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Citrulline - The Superior NO Booster
What is Citrulline?
L-Citrulline is a non-essential amino acid naturally found in watermelons (hence the name – "Citrullus" is the botanical genus name for watermelon) and other cucurbits. In the human body, citrulline is an intermediate in the urea cycle and serves as an indirect precursor to arginine – the direct substrate for nitric oxide (NO) synthesis.
The Citrulline-Arginine-NO Cycle
Understanding why citrulline often works better than direct arginine requires insight into biochemistry:
Citrulline → (Kidneys) → Arginine → (NOS enzymes) → NO + Citrulline
When arginine is taken orally, a large portion is broken down in the gut and liver by the enzymes arginase and arginine deiminase before reaching systemic circulation (first-pass effect). Citrulline, on the other hand, is minimally broken down in the gut and efficiently reaches the kidneys, where it is converted to arginine. The result: Orally administered citrulline increases plasma arginine levels more effectively than equivalent doses of oral arginine.
Effects of NO on Muscle Performance
Nitric oxide (NO) is a gaseous signaling molecule with widespread effects:
- Vasodilation: NO relaxes the smooth muscle cells in blood vessel walls – they widen. More blood, more oxygen, more nutrients to the muscles
- Muscle "Pump": Increased blood flow = more pronounced vascularization and the characteristic "pump" feeling during training
- Mitochondrial Biogenesis: NO stimulates the formation of new mitochondria (long-term important for endurance performance)
- Reduced Ammonia Accumulation: NO improves urea cycle efficiency, which reduces muscle ammonia accumulation (a fatigue factor)
Citrulline vs. Citrulline Malate
| Form | Composition | Recommended Dose | Benefit |
|---|---|---|---|
| L-Citrulline | 100% Citrulline | 6–8 g | Pure NO Boost |
| Citrulline Malate 2:1 | 2 parts Citrulline, 1 part Malate | 8–10 g | NO Boost + Aerobic Energy |
The malate (malic acid) in citrulline malate serves as a substrate in the Krebs cycle and is intended to improve energy production. Studies using citrulline malate show slightly better performance than L-citrulline alone – possibly due to the additive malate effect.
Proven Effects through Studies
- Perez-Guisado & Jakeman (2010): 8 g Citrulline Malate before bench press → 52.9% more repetitions in the last set, 40% less muscle soreness 24h later
- Bailey et al. (2015): Citrulline increased VO₂max and improved endurance performance in cyclists
- Several meta-analyses confirm: Citrulline reduces muscle soreness and improves repetition performance in strength training
Dosage
| Form | Dose | Timing |
|---|---|---|
| L-Citrulline | 6–8 g | 30–60 min before training |
| Citrulline Malate (2:1) | 8–10 g | 30–60 min before training |
Frequently Asked Questions (FAQ)
Can I take Citrulline daily, even on rest days?
Yes. Daily citrulline intake has no known issues. On rest days, it has less performance relevance but supports regeneration through improved blood flow.
Citrulline or Arginine – what should I buy?
Citrulline is better in all aspects of NO boosting: higher bioavailability, stronger plasma arginine increase, better study evidence. Citrulline is the clear choice.
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