Does citrulline improve lifting performance?
Citrulline (commonly taken as citrulline malate) is known for its performance-enhancing potential. However, the literature on citrulline is mixed, with some studies showing benefit, and others not. Paradoxically, this occurs despite similar citrulline doses (8 grams) and timing (~30-60 minutes pre-workout) across studies.
Luckily, Trexler et al.’s 2019 meta-analysis clarifies citrulline’s role in performance. In this analysis of 12 studies, citrulline modestly improved strength endurance (based on 8 studies), while marginally enhancing power outcomes.
Indeed, citrulline showed greater benefit for strength endurance (effect size= .30), as compared to power outcomes (ES of .04).
In what context does citrulline work well?
Importantly citrulline can help no matter your training status. More specifically, citrulline provides modest benefit for both untrained and trained lifters (ES= .18 and .21, respectively). Likewise, citrulline can improve performance on any movement. In fact, citrulline improves lower (ES= .17) and upper body strength (ES= .21) gain similarly.
What's more, citrulline can help with short and long rest intervals alike. Indeed, citrulline has shown to improve strength endurance in studies with short (~1 minute) and long (2-3 minute) rests between sets.
All considered, if you're lifting weights for 6+ reps, citrulline can improve performance.
Just how beneficial is citrulline?
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.
Can citrulline enhance muscle gain/1RM?
To be clear, strength endurance/work capacity is “total repetition performance across multiple sets to failure”. This considered, we can’t say whether or not citrulline supplementation improves 1RM/maximal strength.
Similarly, we don’t know if improved strength endurance translates to greater muscle gain. Nevertheless, we can speculate.
First speculation: citrulline allows for greater work performance, which improves muscle growth over time. In essence, this is how creatine increases muscle gain.
Second speculation: If the first speculation is true, then citrulline can also improve maximal strength performance. This is because greater muscle size augments long-term strength gain. Otherwise, citrulline may directly improve 1RM.
That said, the above hypotheses are yet to be studied. Citrulline may improve muscle growth and 1RM over time, but we simply lack data here.
Is citrulline worth taking?
This decision comes down to personal preference. Personally, I despise citrulline malate’s taste, so the cost isn’t justified. Moreover, there’s no evidence that citrulline actually improves muscle/strength gain. However, if you like the taste and have some extra money to spend, then go for it. At worst, citrulline is a slight disappointment, but it might improve gains.
How to take citrulline?
To benefit most, you should take 8-9 grams of citrulline malate (or 4.5-5 grams of citrulline), 1-2 hours pre-workout.
Fun fact: Watermelon contains .7-3.6 mg of citrulline per gram of fresh weight, so you can swap citrulline for 220-1,000 grams of watermelon (if desired).
Why does Citrulline show no benefit in many studies?
As a more general research point, when a supplement provides a small effect, it can be hard to detect in any one study/RCT. For example, many studies fail to find greater lean mass/strength gains with protein supplementation. However, when Morton et al. (2017) pooled all data for a meta-analysis, protein’s beneficial effects were revealed.
This also happened in Trexler et al.’s (2019) meta-analysis. Though some studies were underpowered, and others favored control, the data supported citrulline supplementation when taken together.
This article is a guest blog post by Vincent Sparagna.
Trexler’s literature review: https://www.ncbi.nlm.nih.gov/m/pubmed/30895562/
Trexler’s article on citrulline and mechanisms of action:
Papers on other supplements’ effect sizes:
Caffeine, bicarbonate, beta-alanine, and nitrate:
Creatine supplementation increases lean mass gain by ~1-2 kg over 4-12 weeks, as compared placebo: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2048496/
Greater muscle size seems to augment long-term strength gains: https://link.springer.com/article/10.1007/s40279-019-01107-8
Watermelon contains citrulline:
Morton et al., 2017: https://www.ncbi.nlm.nih.gov/m/pubmed/28698222/
Studies with short/long rest intervals finding ergogenic benefit to citrulline: