Nitric Oxide - Pump or Frump?

The Quick Take

Nitric oxide "pump" supplements work by dilating your blood vessels, pushing more blood, oxygen, and nutrients to your working muscles. The most evidence-backed options are L-citrulline (3–6 g) or citrulline malate (6–8 g at 2:1 ratio) taken about 45–60 minutes before training, and dietary nitrate like beetroot juice (providing around 6–8 mmol nitrate) taken 2–3 hours pre-workout.

Skip arginine by itself—it's largely inferior to citrulline. Those fancy salts like AAKG and agmatine? The data's pretty weak. Expect small, context-dependent performance gains that work best for high-rep sets and endurance time trials, plus that satisfying pump feeling.

What Exactly Is Nitric Oxide?

Nitric oxide (NO) is a gaseous signalling molecule your body makes from L-arginine using an enzyme called endothelial NO synthase (eNOS). Here's the simple chain reaction: more NO leads to vasodilation (wider blood vessels), which increases blood flow, potentially improving muscle oxygenation, that coveted "pump," and how hard the work feels.

How Does It Actually Work?

Think of nitric oxide as your gym's traffic warden—it tells your blood vessels to open up the lanes. Wider lanes mean your set feels a bit smoother and recovery between sets happens a little quicker.

You can boost NO through two main routes:

Supply precursors: Give your body L-citrulline, which converts to arginine, which then converts to NO.

Provide dietary nitrate: Eat nitrate-rich foods like beetroot or spinach. Bacteria in your mouth convert the nitrate to nitrite, which then becomes NO (this is called the nitrate–nitrite–NO pathway).

What Does the Science Say?

Strong and Consistent Evidence

L-citrulline and citrulline malate: These improve blood arginine levels better than taking arginine directly. Studies show modest increases in reps to failure, reduced muscle soreness the next day, and improved perceived effort during resistance training at typical doses.

Dietary nitrate (beetroot): Multiple studies show improvements in time-trial performance, work economy, and high-intensity intermittent endurance—especially in less-trained to moderately trained athletes.

Promising but Mixed Results

Nitrosigine® (inositol-stabilized arginine silicate at 1.5 g): Good data on raising arginine levels and early studies showing benefits for blood vessel function and pump. Performance data is growing but not universal yet.

Glycerol plus NO stacks: Can increase total body water and enhance that pump feeling, but performance effects are inconsistent.

Limited or Weak Evidence

Oral arginine (standard or AAKG): Doesn't raise blood arginine levels well because your gut and liver break it down. Performance benefits are largely underwhelming compared to citrulline.

Agmatine, beet powders with unknown nitrate content, generic "NO blends": Evidence is either scarce or the products are under-dosed.

Is Nitric Oxide Supplementation Right for You?

Great Fit If You're:

• A lifter chasing better pumps and that one-more-rep effect on higher-rep sets

• Involved in team sports or HIIT training

• A cyclist or runner doing time trials or repeated sprints

Lower Priority If You're:

• Focused on max-strength work with 1–3 rep sets (effects are minimal here)

• Already a highly trained endurance elite (you'll see smaller improvements from nitrate)

• Perfectly satisfied with a coffee-only pre-workout routine

What Results Can You Expect?

For resistance training: A small but meaningful bump in reps to failure (especially in the 8–15 rep range), slightly less muscle soreness the next day, and a better pump with improved perceived effort.

For endurance: Nitrate can improve time-trial completion times and reduce the oxygen cost of submaximal work by about 1–3%—which can be the difference-maker in competition.

Timeline: Citrulline works within about 60 minutes. Nitrate needs 2–3 hours, and consistent intake tends to work best.

Dosage and Forms

L-Citrulline / Citrulline Malate

L-citrulline: 3–6 g taken about 45–60 minutes pre-workout.

Citrulline malate (2:1 ratio): 6–8 g pre-workout (this gives you roughly 4–5.3 g of actual citrulline).

You can split doses if it helps with digestive comfort. Works well combined with 200 mg caffeine and 2–3 g beta-alanine (if you're already using beta-alanine).

Dietary Nitrate (Beetroot, Spinach, Arugula)

Target nitrate amount: About 6–8 mmol (roughly 370–500 mg) taken 2–3 hours before your event or workout.

Important note: Mouthwash can interfere with the nitrate to nitrite conversion, so avoid antibacterial mouthwash around dosing time.

Forms to use:

• About 500 ml of beetroot juice

• Concentrated beetroot "shots" standardized for nitrate content

• Capsules or powders—but only if the nitrate content is clearly declared

Other Options

Nitrosigine®: 1.5 g taken 30–60 minutes pre-workout. Shows decent arginine elevations with early performance and pump data.

Arginine: You'd typically need 6–10 g to see any effect, but it causes more digestive issues and has weaker effects compared to citrulline—not the preferred choice.

Glycerol: 1–2 g (or 0.5–1 g per kg body weight for older protocols) may help with pump and hydration. Watch out for clumping and potential digestive upset.

Safety and Side Effects

Citrulline: Generally very well tolerated. You might experience occasional mild digestive discomfort.

Nitrate: Usually safe from foods and standardized shots. It may lower blood pressure, so use caution if you have low blood pressure or take antihypertensive medications or PDE-5 inhibitors like sildenafil (Viagra). Beetroot can cause beeturia—pink urine or stool that's completely harmless.

Arginine: More likely to cause digestive distress like bloating or diarrhoea at effective doses.

Stacking with caffeine: Generally fine, but avoid combining very high stimulant doses with large vasodilator stacks if you're sensitive to blood pressure changes.

What to Look for When Buying

✓ Transparent dosing: Look for clear labels like "L-citrulline 3–6 g" or "citrulline malate 6–8 g (2:1)"—not vague "NO blend 1,000 mg"

✓ Standardized nitrate content: Should state mg of nitrate per serving, not just "beet powder"

✓ Minimal fluff: Skip products heavy on AAKG or agmatine unless they're well-dosed with supporting data

✓ Third-party testing: Look for Informed Choice or NSF certification if you compete in tested sports

✓ Taste considerations: High-dose citrulline malate is tart; nitrate shots can taste earthy—test your tolerance before race day

The Final Word

For real-world gym use, citrulline (3–6 g) or citrulline malate (6–8 g) taken about an hour before your workout is the most reliable, low-side-effect route to better pumps and a few extra reps. For endurance work and time trials, nitrate from standardized beetroot shots taken 2–3 hours beforehand can shave precious seconds off your time.

Arginine by itself and exotic "NO blends" rarely outperform these basics. Keep your expectations realistic: these supplements are useful, not magical.

References

Research supporting this guide includes systematic reviews and randomized controlled trials on L-citrulline and citrulline malate for resistance performance and delayed onset muscle soreness; randomized trials and meta-analyses on dietary nitrate (beetroot juice) for endurance time-trial performance and exercise economy; pharmacokinetic comparison studies of citrulline versus arginine (plasma arginine levels and NO surrogates); and emerging data on inositol-stabilized arginine silicate (Nitrosigine®) for endothelial function and pump outcomes.