Best Oxygen Delivery Supplements for Endurance Athletes

Last updated: April 22, 2026

Key Takeaways: Oxygen Delivery Supplements That Actually Move the Needle

• L-Citrulline can top many oxygen delivery supplements by converting to arginine in the kidneys for sustained nitric oxide production and about 12% longer time-to-exhaustion in cyclists.¹
• Beetroot nitrates support natural vasodilation through a separate pathway but show variable results because effectiveness depends on individual oral bacteria.¹
• Nitrosigine raises arginine levels within minutes, which suits athletes who want a fast endurance boost that can last up to 6 hours.¹
• Cordyceps and CoQ10 support mitochondrial oxygen use, while iron underpins hemoglobin-based oxygen transport when blood work shows a need.¹
• For clinically aligned L-Citrulline dosing, explore Bucked Up’s pure L-Citrulline and related formulas to support your endurance goals.¹

Evidence-Backed Oxygen Delivery Supplements Ranked

1. L-Citrulline: Consistent Nitric Oxide Support for Endurance

How It Works: L-Citrulline follows a metabolic route that often outperforms direct arginine intake. Unlike L-arginine, which breaks down quickly in the gut and liver, L-citrulline is better absorbed and more effectively raises arginine levels. The amino acid travels to the kidneys, where argininosuccinate synthase and lyase enzymes convert it to L-arginine. This process supplies a steady stream of substrate for nitric oxide production.

Endurance Benefits: Research links L-citrulline to meaningful performance gains.¹ Cyclists taking L-citrulline cycled about 12% longer before exhaustion and produced more power during sessions.¹ In a 2010 randomized controlled trial of 41 men, 8 grams of citrulline malate increased repetitions by 53% in the second half of resistance workouts and reduced muscle soreness by 40% at 24–48 hours post-exercise.¹ These findings support both endurance and recovery benefits.¹

Optimal Dosing: Optimal doses of L-citrulline have not been set for any condition. Many athletes look at real-world formulations for guidance. Bucked Up pre-workout and Woke AF each deliver 6,000 mg of Citrulline Malate, while Mother Bucker provides 4,000 mg of pure L-Citrulline with Nitrosigine and AstraGin for absorption support.¹

2. Beetroot Nitrates: Plant-Based Nitric Oxide Support

How It Works: Beetroot juice, rich in dietary nitrates, converts in the body to nitric oxide, which relaxes blood vessels and supports oxygen delivery to muscles. This nitrate-to-nitric oxide route functions independently from the arginine-based nitric oxide system. It offers a plant-based option for athletes who prefer food-derived support.

Endurance Benefits: Dietary nitrate supplements show promising but variable evidence for improving endurance performance, especially in recreational athletes.¹ Outcomes depend heavily on nitrate-reducing bacteria in the mouth and gut. Two athletes can take the same dose and see very different responses.

Optimal Dosing: Consume beetroot juice 2–3 hours before exercise or use supplements with standardized nitrate content. The minimal effective dose often requires at least 5 mmol nitrate per 500 ml serving of beetroot juice, and only a few products consistently provide this amount.

3. Nitrosigine: Fast-Acting Arginine Support

How It Works: Nitrosigine, or inositol-stabilized arginine silicate, delivers arginine in a form that resists rapid breakdown. Clinical studies show that 1.5 grams of Nitrosigine can provide vasodilation comparable to 8 grams of citrulline malate.¹ This efficiency appeals to athletes who prefer smaller serving sizes.

Endurance Benefits: Nitrosigine starts working within minutes of consumption, which supports acute performance enhancement, and it maintains elevated arginine levels for up to 6 hours.¹ This window can cover both warm-up and main training blocks.

Optimal Dosing: Effective doses typically range from 1.5–3 grams taken 15–30 minutes before exercise. Bucked Up’s Mother Bucker combines Nitrosigine with pure L-Citrulline, creating a stack that targets both rapid and sustained nitric oxide support.

4. L-Arginine: Direct Nitric Oxide Precursor

How It Works: L-Arginine acts as the direct substrate for nitric oxide synthase enzymes. However, only about 30% of L-arginine reaches peripheral circulation after roughly 60% gastrointestinal processing and 15% liver metabolism. This first-pass effect limits how much of each dose supports nitric oxide production.

Endurance Benefits: In elderly cyclists, L-arginine combined with antioxidants increased anaerobic threshold by 16.7% after one week and raised power output by 22.51 watts.¹ These results suggest targeted benefits in specific populations.

Optimal Dosing: A 2011 meta-analysis reported that L-arginine supplementation reduced systolic blood pressure by 5.39 mmHg. Gastrointestinal side effects at higher doses can limit how much athletes comfortably use.

5. Cordyceps: Cellular Oxygen Use Support

How It Works: Cordyceps mushrooms contain compounds that may enhance mitochondrial ATP production and oxygen utilization efficiency at the cellular level. This mechanism focuses more on how cells use oxygen than on blood flow alone.

Endurance Benefits: Traditional use and early research suggest improvements in oxygen uptake and exercise capacity, although evidence remains more limited than for primary nitric oxide boosters.¹ Athletes often treat Cordyceps as a secondary add-on rather than a standalone solution.

Optimal Dosing: Typical doses range from 1–3 grams daily of standardized Cordyceps extract. Consistent daily use appears more common than single pre-workout servings.

6. Coenzyme Q10: Mitochondrial Energy Chain Support

How It Works: CoQ10 depletion disrupts electron transfer in the inner mitochondrial membrane by impairing shuttling of electrons between complexes I, II, and III, which are critical steps for ATP synthesis. Adequate CoQ10 helps maintain efficient energy production.

