CO₂ Tolerance: The Secret to Staying Calm

CO₂ Tolerance: The Secret to Staying Calm

What if your ability to stay composed under pressure, whether in sport or in everyday life, came down to how well you tolerate carbon dioxide?

Most people think of Carbon Dioxide (CO₂) as a waste gas. Something to get rid of. But the truth is, CO₂ plays a vital role in how your body functions. In fact, your tolerance to rising CO₂ levels in the blood is one of the best indicators of your ability to manage stress, regulate energy, and perform at your peak.

Why CO₂ Tolerance Matters

When you hold your breath or breathe slowly through your nose, CO₂ levels in your blood rise. At first, this can feel uncomfortable or even trigger anxiety, but with consistent practice you can train your nervous system to become more efficient and less reactive.

This is important because CO₂ plays a key role in oxygen delivery. Through something called the Bohr Effect, increased CO₂ helps your red blood cells release more oxygen to your muscles and brain. The better your CO₂ tolerance, the more oxygen your body can actually use.

Improved CO₂ tolerance is linked to:

  • Better energy regulation
  • Greater focus under pressure
  • Increased endurance and stamina
  • Lower resting heart rate
  • Faster recovery
  • Reduced stress and anxiety

And you don’t need to be an athlete to benefit. Whether you're navigating a demanding job, managing kids, or simply trying to stay calm throughout the day, building CO₂ tolerance can help you feel more balanced and in control.

How to Measure Your CO₂ Tolerance: The BOLT Score

One of the simplest ways to assess your CO₂ tolerance is the BOLT test (Body Oxygen Level Test), popularised by Patrick McKeown - world-renowned breathing expert and author of The Oxygen Advantage.

How to do it:

  1. Sit comfortably and breathe normally through your nose
  2. After a regular exhale, pinch your nose and hold your breath
  3. Count the seconds until you feel the first definite urge to breathe (a diaphragm twitch or slight air hunger)
  4. Release your nose and breathe in gently through your nose

This number is your BOLT score.

What your score means:

  • Less than 10 seconds: Low tolerance, often associated with breathlessness, fatigue, and anxiety
  • 10–20 seconds: Improving, but still limited performance and stress resilience
  • 20–30 seconds: Functional range, with room to optimise
  • 40+ seconds: Excellent tolerance, a sign of efficient breathing and high stress resilience

Tip: Test your BOLT score first thing in the morning before food, caffeine, or exercise. Retest weekly to track your progress.

Ready to Train It?

Just like strength or flexibility, CO₂ tolerance improves with consistent practice. Controlled breath holds, nasal breathing, and low-intensity movement with breath awareness are some of the most effective ways to train your system.

Start with gentle breath-holds after exhaling, keeping the body relaxed and the breath quiet. Walking while holding the breath can also be a powerful way to build tolerance without strain. Focus on nasal breathing throughout the day, especially during rest, light exercise, and sleep, to gradually shift your baseline and improve respiratory efficiency.

Further Reading & References:

  1. McKeown, Patrick. The Oxygen Advantage. HarperCollins, 2015.
  2. Nestor, James. Breath: The New Science of a Lost Art. Riverhead Books, 2020.
  3. Dynamic Health & Fitness. The Performance Benefits of CO₂ Tolerance Training
  4. Lovering, A.T. & Eldridge, M.W. (2008). The Role of CO₂ in the Regulation of Breathing. Journal of Applied Physiology.
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