On a warm Saturday morning, a local running club hosted an unusual challenge: a friendly 5-mile race where participants could only rely on “foods that boost stamina.” One runner showed up holding a giant slice of watermelon. People laughed—until he won the race by a stunning margin. When someone asked for his secret, he simply said, “There’s power hidden in watermelon.”
At first, it sounded like a joke. But he wasn’t wrong. Watermelon is one of the richest natural sources of an amino acid called L-citrulline—now widely studied for its strong role in energy, exercise endurance, blood flow, and overall muscle performance. Years after that race, many athletes and active individuals are using L-citrulline supplementation as a reliable way to support workouts and daily vitality.
Today’s guide breaks down everything you need to know about L-citrulline, how it works inside the body, and why it has become one of the most trusted dietary supplements for exercise performance.
What Is L-Citrulline?
L-citrulline is a naturally occurring amino acid. Unlike some amino acids used to build muscle protein directly, citrulline plays a more indirect—but incredibly powerful—role in supporting blood vessels, energy production, endurance, and overall performance.
You can get citrulline from:
• watermelon
• some squash and gourds
• nuts
• legumes
• nutritional supplements
To understand why citrulline increases endurance and energy so effectively, you need to look at what it does once it enters the bloodstream.
How L-Citrulline Works in the Body
Instead of being used immediately like other amino acids, L-citrulline goes through a unique process:
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It is absorbed into the blood.
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The kidneys convert it into L-arginine.
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Arginine boosts nitric oxide (NO) production.
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Nitric oxide relaxes and widens blood vessels.
This chain reaction supports:
• better circulation
• improved oxygen delivery
• enhanced nutrient transport to muscles
• higher endurance during aerobic exercise
Interestingly, citrulline supplementation often increases arginine levels more effectively than taking arginine itself, because citrulline bypasses early digestion and is better utilized by the body.
This is why “citrulline and L-arginine” often appear together in research discussing nitric oxide synthase and blood flow.
L-Citrulline and Nitric Oxide: The Heart of Its Benefits
Nitric oxide is a signaling molecule essential for blood vessel function. When NO levels rise, blood vessels relax, circulation improves, and muscles receive more oxygen.
This is the primary reason L-citrulline is used to:
• support endurance
• improve energy
• assist muscle power
• enhance blood flow
Better circulation means your body works more efficiently during both aerobic exercise and strength training. Whether you're running, cycling, lifting weights, or doing high-intensity intervals, boosting nitric oxide can help you perform longer and recover more quickly.
Exercise Performance: Where Citrulline Really Shines
Research suggests citrulline increases endurance by supporting steady oxygen delivery and reducing the feeling of early fatigue. Because your muscles work more efficiently, you may notice:
• improved stamina
• faster bursts of effort
• reduced workout fatigue
• smoother heart rate during exercise
• better post-exercise recovery
People performing high-intensity workouts often use citrulline to support longer training sessions without losing energy halfway through.
Citrulline supplementation has also been studied for muscle pumps, with many users reporting a noticeable difference in muscle fullness and vascularity during workouts due to increased blood flow.
L-Citrulline and Blood Pressure
Nitric oxide doesn’t just help athletes. It also supports blood vessel relaxing function, which can help maintain healthy blood pressure levels.
Some studies show citrulline increases nitric oxide synthase activity, which may be beneficial for individuals with stiffened blood vessels or those seeking natural circulation support.
While it is not a treatment for medical conditions, its effects on vascular health have drawn interest from both wellness communities and researchers.
L-Citrulline, Arginine, and Erectile Function
Because blood flow affects multiple parts of the body, the benefits go beyond exercise.
Improving nitric oxide levels has long been associated with supporting erectile function. Citrulline supplementation may help promote natural circulation to areas dependent on strong blood flow. For those who prefer a nutritional approach, increasing arginine through citrulline offers a gentle, supportive option.
Again, supplements are not treatments, but citrulline’s circulatory benefits can have wide-ranging effects.
The Urea Cycle: An Overlooked Benefit
Citrulline is also part of the urea cycle—the process that helps the body safely remove ammonia, a waste product produced during exercise.
When ammonia builds up, muscles fatigue more quickly. Supporting the urea cycle through citrulline may help maintain endurance and reduce the “burnout” feeling during intense training.
This is especially valuable for athletes, distance runners, endurance cyclists, and anyone performing prolonged activities.
L-Citrulline vs. L-Arginine: Which Is Better?
Although both amino acids support nitric oxide, citrulline often comes out on top for several reasons:
• it is better absorbed
• it lasts longer in the body
• it increases arginine levels more effectively
• it bypasses digestion losses
• it supports both circulation and ammonia removal
For these reasons, citrulline supplementation remains a preferred choice for aerobic exercise and muscle support.
Muscle Support and Protein Synthesis
Even though citrulline doesn’t directly build muscle protein, it creates an environment where muscles perform better, recover faster, and receive better nutrient flow.
This can indirectly support:
• muscle growth
• muscle repair
• training consistency
• performance longevity
Some studies suggest citrulline’s effect on circulation may help amino acids reach muscles more efficiently, supporting recovery after exercise.
L-Citrulline and Cholesterol
Research on high cholesterol diets suggests that citrulline may help support vascular flexibility, nitric oxide function, and artery health. Again, citrulline is not a treatment for medical conditions, but its circulatory effects remain an area of ongoing study.
Possible Side Effects
Citrulline is well-tolerated for most people. Common reports are mild and rare, such as:
• stomach discomfort
• slight nausea
• temporary digestive changes
These usually occur with very high doses. Most people handle standard supplementation well, especially when taken with water before workouts.
As always, people with medical conditions or those taking medications should consult a healthcare professional before beginning any new supplement.
Choosing a Quality Citrulline Supplement
When selecting citrulline supplements, purity matters. Many prefer powders because they offer flexible dosing and fast absorption.
A high-quality option is this pure powder formula:
https://dailyvita.com/products/now-foods-l-citrulline-pure-powder-4-oz
Look for:
• pure L-citrulline
• no unnecessary fillers
• transparent sourcing
• reliable manufacturing standards
Consistency is key to experiencing benefits.
Supporting Your Performance Naturally
Whether you're an athlete looking to improve exercise performance or someone simply trying to maintain better energy and endurance during everyday activities, L-citrulline offers a supportive, natural approach.
Its unique ability to increase arginine, boost nitric oxide, and enhance circulation makes it a popular choice for those aiming to feel stronger, more energized, and more capable—both inside and outside the gym.
If you're looking for a supplement that supports stamina, circulation, and muscle performance, L-citrulline may be exactly the missing link your routines have been waiting for.