CO2 Tolerance

Clear the Oxygen Traffic Jam

Why can some people run for miles without tiring, while others gasp for air after just a few steps? It's not just fitness — it's all about CO2 tolerance. Learn how it really works.

Learn More Take the Test

What is CO2 Tolerance?

CO2 tolerance is your "breathing fitness level" - how well your body adapts to rising CO2 levels during exercise or breathwork. Just like some people can run longer than others, some can handle higher CO2 with ease and comfort.

You can train it, like any other skill.

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Test Your CO2 Tolerance

Choose your testing method

Quick check: Hold your breath right now. If you need to stop the breath-hold within 30 seconds, you have low tolerance. If you can stay calm for 100+ seconds, you have high tolerance.

With more detailed instructions

Responsive testing exercise in the app

Why It Matters

How does CO2 tolerance affect your daily life and well-being?

❌ Low CO2 Tolerance

  • Easily out of breath
  • High stress levels
  • Poor fitness level
  • Poor sleep quality
  • Often fatigued
  • Low oxygen consumption

✅ High CO2 Tolerance

  • Effortless breathing always
  • Calm under pressure
  • High fitness level
  • Deep restful sleep
  • Always energized
  • High oxygen consumption

About Ed Reuvers

Drs. Ed Reuvers has over 25 years of experience in breathing practices, initially as a Buddhist monk and later as a breathing instructor.

Through many years of helping students improve their CO2 tolerance, Ed noticed that students often struggle to find the right practice intensity and measure their CO2 tolerance accurately. This inspired him to develop a new program with responsive in-app guidance that monitors your performance and adjusts automatically.

Program Creator
CO2 Tolerance Expert
25+ Years Experience
Economics Graduate
Drs. Ed Reuvers, founder of the CO₂ tolerance program
Drs. Ed Reuvers as a young Buddhist monk

Reuvers® Breathing Program

Solid Foundations

Built upon Buteyko, Pranayama, and Fire Breathing traditions

Advanced Sensing

Precisely measures CO2 tolerance without extra sensor devices.

Auto Adjustment

Adapts exercise intensity automatically for better relaxation

Golden Zone

Keeps you practicing at the right intensity level for optimal results

Ready to Start?

The 30-day Reuvers® program builds on traditional breathing techniques to intelligently sense your CO2 tolerance and adjust exercise intensity accordingly. It keeps your sessions safe, effective, and relaxing.

Instructor guidance
Weekly webinars
Daily routines
Adaptive approach

30-Day Reuvers® Program

20 days free without financial commitment

Group program starts only once a month

Join Group Program → Private Coaching

Traditional Buteyko Program

Time-tested tradition with 60+ years of proven results. Private coaching with traditional CO2 tolerance measurement and manual exercise adjustment.

Learn Traditional Buteyko →

Health & Fitness

CO2 tolerance clears the oxygen traffic jam and optimizes blood oxygen levels. It improves your vital signs, health and fitness.

Daily Vital Signs

❌ Low CO2 Tolerance

Oxygen traffic jam

Chest breathing
Higher respiratory rate
Erratic breathing rhythm
Loud, noisy breathing
Higher heart rate
Higher blood pressure
Lower oxygen consumption

✅ High CO2 Tolerance

Optimal oxygen levels

Diaphragmatic breathing
Lower respiratory rate
Stable breathing rhythm
Silent, quiet breathing
Lower heart rate
Lower blood pressure
Higher oxygen consumption

Health & Fitness Benefits

Better Oxygen Delivery

Higher CO2 tolerance enhances oxygen delivery to tissues, leading to better cellular function and energy production.

Lower Stress Levels

Better CO2 tolerance improves regulation of the nervous system, reducing anxiety and improving stress response.

Enhanced Endurance

Improved CO2 tolerance supports sustained high-intensity efforts and faster recovery between intervals.

