Compared to some pre-workout ingredients (such as previous entries in this series, caffeine and beta-alanine), citrulline is a relative newcomer. However, the reason for including citrulline in a pre-workout is something these products have been chasing since the dawn of their existence: the pump! In this article, I’ll discuss whether citrulline is the king of pump-inducing ingredients, what that means for workout and sports performance, what the research shows regarding its efficacy, and how to take and dose it properly. So let’s dive in!
What Is Citrulline?
Citrulline is a non-essential amino acid, which means the body can produce it naturally. It is also found in some foods, such as watermelon. Unlike some amino acids that have a direct role in muscle, citrulline’s benefits for exercise performance stem from its role in the production of nitric oxide (NO) and its influence on blood flow and nutrient delivery to muscles.
How Citrulline Works
Citrulline has gained attention in recent years because of its ability to increase nitric oxide (NO) production. Importantly, it does so more effectively than other ingredients commonly found in pre-workouts, such as arginine (Ojeda et al., 2019). NO is a vasodilator, meaning it relaxes the inner muscles of the blood vessels, causing them to widen and increase blood flow. In other words, the pump!
However, this improved blood flow isn’t just for making your arms look bigger. In theory, it allows for better oxygen and nutrient delivery to muscles during exercise. More oxygen and nutrients (such as carbohydrates) getting to the muscle may enhance performance by delaying the onset of muscular fatigue and enabling you to go harder for longer.
What Can You Expect from Citrulline?
If there is a word to describe the research findings on citrulline’s efficacy it would be: inconsistent. We have some research showing moderate, but potentially meaningful, performance improvements and some showing little to no improvement. Here is a breakdown of citrulline’s effects on various aspects of fitness and performance:
Strength and Muscle Growth:
The most direct evidence of citrulline’s performance-enhancing capabilities is on repetition performance during strength training. Some studies report modest improvements in the number of repetitions athletes can perform before reaching failure (ranging from 6-16%). This may indirectly support muscle growth by allowing for greater training volume. However, direct evidence linking citrulline supplementation to increased muscle mass is sparse, and more research is needed to fully understand if these moderate increases rep performance actually lead to more muscle.
When it comes to outright increases in maximal strength, the effects of citrulline supplementation are unclear. Research has not consistently shown significant improvements in one-repetition maximum (1RM) tests. Like muscle growth, increased training volume may lead to strength gains, but we have very little research that directly measures strength (Trexler et al., 2019; Aguiar & Casonatto, 2021; Vavrik et al., 2021).
High-Intensity Exercise:
Some studies have shown improvements in sprint performance, with athletes able to maintain higher performance levels across multiple sprints. The specific magnitude of improvement can vary, with reports of around a 1.5% to 3% increase in performance in repeated sprint tests or short-duration high-intensity exercises. In activities like cycling sprints or all-out rowing tests lasting around 30 seconds to a minute, improvements in the total work completed or power output during the protocols have been seen, ranging from 1% to 6% (Gough et al., 2021; Nyawose et al., 2022).
Endurance:
Of all the performance outcomes, citrulline seems to have the least impact on aerobic endurance (i.e. activities lasting longer than 5 minutes). While citrulline may lower perceived exertion (how hard something feels), it has failed to show significant performance improvements consistently (Viribay et al., 2022; Harnden et al., 2023).
How and What To Take
In research showing performance improvements, doses of 6-8 grams of citrulline taken approximately 60 minutes before exercise appear to be most effective. Sometimes you will see citrulline malate on the label of a product. This is simply a mixture of citrulline and another compound called malate, which has a role in energy production. However, there’s no evidence that malate improves performance in humans and it lowers the amount of citrulline you get in each serving. I would suggest looking for just citrulline on the label.
Final Notes
Citrulline presents an intriguing option for athletes and fitness enthusiasts looking to get the most out of their training and performance. However, it’s clear that more research is needed to get a more concrete picture of its potential benefits and optimal usage protocols.
For now, if the bulk of your workouts are resistance training with higher rep ranges and getting a few extra reps per set is important to you and may get you closer to your goals, then citrulline might be worth considering. It may also be worth considering if you’re an athlete who must perform repeated high-intensity efforts (e.g. sprinting, jumping) over an extended period of time with insufficient rest between efforts. However, if you’re strength training with lower rep ranges or you’re a pure endurance athlete, it’s unlikely that citrulline will benefit you in a meaningful way.
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