Citrulline

Citrulline can be found in:

Starman PRO

Norateen Nitro

Possessed II

Vasculator

Vasculator Extreme

L-Citrulline: the science of more reps, more volume and a bigger pump

L-Citrulline (formula C6H13N3O3, molecular weight 175.2) is a non-essential amino acid best known as the ingredient behind "the pump." It is frequently supplied as citrulline malate, which pairs it with malic acid. It is one of the most reliably effective pre-workout ingredients in sports nutrition.

Mechanism of action: the arginine paradox

Nitric oxide (NO) is the molecule that widens blood vessels and drives blood flow to working muscle — and the body makes it from the amino acid arginine. The problem is that oral arginine is largely broken down in the liver before it reaches the bloodstream. L-Citrulline solves this: it bypasses liver first-pass metabolism, is converted to arginine in the kidneys, and therefore raises plasma arginine levels more effectively than arginine itself does (Schwedhelm et al., 2008).
More arginine means more nitric oxide, which means vasodilation, greater blood flow and improved delivery of oxygen and nutrients to the muscles you are training — plus faster clearance of ammonia and metabolic by-products through the urea cycle. The practical effect is that you fatigue later and complete more work.
The pathway can be summarised as: L-citrulline → ↑ plasma arginine → ↑ nitric oxide → vasodilation and blood flow → less fatigue and more reps per session.
1. Muscle building
Citrulline supports muscle growth indirectly but powerfully: by increasing the number of quality repetitions you complete, it increases total training volume — one of the primary drivers of hypertrophy. A systematic review and meta-analysis concluded that citrulline malate supplementation may meaningfully increase training volume by enhancing muscular endurance during high-intensity performance (Vårvik et al., 2021). More volume, session after session, is more accumulated stimulus for muscle growth.
2. Strength
In the landmark double-blind, placebo-controlled crossover trial, 41 men performed 16 sets of bench press at 80% of their one-rep max after taking either 8 g of citrulline malate or placebo. The citrulline group completed 52.9% more repetitions in the final set, with the advantage growing progressively across sets (Pérez-Guisado & Jakeman, 2010). Later work confirmed the effect in resistance-trained women, where lower-body repetitions rose by roughly 21%.
3. Power
Citrulline's benefit to high-intensity output comes from delayed fatigue. A systematic review and meta-analysis found citrulline supplementation significantly reduced ratings of perceived exertion after exercise, with a large effect size, alongside reduced muscle soreness (Rhim et al., 2020). A comprehensive review of the literature likewise reported beneficial effects across a range of strength and power measurements (Gonzalez & Trexler, 2020).
4. Stamina

For endurance, seven days of L-citrulline supplementation was shown to improve oxygen uptake kinetics and increase tolerance to high-intensity exercise in healthy adults — meaning the body reaches its working oxygen supply faster and sustains hard efforts longer (Bailey et al., 2015). Meta-analysis also supports improved aerobic endurance (Rhim et al., 2020).

Recovery: 40% less soreness

In the same landmark trial, citrulline malate produced a 40% reduction in muscle soreness at both 24 and 48 hours post-training, with over 90% of participants reporting a measurable decrease (Pérez-Guisado & Jakeman, 2010) — likely reflecting improved blood flow and faster ammonia clearance.

Key facts at a glance

• What it is: L-citrulline, a nitric-oxide precursor amino acid, C6H13N3O3; often supplied as citrulline malate.

• Mechanism: bypasses the liver to raise plasma arginine and nitric oxide better than arginine itself. • Muscle: increases training volume, a primary driver of hypertrophy (Vårvik 2021).

• Strength: 52.9% more repetitions in the final set at 80% 1RM vs placebo (Pérez-Guisado 2010).

• Power: significantly lower perceived exertion and delayed fatigue (Rhim 2020).

• Stamina: improved O2 uptake kinetics and high-intensity exercise tolerance (Bailey 2015).

• Recovery: 40% less muscle soreness at 24 and 48 hours.

• Dose used in trials: 6–8 g citrulline malate, taken 30–60 minutes pre-workout.

Full scientific references

• Pérez-Guisado J, Jakeman PM. Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness. Journal of Strength and Conditioning Research. 2010;24(5):1215–1222.

• Vårvik FT, Bjørnsen T, Gonzalez AM. Acute effect of citrulline malate on repetition performance during strength training: a systematic review and meta-analysis. International Journal of Sport Nutrition and Exercise Metabolism. 2021;31(4):350–358.

• Gonzalez AM, Trexler ET. Effects of citrulline supplementation on exercise performance in humans: a review of the current literature. Journal of Strength and Conditioning Research. 2020;34(5):1480–1495.

• Rhim HC, Kim SJ, Park J, Jang KM. Effect of citrulline on post-exercise rating of perceived exertion, muscle soreness, and blood lactate levels: a systematic review and meta-analysis. Journal of Sport and Health Science. 2020;9(6):553–561.

• Bailey SJ, Blackwell JR, Lord T, Vanhatalo A, Winyard PG, Jones AM. L-citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans. Journal of Applied Physiology. 2015;119(4):385–395.

• Schwedhelm E, Maas R, Freese R, et al. Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism. British Journal of Clinical Pharmacology. 2008;65(1):51–59.

Citrulline supports muscle growth indirectly, by increasing the training volume that drives hypertrophy. This information is educational and describes the ingredient's physiology and the findings of published research; it is not a therapeutic or medical claim. Individual results vary.