Researchers tested whether two popular supplements—L-arginine and citrulline malate—could help trained men perform better during different types of exercise. These supplements are heavily marketed to athletes because they’re supposed to improve blood flow and muscle power. In this carefully controlled study, 46 healthy men took either the supplements or a placebo before doing three different types of workouts: a short, intense power test; a CrossFit-style workout; and a cardiovascular endurance test. The results were surprising: the supplements didn’t significantly improve performance in most tests, though they did help athletes reach peak power slightly faster in one test. This suggests that taking these supplements once before exercise may not be worth the cost for most active people.

The Quick Take

  • What they studied: Whether taking L-arginine and citrulline malate supplements together could help trained men exercise better and longer
  • Who participated: 46 healthy, trained men with an average age of about 25 years who regularly exercise
  • Key finding: The supplements didn’t improve most exercise performance compared to placebo, except for reaching peak power slightly faster in one specific test
  • What it means for you: If you’re considering buying these popular supplements to boost your workouts, this research suggests they may not deliver the promised benefits when taken once before exercise. However, this was a single study with a relatively small group, so more research is needed before making final conclusions.

The Research Details

This was a randomized, double-blind, placebo-controlled trial, which is considered the gold standard for testing whether something actually works. Here’s what that means in plain language: The researchers randomly assigned 46 trained men to receive either the supplement combination or a fake pill (placebo) that looked identical. Neither the participants nor the researchers knew who got the real supplements until after the study ended, which prevents bias from affecting the results.

The men were divided into three groups based on the type of exercise they performed. One group did the Wingate Anaerobic Test, which measures explosive power and strength in short bursts. Another group completed a 20-minute CrossFit workout called ‘Cindy’ that involves repeated rounds of pull-ups, push-ups, and air squats to test muscular endurance and functional fitness. The third group did the Harvard Step Test, which measures how well your heart and lungs work during exercise and how quickly you recover afterward.

Each participant took a dose of L-arginine (0.15 grams per kilogram of body weight) and citrulline malate (0.1 grams per kilogram of body weight) about 30-60 minutes before their assigned workout. The researchers then measured their performance and compared the results between the supplement and placebo groups.

This study design is important because it helps answer a real question that many athletes ask: ‘Will these supplements actually help me perform better?’ By using a placebo control group, the researchers could determine whether any improvements came from the supplements themselves or from other factors like believing the supplements would help (the placebo effect). Testing three different types of exercise is also valuable because supplements might work differently depending on whether you’re doing short, intense bursts of power, longer endurance activities, or functional fitness movements.

This study has several strengths: it was published in Scientific Reports, a reputable peer-reviewed journal; it used a double-blind, placebo-controlled design, which is the most reliable way to test supplements; and it tested multiple types of exercise rather than just one. However, there are some limitations to consider. The sample size of 46 participants is relatively small, which means the results might not apply to everyone. The study only tested the supplements once before exercise, not over weeks or months of regular use. Additionally, the study only included healthy, trained men, so the results may not apply to women, beginners, or people with certain health conditions.

What the Results Show

The main finding was disappointing for supplement companies: taking L-arginine and citrulline malate together did not significantly improve performance in most of the tests. For the CrossFit workout and the cardiovascular endurance test, the supplement group performed essentially the same as the placebo group. This means that despite the marketing claims about improved blood flow and muscle power, these supplements didn’t help people do more pull-ups, push-ups, air squats, or recover better from exercise.

There was one exception: in the Wingate Anaerobic Test (the short, intense power test), participants who took the supplements reached their peak power output slightly faster than those taking placebo. However, this small improvement was the only measurable benefit found across all three exercise tests. The researchers noted that this single positive finding was modest and may not be practically meaningful for most athletes.

The lack of significant results was somewhat surprising because L-arginine and citrulline malate are both heavily marketed and widely used by athletes. The theory behind them makes sense: both supplements are supposed to increase nitric oxide in the body, which helps blood vessels relax and improves blood flow to muscles. Better blood flow should theoretically deliver more oxygen and nutrients to working muscles, potentially improving performance. However, the theory didn’t translate into real-world performance improvements in this study.