Cardiovascular Health

Improved CO2 tolerance enhances blood vessel function, reduces blood pressure, and improves circulation.

Better Sleep Quality

Higher CO2 tolerance reduces sleep disturbances and promotes more restful and restorative sleep.

Focus & Mental Clarity

Better CO2 tolerance improves brain oxygenation, leading to better concentration, memory, and overall cognitive performance.

Better Recovery

Improved CO2 tolerance helps your body recover faster after intense exercise and physical exertion.

Immune System Support

Better CO2 tolerance helps reduce inflammation and supports overall immune system function.

Improved Breathing

Enhanced CO2 tolerance leads to more efficient breathing patterns and better respiratory function.

The Oxygen Delivery Paradox

Breathing more air doesn't mean your cells receive more oxygen from the blood

The Oxygen Delivery Paradox challenges our basic assumptions about breathing. We believe breathing more air improves oxygen supply to cells, but over-breathing can create an oxygen traffic jam. And it happens even while your blood oxygen saturation level still appears good.

Just like there are plenty of cars on the highway during a traffic jam - they're just too slow in getting to their destinations.

The Oxygen Traffic Jam

Let's trace oxygen's journey to find where the traffic jam occurs when we over-breathe.

High Airflow
Low CO2 Tolerance
Low Blood
Oxygen Uptake
High Blood
Oxygen Saturation
Low Blood
Oxygen Release
Low Cellular
Oxygen Consumption

The jam is at low oxygen uptake and low oxygen release. The jam is caused by low CO2 levels in the blood, which causes oxygen to stick too hard to the hemoglobin in the blood.

View Detailed Diagram →

The Root Cause

Too much airflow Oxygen traffic jam

Too much airflow at rest lowers blood CO2 levels, which reduces oxygen release to cells. This is a bad habit.

Oxygen traffic jam

High airflow causes lower CO2 levels, which make the arterial blood release less oxygen to cells. Old oxygen remains in the venous blood, which can pick up less fresh oxygen when it returns to the lungs.

Problem persists

Learn more in the Science section
Note: Optimal airflow quantity depends on the individual. People with certain medical conditions might require more airflow at rest.

CO2 tolerance Optimal oxygen levels

Low airflow at rest raises blood CO2 levels, which boosts oxygen release to cells. This is a good habit.

Optimal oxygen levels

Low airflow causes higher CO2 levels, which help the arterial blood release more oxygen to cells. This empties the venous blood, so it can pick up more fresh oxygen when it returns to the lungs.

Problem solved

Learn more in the Science section
Note: Optimal airflow quantity depends on the individual. People with certain medical conditions might require more airflow at rest.

The Solution

Improve your CO2 tolerance to boost oxygen release and clear the oxygen traffic jam:

Optimal Airflow
High CO2 Tolerance
High Blood
Oxygen Uptake
High Blood
Oxygen Saturation
High Blood
Oxygen Release
High Cellular
Oxygen Consumption

How it works:

  • • Enhances oxygen release to cells
  • • Increases oxygen consumption
  • • Lowers venous oxygen saturation
  • • Improves oxygen uptake from lungs
  • • Bronchodilation opens up the lungs
  • • Vasodilation improves blood flow

30-day program to clear the oxygen traffic jam and ensure optimal oxygen delivery.