Endurance Benefits: A 2022 meta-analysis of 13 randomized controlled trials found that CoQ10 supplementation produced statistically significant reductions in fatigue scores versus placebo.¹ Daily doses of 100–200 mg appear particularly effective for people over 40, when natural CoQ10 levels often decline.

Optimal Dosing: Most protocols use 100–200 mg daily, especially in adults over 40. Taking CoQ10 with a meal that contains fat can support absorption.

7. Iron: Hemoglobin-Based Oxygen Transport

How It Works: Iron forms a key part of hemoglobin in red blood cells, enabling oxygen delivery to tissues and muscles, with each hemoglobin molecule carrying four oxygen molecules. Adequate iron status supports the basic capacity to move oxygen through the bloodstream.

Endurance Benefits: A double-blind randomized controlled trial in healthy non-anemic athletes found that iron supplementation significantly improved mood disturbance and perceived fatigue, with the strongest effects in female athletes.¹ These changes can influence training quality and consistency.

Optimal Dosing: Many women use 18–25 mg daily, while the recommended amount of iron for adult men 19–50 years is 8 mg daily. Pairing iron with vitamin C can enhance absorption. Supplementation works best when blood work confirms deficiency or low stores.

L-Citrulline, Arginine, and Beetroot: What the Data Comparison Shows

Supplement	Mechanism	Absorption/Bioavailability	Endurance Outcomes
L-Citrulline	Renal conversion to arginine	Nearly 100% plasma absorption	12% longer time-to-exhaustion
L-Arginine	Direct nitric oxide precursor	30% reaches circulation	16.7% anaerobic threshold increase
Beetroot	Nitrate-to-nitric oxide conversion	Variable (depends on oral bacteria)	Promising but variable results

This comparison highlights why L-Citrulline often stands out. Its near-complete plasma absorption and consistent 12% improvement in time-to-exhaustion contrast with arginine’s lower bioavailability and beetroot’s person-to-person variability.¹

L-Citrulline for Oxygen Use: Smart Stacking and Safety

L-Citrulline supplementation improves O2 uptake kinetics during exercise, which supports more efficient oxygen delivery to working muscles.¹ Bailey et al. (2015) reported that L-citrulline improved O2 uptake kinetics, reduced blood pressure, and enhanced high-intensity exercise performance.¹ These effects align with athletes’ goals of delaying fatigue and sustaining pace.

Many athletes increase L-Citrulline effectiveness through targeted stacking. A 6,000 mg Citrulline Malate serving with AstraGin may support absorption while keeping intake below the 10 gram range where gastrointestinal discomfort becomes more common.¹ Individuals with cardiovascular conditions, low blood pressure, or those using blood pressure medications should consult healthcare providers because of potential interactions. This step helps match dosing to personal health status.

Bucked Up features science-backed citrulline dosing in both Citrulline Malate and pure L-Citrulline formats, giving you options to match your training style and tolerance.

Frequently Asked Questions About Oxygen Delivery Supplements

Which supplement suits runners versus cyclists?

L-Citrulline supports both running and cycling by improving oxygen delivery and reducing ammonia buildup. The roughly 12% improvement in time-to-exhaustion seen in cycling research can translate to better pacing and stronger finishes in running, since both sports rely on sustained oxygen use and fatigue resistance.¹

How does L-Citrulline compare to beetroot for endurance?

L-Citrulline generally provides more predictable results than beetroot nitrates. Beetroot engages a separate nitric oxide pathway, yet its impact varies widely based on oral bacteria and nitrate-reducing capacity. L-Citrulline’s kidney conversion mechanism raises arginine reliably across a broader range of individuals.

When should I take oxygen delivery supplements?

L-Citrulline and citrulline malate work best when taken 60–90 minutes before exercise to align with peak plasma arginine levels. Beetroot juice usually needs 2–3 hours for nitrate conversion, while Nitrosigine often takes effect within 15–30 minutes. Consistent daily use can support a higher baseline for nitric oxide production.

Are oxygen delivery supplements safe for daily use?

L-Citrulline shows a strong safety profile at 3–6 grams daily. Studies report no serious adverse events with doses up to 15 grams in healthy adults.¹ People on blood pressure medications should watch for additive effects, and those with kidney disorders should work with a healthcare professional before using higher doses.

What are the potential downsides of nitric oxide boosters?

Very high single doses above 10 grams can cause mild gastrointestinal discomfort in some users.¹ A few people experience headaches from vasodilation. Exceeding recommended amounts may saturate arginine pathways without adding benefits. Gradual introduction and appropriate dosing help reduce these issues.

Conclusion: Using L-Citrulline and Bucked Up to Extend Endurance

Among oxygen delivery supplements available to endurance athletes in 2026, L-Citrulline stands out as a well-studied option. Its kidney-based conversion pathway, high bioavailability, and consistent performance data make it a practical choice for athletes who want to push past plateaus and extend time-to-exhaustion.¹

Bucked Up’s transparent labeling and citrulline-focused formulas give you clear dosing choices. Their Bucked Up and Woke AF pre-workouts each supply 6,000 mg of Citrulline Malate, while Mother Bucker offers 4,000 mg of pure L-Citrulline paired with Nitrosigine and AstraGin. These combinations allow you to tailor nitric oxide support to your training intensity and recovery needs.

If you want to test L-Citrulline’s documented endurance benefits for yourself, start with Bucked Up’s citrulline lineup and track changes in time-to-exhaustion and workout quality.

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