How citrulline and watermelon affect performance and recovery for running, OCR, and endurance sports
Thomas Solomon, PhD.
Updated onReading time approx 4 minutes (800 words).
What you’ll learn:
Citrulline is an amino acid found in watermelon, but your body also makes it. It helps run the urea cycle (your built-in waste-removal system) and is a building block for nitric oxide, which widens blood vessels briefly to help nutrients reach muscles.
Taking citrulline before lifting can give you a small boost in reps or power. Whether adding malate (citrulline malate) is necessary is still unclear.
For running and cycling performance, citrulline does not reliably help improve time trials, time to exhaustion, or V̇O2maxV̇O2max is the maximal rate of oxygen consumption your body can achieve during exercise. It is a measure of cardiorespiratory fitness and indicates the size of your engine, i.e., your maximal aerobic power, which contributes to endurance performance..
Curious about the how and why? Scroll down for the details, the nuances, and the nerdy bits.
The information I provide is not medical advice. Citrulline can have side effects and might interact with other drugs, nutrients, and medical conditions (see here). If you are unsure, always consult your doctor to ensure that a specific supplement is safe for you to use.
What is citrulline?
Citrulline is a “nonessential” amino acid, which means your body can make it. It isn’t used to build proteins, but it plays a role in the urea cycle and is made when your body produces nitric oxide (NO). In the urea cycle, your liver’s mitochondria turn ammonia (a by-product of hard exercise) into urea so you can excrete it. For a clear primer on the urea cycle, see this overview and the reaction map here.
2 L-arginine + 3 NADPH + 3 H+ + 4 O2 ⇌ 2 L-citrulline + 2 nitric oxide + 4 H2O + 3 NADP+
You can raise blood citrulline by eating watermelon or by taking supplements like L-citrulline or citrulline malate. Malate is part of the tricarboxylic acid (TCA) cycle (your mitochondria’s ATP-making engine). Some folks think adding malate boosts energy production, but we don’t have strong proof that malate adds benefits beyond L-citrulline on its own. During exercise, the two main ideas are simple: more NO may briefly increase blood flow to working muscles, and better ammonia clearance might delay fatigue. Do those ideas translate to real-world performance? Let’s see…
What is the scientific evidence on citrulline and and watermelon’s impact on athletic performance?
L-citrulline is generally safe to consume for short-term use, though some people report mild stomach upset.
For strength-type efforts, meta-analysesA meta-analysis quantifies the overall effect size of a treatment by compiling effect sizes from all studies of that treatment. show a small improvement in repetitions or power after pre-exercise L-citrulline or citrulline malate (Vårvik et al. 2021, Gough et al. 2021).
For endurance outcomes like V̇O2maxV̇O2max is the maximal rate of oxygen consumption your body can achieve during exercise. It is a measure of cardiorespiratory fitness and indicates the size of your engine, i.e., your maximal aerobic power, which contributes to endurance performance., time to exhaustion, or time-trial performance, current meta-analyses do not show meaningful benefits (Harnden et al. 2023).
Watermelon juice and L-citrulline can improve a vascular health marker called flow-mediated dilation in longer-term use, but translation to faster racing is inconsistent (Smeets et al. 2021).
Most studies test people when they’re fresh. We don’t yet know whether citrulline helps when you’re already fatigued late in a session or race.
I bloody love watermelon, and always feel pretty epic riding home from the grocery store with a massive one in my pannier bag. But, I’ve never tried a citrulline supplement or citrulline malate. Folks who have, tell me it has a sour taste, which means it might be your yin to the yang of a sweet sugary drink.
Typical research doses are about 3 grams of L-citrulline or about 8 grams of citrulline malate taken about 60 minutes before exercise. Some studies suggest that daily dosing for more than 7 days might matter more than a single hit, but results are mixed (Vårvik et al. 2021; Gonzalez et al. 2023).
Bottom line on mechanisms: the evidence for better muscle blood flow during exercise is mixed, and the role of added malate is still up in the air (Gough et al.2021; Aguiar et al.2022). Overall, the current body of evidence is small, the acute vs. chronic effects are not well defined, and the varying dose and duration among studies make firm conclusions difficult.
