CO2 Tolerance Test: A Comprehensive Guide

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CO2 tolerance, a crucial aspect of our respiratory system, is often overlooked.

It refers to our body’s ability to tolerate a certain amount of carbon dioxide buildup before signaling us to expel air.

Contrary to popular belief, carbon dioxide isn’t just a waste product but plays a significant role in various physiological processes, such as maintaining blood pH and regulating breathing.

The CO2 tolerance test provides insight into an individual’s stress levels, breathing mechanics, and overall pulmonary health, as well as potential links to anxiety and mental well-being.

In this post, we will explain the CO2 tolerance test, what the results mean, and how to improve your tolerance for better performance.

Let’s dive in!

Key Takeaways

  • CO2 tolerance plays a crucial role in regulating respiration and blood pH levels.
  • The CO2 tolerance test provides valuable insights into stress levels and lung health.
  • Training to improve CO2 tolerance can improve cardiovascular health, reduce anxiety symptoms, and enhance athletic performance.

Understanding CO2 Tolerance

The Pulmonary System and CO2 Tolerance

CO2 tolerance is our body’s ability to handle a certain amount of CO2 buildup before it signals us to expel some air.

As we breathe in oxygen, our body expels carbon dioxide, a byproduct of respiration.

An increase in CO2 levels in the blood causes the dilation of blood vessels, allowing for more significant blood movement.

This process also affects oxygen absorption, known as the Bohr effect, where increased CO2 lowers blood pH, thus enhancing the body’s ability to absorb oxygen.

The respiratory system, including the lungs and diaphragm, plays a vital role in maintaining CO2 tolerance.

Related: Best CO2 Indoor Air Quality Monitors

CO2 Tolerance and The Nervous System

Not only does CO2 tolerance play a role in our pulmonary system, but it also significantly affects our nervous system.

When CO2 levels rise above a certain threshold, it acts as a trigger for our bodies to exhale, balancing the amount of CO2 in the system.

Those with low CO2 tolerance may experience increased anxiety and stress sensitivity, affecting their overall health.

CO2 Tolerance Test

A proven method to gauge and potentially improve CO2 tolerance is the Carbon Dioxide Tolerance Test (CO2TT).

This test helps to determine one’s ability to tolerate CO2 buildup, which can be used to develop specific training techniques and routines.

Four-Step Breathing Technique

  1. Initiate with Gentle Breaths: Begin by inhaling and exhaling gently through your nose. Do this three times, focusing on maintaining a calm and steady breathing rhythm. This step is crucial for preparing your body and mind for the procedure.
  2. Deep Nasal Inhalation: Next, perform a deep inhalation solely through your nose. While doing this, consciously fill your abdomen, then your upper chest, and finally your lungs. This comprehensive inhalation technique helps to fully engage your respiratory system.
  3. Start Timing on Exhale: Once you’ve fully inhaled, start a timer and begin to exhale through your nose. The key here is to exhale as slowly and controlled as possible. This slow exhalation process is essential for the effectiveness of the technique.
  4. End Timing: The final step is to stop the timer. You do this when one of three things happens: you completely run out of breath, you need to swallow, or you feel an urgent need to inhale again. This moment marks the completion of one cycle of the breathing technique.

The goal of this procedure is not just to follow the steps, but to do so with mindfulness and attention to your body’s responses.

Each step should be performed smoothly and without rush, allowing you to fully engage with the breathing process.

Refer to the table below to understand what your results mean.

> 80 secondsElite level. Indicates advanced lung adaptation, superior motor control, and minimal arousal. Suitable for high-level challenges.
60-80 secondsAdvanced level. Indicates a robust pulmonary system, effective motor control, and controlled arousal.
40-60 secondsIntermediate level. Rapid improvement possible with dedicated CO2 tolerance training.
20-40 secondsAverage level. Suggests moderate to high arousal, with potential need for breathing mechanics improvement.
< 20 secondsIdeal candidate for breathwork training. Indicates very high arousal and heightened stress sensitivity.

CO2 Tolerance Training

Breathwork for CO2 Tolerance

CO2 tolerance training is a crucial aspect of improving our body’s ability to tolerate increased levels of carbon dioxide.

One effective technique in building CO2 tolerance is practicing breathwork exercises, which focus on improving breathing mechanics and pulmonary capacity.

Related: Somatic Breathwork (Explained)

Breath-hold exercises are commonly used in CO2 tolerance training.