While the study didn’t find major performance improvements, the researchers did measure various other outcomes during the exercises. These secondary measurements included peak power output, average power, total work performed, and recovery metrics. None of these showed significant differences between the supplement and placebo groups, except for the faster time to peak power mentioned above. This consistency across multiple measurements suggests that the lack of benefit wasn’t due to measuring the wrong things—the supplements simply didn’t provide the expected boost.

This study adds to a growing body of research suggesting that many popular supplements don’t work as well as their marketing claims suggest. Previous research on L-arginine and citrulline malate has shown mixed results, with some studies finding small benefits and others finding none. This new research leans toward the ’no benefit’ side of the debate, particularly for acute supplementation (taking it once before exercise). Some earlier studies that found benefits often used different dosages, tested chronic supplementation (taking it regularly over time), or studied different populations. The current study’s findings suggest that the specific dosage and timing used here—taking the supplements once before exercise—may not be effective, even though other approaches might be worth investigating.

Several important limitations should be considered when interpreting these results. First, the study only tested acute supplementation, meaning participants took the supplements just once before exercise. It’s possible that taking these supplements regularly over weeks or months might produce different results, though the study didn’t test this. Second, the sample size of 46 men is relatively small, which means the study might have missed real but small benefits that would only show up in a larger group. Third, all participants were healthy, trained men in their mid-20s, so these results may not apply to women, older adults, beginners, or people with certain health conditions. Fourth, the specific dosages used (0.15 g/kg of L-arginine and 0.1 g/kg of citrulline malate) may not be optimal—higher or lower doses might produce different results. Finally, the study didn’t measure blood levels of nitric oxide or other biochemical markers, so we don’t know whether the supplements actually did what they were supposed to do at the cellular level, even if they didn’t improve performance.

The Bottom Line

Based on this research, taking L-arginine and citrulline malate supplements once before exercise is not recommended as a reliable way to improve athletic performance in trained individuals (confidence level: moderate). The evidence suggests these supplements are unlikely to provide meaningful benefits for most people doing aerobic exercise, anaerobic exercise, or CrossFit-style workouts. However, this conclusion is based on a single study with a relatively small sample size, so it’s not definitive. If you’re currently taking these supplements, you might consider stopping to save money, unless you have other reasons for taking them. If you’re thinking about starting them, this research suggests you should probably invest your money elsewhere or wait for more convincing evidence.

This research is most relevant to trained athletes and fitness enthusiasts who are considering spending money on L-arginine and citrulline malate supplements. It’s particularly relevant if you’re looking for a quick performance boost before workouts. The findings are less relevant to people who are taking these supplements for other health reasons (like cardiovascular health) rather than athletic performance. The study only included men, so women should be cautious about applying these results to themselves, as supplements can affect men and women differently. People who are new to exercise, have certain health conditions, or take medications should consult with a doctor before taking any supplements.

If these supplements were going to work, you would likely notice improvements within a few workouts, since the study tested acute effects (taking them once before exercise). The fact that no significant improvements were seen suggests that waiting longer won’t help—if they don’t work in the short term, they’re unlikely to suddenly start working. However, it’s theoretically possible that taking these supplements regularly over weeks or months might produce different results, though this study didn’t test that approach.

Want to Apply This Research?

  • If users want to test whether these supplements work for them personally, they could track specific metrics like maximum weight lifted, number of repetitions completed, or workout duration before and after supplementation over 2-4 weeks. This would help them see if their individual response differs from the study results.
  • Rather than spending money on these supplements, users could redirect that investment toward evidence-based performance improvements like better sleep, proper nutrition, consistent training, and adequate hydration. The app could help track these factors and show users how they correlate with performance improvements.
  • Users interested in supplements should log their supplement use and performance metrics in the app to track their personal response over time. They could set reminders to record workout performance weekly and compare trends over months to see if any supplements actually help them individually, rather than relying solely on marketing claims or general research.

This research summary is for educational purposes only and should not be considered medical advice. The study tested acute supplementation in healthy, trained men and may not apply to all populations, including women, older adults, beginners, or people with health conditions. Before starting any new supplement, especially if you take medications or have existing health conditions, consult with a healthcare provider or registered dietitian. Individual responses to supplements can vary, and what doesn’t work for the group in this study might work differently for you. Always purchase supplements from reputable sources and look for third-party testing to ensure quality and safety.