Research & Evidence

How CO2 tolerance affects your health and performance

Scientific Summary

  • Improved Oxygen Release: Higher CO2 levels facilitate oxygen release from hemoglobin to cells. This raises oxygen consumption and lowers the oxygen saturation of venous blood (Bohr effect), preventing an oxygen traffic jam.
  • Improved Oxygen Uptake: The lower oxygen saturation of venous blood improves oxygen uptake by the blood from the lungs (no oxygen traffic jam).
  • Vasodilation & Bronchodilation: Higher CO2 levels trigger vasodilation (blood vessel widening) and bronchodilation (airway opening), improving blood flow and airflow through the lungs and throughout the body.
  • Breath Regulation: CO2 tolerance is the primary regulator of breathing. It controls the perceived need to breathe, allowing us to effortlessly breathe very gently, calmly and comfortably - which is a very good habit.
  • Mental Health: CO2 tolerance is linked to activation of the parasympathetic nervous system, improved relaxation, and reduced anxiety. It helps the breathing become stable rather than erratic, improving mood and reducing stress.
  • Fitness: Improved CO2 tolerance supports performance by providing more oxygen for muscles, organs and tissues. This also improves performance, endurance and recovery.
  • Multi-System Benefits: CO2 tolerance improves cardiovascular, immune, metabolic, nervous system, digestive system and other system health.

Key Research: Based on the Bohr Effect (1904), CO2 tolerance studies (Griez et al., 1987), respiratory control research (Nattie, 1999), and various studies on breath training benefits (1998-2024).

The Behavioral Benefits

Breathing Control

CO2 tolerance helps reduce chemoreceptor sensitivity, creating more stable breathing patterns and less erratic breathing responses. This leads to more efficient breathing patterns and less breathlessness.

Stress Management

CO2 tolerance helps activate the parasympathetic nervous system, promoting relaxation and reducing the "fight or flight" response. This reduces anxiety responses and improves nervous system balance.

Addressing Concerns

Addressing the most common concerns about CO₂ tolerance training. Our program includes specific exercises, daily routines, and progression tracking to help you improve your CO₂ tolerance safely and effectively.

"Reducing airflow starves the blood of oxygen"

Most people breathe 5-15 liters of air per minute at rest, but blood oxygen saturation remains at 95-100% for all. We don't need high airflow to achieve full saturation - even 5 liters per minute is sufficient. The very reason why people overbreathe is low CO2 tolerance. In fact, when CO2 levels are optimal, the blood can absorb more oxygen from the lungs because it returns to the lungs with lower oxygen saturation, ready to absorb more fresh oxygen from the lungs. For most healthy people, the limiting factors for oxygen consumption by cells are oxygen uptake into the blood (step 2) and oxygen release from blood to cells (step 3), not how many liters of air you breathe (step 1).

"But I feel better when I breathe deeply"

Deep breathing can provide real but temporary relaxation, especially during stress. However, breathing this way throughout the day creates dependency on over-breathing and reduces your natural CO₂ tolerance over time. The better goal is to feel relaxed from morning to night with normal, efficient breathing patterns that help prevent stress in the first place.

"Athletes breathe heavily, so more breathing must be better"

Athletes breathe heavily during intense exercise because they're performing at peak capacity, burning maximum oxygen and producing maximum CO2. The key difference: their blood contains high CO2 levels, which actually improves oxygen delivery. Elite athletes with high CO2 tolerance breathe more efficiently, maintaining better oxygen delivery with less breathing effort than competitors.

"CO₂ is a waste product, so removing it must be good"

While CO₂ is produced as a byproduct of metabolism, it's essential for oxygen release from blood to cells and for improving oxygen uptake from the lungs into the blood. The rate at which the blood releases oxygen for use by cells is the limiting factor, not the amount of oxygen in the air in the lungs or even in the blood. CO₂ performs essential functions in the blood that help hemoglobin release more oxygen to your cells. And after removing more oxygen from the blood, it's much easier for the blood to absorb more oxygen from the lungs as well. Removing too much CO2 actually reduces oxygen delivery to your organs and tissues. It's more accurate to think of oxygen and CO2 as teammates working together to optimize oxygen transport throughout your body.

More is coming...

We're developing more tools, practices, and devices to help you improve your CO2 tolerance and unlock your full potential.

Assessment Tools

Simple tests to measure your current CO2 tolerance levels

Training Practices

Evidence-based exercises to improve your CO2 tolerance

Monitoring Devices

Technology to track your progress and optimize training