If you choose to use citrulline or watermelon juice, a reasonable dose is:
~3 grams of L-citrulline (or ~8 grams of citrulline malate) about 60 minutes before exercise is a reasonable starting point based on research use.
Daily dosing for more than 7 days might have a bigger effect than a single pre-exercise dose, but that’s not nailed down.
Matching the suggested dose with watermelon would mean roughly 7.5 to 105 KILOGRAMS of watermelon per day depending on variety and water content — not happening for most of us, but(fun to imagine. (Note: the citrulline content of watermelon ranges from 3.9 to 28.5 mg/g dry weight)
Taking more doesn’t necessarily mean a bigger effect.
Can citrulline and watermelon enhance athletic performance?
Taking citrulline or watermelon juice before a strength session is somewhat likely to improve performance.
The effect sizeAn effect size is a standardized measure of the magnitude of an effect of an intervention. Unlike p-values, effect sizes show how large the effect is and indicate how meaningful it might be. Common effect size measures include standardised mean difference (SMD), Cohen’s d, Hedges’ g, eta-squared, and correlation coefficients. is trivial to small.
Citrulline and watermelon juice are unlikely to improve endurance performance, but there is little research so effects are uncertain.
Due to insufficient research it is unclear how effects compare between trained athletes and untrained folks, and between males and females.
Keep in mind: because of there is only a small number of trials with a small number of participants, and because effects are inconsistent between studies, certaintyCertainty of evidence tells us how confident we are that the results reflect the true effect. It’s based on factors like study design, risk of bias, consistency, directness, and precision. High certainty means strong, consistent research. Low certainty means more doubt and less confidence, and that new studies could easily change the conclusions. (confidence) in the overall effect sizes reported in meta-analysesA meta-analysis quantifies the overall effect size of a treatment by compiling effect sizes from all known studies of that treatment. is low-to-moderate at best. Therefore, additional high-quality randomised controlled trialsThe “gold standard” approach for determining whether a treatment has a causal effect on an outcome of interest. In such a study, a sample of people representing the population of interest is randomised to receive the treatment or a no-treatment placebo (control), and the outcome of interest is measured before and after exposure to the treatment and control. are needed to increase the confidence in the currently reported effects.
To minimise the risk of consuming a supplement that contains prohibited substances, only choose products that have been independently tested (e.g., Informed Sport). And, remember: Supplements do not make athletes and do not replace training; they're just the icing on a very well-baked cake. Before reaching for pills and potions, optimise your training load and dial in your sleep, nutrition, and rest.
How to use this: If you want to try it, start with 3 grams of L-citrulline or about 8 grams of citrulline malate about 60 minutes before heavy lifting or hard intervals. Log how you feel and what you lift or output. If you notice zero change after 2 to 3 weeks of targeted use, save your cash and move on.
Strengthen the fight for clean sport
Remember: You are the only person responsible for what goes in your body! Ignorance is not an excuse! Stay educated. Be informed.
Consult WADA’s prohibited list, cross-check your meds against the Global DRO drug reference list, and only choose supplements that have been tested by an independent body (e.g., Informed Sport or LabDoor).
Information you can trust. All content on Veohtu is meticulously researched and written by Thomas Solomon, PhD. He does not sell supplements, recovery products, or ad space, and he has no sponsorships, brand affiliations, or ambassador roles. Everything you read reflects his independent views, shaped solely by peer-reviewed scientific evidence — and that will never change.
Full list of meta-analyses examining citrulline and watermelon for performance.
