What is citrulline?

L-citrulline is an amino acid involved in the urea cycle. Following ingestion, it can increase arginine availability, which contributes to the production of nitric oxide.

Nitric oxide participates in the regulation of blood vessel dilation. Citrulline is therefore frequently included in pre-workout products designed to support blood flow and the sensation of a muscular pump.

L-citrulline or citrulline malate?

L-citrulline provides the amino acid in its free form. Citrulline malate combines citrulline with malic acid. Products may use different ratios, including 1:1 and 2:1.

Consequently, two supplements containing the same total weight of citrulline malate may not provide the same amount of actual L-citrulline. A clearly disclosed ratio allows for a more accurate product comparison.

What does the research show?

Some studies report improvements in repetition performance, perceived exertion or post-exercise muscle soreness. A systematic review identified a potential reduction in perceived exertion and soreness following exercise.

Nevertheless, results are inconsistent. A meta-analysis found no clear improvement in muscular strength among healthy or resistance-trained adults, while findings relating to endurance performance remain limited and conflicting.

Citrulline should therefore not be described as a guaranteed method of increasing strength or muscle growth.

When is it used?

Citrulline is generally consumed before exercise. The relevant serving size depends on whether the product contains pure L-citrulline or citrulline malate and on the actual ratio of the blend.

When comparing products, the amount of pure citrulline per serving and the complete pre-workout formula should be considered.

Conclusion

L-citrulline and citrulline malate are popular ingredients for blood flow and training pump. Research suggests possible benefits for fatigue and selected performance outcomes, but the overall evidence remains mixed.

References

• Gonzalez AM, Trexler ET. Effects of Citrulline Supplementation on Exercise Performance in Humans: A Review of the Current Literature. Published: 2020.
• Aguiar AF et al. Effects of Citrulline Malate Supplementation on Muscle Strength in Resistance-Trained Adults: A Systematic Review and Meta-Analysis. Published: 2022.
• Rhim HC et al. Effect of Citrulline on Post-Exercise Rating of Perceived Exertion, Muscle Soreness and Blood Lactate Levels: A Systematic Review and Meta-Analysis. Published: 2020.