topic found that citrulline made a significant difference to DOMS.
Why Citrulline Malate and Not Just Citrulline?
From one perspective citrulline malate is by far the most researched form of citrulline. That alone is enough to make me prefer it. We know that it has benefits in this form, while we are less sure about how much benefit you get from L-Citrulline alone.
There is also speculation that malic acid has independent performance benefits related to ATP production.
Being realistic though, it does appear that most of the benefits come from the citrulline itself. But citrulline malate is relatively cheap and widely available.
The only way I could see that citrulline malate would be inferior to L-citrulline is if the ratio of citrulline to malic acid is low, or if the total dosage is too low. It appears that a 2:1 ratio of citrulline to malate seems solid.
Frustratingly enough though, it is worth being aware that some companies have misreported their dosages in the past (based on US data). In one study, five different products that claimed to have a 2:1 ratio actually had anywhere between a 1:1 and 1.9:1 ratio.
To the best of my knowledge, there is nothing to indicate a lack of safety when utilised by healthy people at the effective dosages that have been studied.
No long-term studies have been done though, so this might change in the future.
The dosage I would recommend is 8g citrulline malate (with a 2:1 ratio of citrulline to malic acid) taken 30-120 minutes prior to training.
Peak arginine levels appear to be reached 1.4-2.3 hours after supplementation which lines up well with this recommendation.
There is one study comparing timing which reported no difference between consumption one hour or two hours prior to training.
And to put things in perspective since a lot of people also like a food first approach: Watermelon is one of the highest food sources of citrulline. Per 100g, watermelon contains 0.7-3.6g of citrulline. Since the ideal ratio is ~2:1 and the total dosage of citrulline malate is 8g, that means that 5.3g of citrulline is the desired dosage. It would take a minimum 200g of watermelon (and potentially a lot more) to achieve that dosage.
Citrulline malate quite clearly improves performance when taking multiple sets to failure, by allowing additional reps to be completed.
If your goal is to increase the number of reps completed, then it would be worthwhile taking citrulline malate. It’s relatively affordable and doesn’t have any noticeable downsides.
From another perspective, if your goal is hypertrophy or to improve your strength for one rep max attempts, then it is questionable as to whether citrulline malate will help. Personally, as a powerlifter, I don’t use citrulline malate, unless it just so happens to be a part of a pre-workout that I am mainly taking for caffeine. But if the research starts to indicate that it will increase one rep max performance, I would definitely consider it.