For example, we can perform alternating periods of breath-holds with controlled, full breaths.

This technique, known as box breathing, helps build tolerance by challenging our breath control and stress sensitivity.

Related: Neurodynamic Breathwork (Explained)

Another useful breathwork practice is nasal breathing – inhaling and exhaling through the nose while keeping the mouth closed.

Nasal breathing enhances our body’s ability to regulate blood pH, control stress, and increase CO2 tolerance.

The Role of Endurance and Performance

Incorporating CO2 tolerance training into our exercise routines can lead to significant improvements in endurance and athletic performance.

As our CO2 tolerance increases, the Bohr effect helps release more oxygen from hemoglobin, providing our muscles with the necessary energy for sustained activity.

Increased CO2 tolerance also supports aerobic metabolism and reduces the reliance on anaerobic processes during physical activities, delaying the onset of fatigue.

This adaptation enables us to maintain peak performance even as blood CO2 levels rise during intense or prolonged exercise.

In sports like freediving, where breath-hold times are critical, training our CO2 tolerance can help extend the duration before we run out of air or experience hypoxia.

The Link Between CO2 Tolerance and Anxiety

CO2 Tolerance and Stress Control

We all know that anxiety can manifest in various ways, such as hyperventilation and rapid heart rate.

One way to better understand and manage anxiety is by looking at CO2 tolerance – our ability to maintain calm and control under increased levels of carbon dioxide in our bodies.

Related: Oxygen Deprivation Training: Benefits, Risks, & Recommendations

study on CO2 tolerance and anxiety found that there is a close correlation between the two.

Those who have better control over their breathing during high CO2 levels tend to experience less generalized anxiety in their everyday lives.

On the other hand, hyperventilation – rapid, shallow breathing – is often a response to anxiety.

This can cause our bodies to expel more CO2 than necessary, leading to imbalances in our physiological responses. As a result, this can exacerbate anxiety and stress.

How To Improve CO2 Tolerance

Improving our CO2 tolerance can help us gain better control over our stress and anxiety levels.

By practicing slow, controlled breathing techniques, we can train our bodies to resist hyperventilation and maintain a more balanced emotional state under stress.

In fact, a slow breathing feasibility pilot was designed by HHP Foundation to test its effectiveness in reducing psychological and physiological stress responses for high school students.

This study is based on preliminary evidence suggesting that regular practice of slow, controlled breathing can help enhance our CO2 tolerance, leading to better stress control and reduced anxiety.


What is the purpose of the CO2 tolerance test for recovery?

The CO2 tolerance test helps to measure your body’s ability to tolerate a certain amount of CO2 buildup before it tells you to expel some air. It serves as an indicator of your breathing mechanics and pulmonary capacity.

How does CO2 tolerance impact athletic performance?

CO2 tolerance impacts athletic performance by regulating oxygen uptake and delivery. Higher CO2 tolerance levels can enhance the Bohr effect, which leads to an increased ability to absorb oxygen and better muscular functioning.

What is the difference between CO2 breath test and CO2 tolerance test?

While the CO2 breath test primarily focuses on measuring the amount of CO2 in exhaled air to diagnose certain health conditions like gastrointestinal disorders, the CO2 tolerance test assesses our ability to handle CO2 buildup in our body, providing insights into our breathing habits and pulmonary health.

How can one improve CO2 tolerance?

Improving CO2 tolerance can be achieved through various exercises and techniques aimed at optimizing our breathing patterns and lung capacity. Some ways to increase your CO2 tolerance include practicing diaphragmatic breathing, slowing down your breath, and engaging in breath-holding exercises.

What are the benefits of carbon dioxide tolerance training?

Carbon dioxide tolerance training can offer several benefits, such as improved oxygen delivery to the muscles, enhanced aerobic endurance and stamina, reduced breathlessness during physical activities, and better sleep quality. Additionally, it can help you become more resilient to stress and anxiety.

How are CO2 tolerance levels related to managing stress?

Lower CO2 tolerance levels are often associated with higher stress and anxiety states.

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About the Author

Drew Wilkins is a fitness and nutrition expert with a Master's in Biokinesiology (emphasis in Sports Science) from the University of Southern California and over a decade of experience as a personal trainer, nutrition consultant, and wellness coach. An avid surfer and soccer player, he brings a unique perspective to his research, advocating for a balanced approach to health that includes physical fitness, nutrition, and mental well-being.

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