Here are the meta-analyses I've summarised above:
Effects of citrulline on endurance performance in young healthy adults: a systematic review and meta-analysis. Harnden et al. (2023) J Int Soc Sports Nutr
Effects of Citrulline Supplementation on Different Aerobic Exercise Outcomes: A Systematic Review and Meta-Analysis. Viribay et al. (2022) Nutrients
Effects of Citrulline Malate Supplementation on Muscle Strength in Resistance-Trained Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Aguiar et al. (2022) J Diet Suppl
Effect of food sources of nitrate, polyphenols, L-arginine and L-citrulline on endurance exercise performance: a systematic review and meta-analysis of randomised controlled trials. Noah M. A. d’Unienville, Henry T. Blake, Alison M. Coates, Alison M. Hill, Maximillian J. Nelson & Jonathan D. Buckley. J Int Soc Sports Nutr (2021)
Acute Effect of Citrulline Malate on Repetition Performance During Strength Training: A Systematic Review and Meta-Analysis. Vårvik FT, Bjørnsen T, Gonzalez AM. Int J Sport Nutr Exerc Metab (2021)
Nutritional Ergogenic Aids in Racquet Sports: A Systematic Review. Vicente-Salar N, Santos-Sánchez G, Roche E. Nutrients (2020)
Effects of Citrulline Supplementation on Exercise Performance in Humans: A Review of the Current Literature. Gonzalez AM, Trexler ET. J Strength Cond Res (2020)
Effect of citrulline on post-exercise rating of perceived exertion, muscle soreness, and blood lactate levels: A systematic review and meta-analysis. Rhim HC, Kim SJ, Park J, Jang KM. J Sport Health Sci (2020)
Effects of Citrulline alone or combined with exercise on muscle mass, muscle strength, and physical performance among older adults: a systematic review. Aubertin-Leheudre M, Buckinx F. Curr Opin Clin Nutr Metab Care (2020)
Acute Effects of Citrulline Supplementation on High-Intensity Strength and Power Performance: A Systematic Review and Meta-Analysis. Trexler ET, Persky AM, Ryan ED, Schwartz TA, Stoner L, Smith-Ryan AE. Sports Med (2019)
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Who is Thomas Solomon?
My knowledge has been honed following 20+ years of running, cycling, hiking, cross-country skiing, lifting, and climbing, 15+ years of academic research at world-leading universities and hospitals, and 10+ years advising and coaching in athletic performance and lifestyle change.
I have a BSc in Biochemistry, a PhD in Exercise Science, and over 90 peer-reviewed publications in medical journals.
I'm also an ACSM-certified Exercise Physiologist (ACSM-EP), an ACSM-certified Personal Trainer (ACSM-CPT), a VDOT-certified Distance Running Coach, and a UKVRN Registered Nutritionist (RNutr).
Since 2002, I’ve conducted biomedical research in exercise and nutrition and have taught and led university courses in exercise physiology, nutrition, biochemistry, and molecular medicine.
And, with my personal experience of competing on the track (800m to 10,000m), the road (5 k to marathon), on the trails, and in the mountains, by foot, bicycle, cross-country ski, and during obstacle course races (OCR), I deeply understand what it's like to train and compete — I've been there, done it, and gotten sweat, mud, and tears on my t-shirt.
Disclaimer: I occasionally mention brands and products, but it is important to know that I don't sell recovery products, supplements, or ad space, and I'm not affiliated with / sponsored by / an ambassador for / receiving advertisement royalties from any brands. I have conducted biomedical research for which I’ve received research money from publicly-funded national research councils and medical charities, and also from private companies, including Novo Nordisk Foundation, AstraZeneca, Amylin, the A.P. Møller Foundation, and the Augustinus Foundation. I’ve also consulted for Boost Treadmills and Gu Energy on R&D grant applications, and I provide research and scientific writing services for Examine.com. Some of my articles contain links to information provided by Examine.com but I do not receive any royalties or bonuses from those links. Importantly, none of the companies described above have had any control over the research design, data analysis, or publication outcomes of my work. I research and write my content using state-of-the-art, consensus, peer reviewed, and published scientific evidence combined with my empirical evidence observed in practice and feedback from athletes. My advice is, and always will be, based on my own views and opinions shaped by the scientific evidence available. The information I provide is not medical advice. Before making any changes to your habits of daily living based on any information I provide, always ensure it is safe for you to do so and consult your doctor if you are unsure.