The Science of CO2 Tolerance: Why It Matters for Your Health and Performance

Most people have never heard the term CO2 tolerance, let alone consider how it affects their health. We breathe in oxygen, breathe out carbon dioxide, and repeat. Simple, right? Not quite.

CO2, or carbon dioxide, often gets a bad reputation as the waste product of breathing. But in reality, it's one of the most important elements in how your body uses oxygen. If you've ever felt out of breath during exercise, anxious for no reason, or constantly tired despite good sleep, there’s a chance your CO2 tolerance has something to do with it.

In this blog, I want to break down what CO2 tolerance is, why it matters more than you might think, and how I help people train their bodies to use oxygen more efficiently, stay calm under stress, and recover faster.

What Is CO2 Tolerance?

CO2 tolerance is your body’s ability to handle rising levels of carbon dioxide in the bloodstream. It plays a direct role in how your brain regulates your breathing and how your muscles receive oxygen. When you hold your breath or engage in physical activity, CO2 levels increase. Your brain responds by telling you to breathe. This reaction is stronger or weaker depending on how tolerant your body is to CO2.

If your CO2 tolerance is low, you’ll feel short of breath quickly. You might breathe fast and shallow even at rest, and you may experience higher stress or anxiety levels. On the other hand, if you have high CO2 tolerance, your breathing stays calm and efficient, your endurance improves, and you recover faster after intense effort.

Why does this matter? Because CO2 helps release oxygen from the blood to your tissues. This is known as the Bohr effect, and it's how your body actually makes use of the oxygen you inhale. Without enough CO2 in the blood, hemoglobin holds onto oxygen instead of releasing it where it's needed. That means poor oxygen delivery and lower performance, even if you're breathing plenty of air.

Signs of Low CO2 Tolerance

There are some clear signs that your CO2 tolerance could use some work. You might notice things like:

• Getting winded easily during workouts or stairs

• Feeling lightheaded or dizzy after holding your breath

• Chronic mouth breathing or over-breathing

• Panic or anxiety during moments of stillness

• Difficulty focusing or recovering from exertion

A useful self-assessment I recommend is the exhale test, which I describe in The Language of Breath. After a gentle, normal exhalation, how long can you comfortably hold your breath until you feel the first distinct urge to breathe? It should feel like a controlled challenge, not a struggle. This gives you a real-world indicator of how well your body tolerates rising CO2.

Why Athletes and High Performers Care About CO2 Tolerance

Athletes have known for a long time that how you breathe affects how you perform. High-level training programs often include breathwork drills to build better respiratory efficiency. But it's not just about sports. Better CO2 tolerance helps with mental resilience, emotional control, and energy management in everyday life.

Studies have shown that improved CO2 tolerance leads to better oxygen delivery, lower heart rates during exercise, and faster recovery. Research shows that structured breath training can reduce markers of inflammation and oxidative stress post-exercise, which means less soreness and quicker returns to peak condition.

Even if you're not an athlete, this matters. Whether you're managing a busy schedule, dealing with high-pressure moments, or just trying to improve your focus and energy, increasing CO2 tolerance can help you show up more fully and feel more balanced.

Training CO2 Tolerance: Where to Start

The most effective way to improve CO2 tolerance is to gradually expose your body to slightly elevated levels of carbon dioxide and train yourself to remain calm. It’s not about pushing hard or holding your breath to extremes. It’s about consistency, awareness, and learning to listen to your body's signals.

I often recommend starting with nasal breathing. It’s one of the simplest and most effective techniques. Breathing through your nose slows your breath rate, helps you retain more CO2, and improves oxygen uptake. Try it during daily walks or light exercise and notice how your endurance shifts over time.

Another effective tool is breath holds after a regular exhale. These can help condition your body to tolerate higher CO2 without triggering stress. Begin gently. After a natural exhale, hold your breath until you feel the first clear signal to breathe, then resume with slow nasal breathing. Over time, this builds resilience without overwhelming the system.

Slow, rhythmic breathing also plays a role. Practicing a 5:5 or 5:6 inhale-to-exhale ratio can help balance your nervous system while reinforcing CO2 tolerance. This is especially helpful in the evenings to support recovery and better sleep.

As you practice these techniques, you’ll likely notice your breath becoming quieter, slower, and more stable-even during challenging moments.

My Approach to Breath Training and CO2 Tolerance

In my teaching and coaching, I focus on making breathwork accessible and effective for anyone, no matter their background. Breath training doesn’t need to be complicated or mystical to change your life. It just needs to be practical, consistent, and grounded in how your body actually works.

My approach goes deep into the functional aspects of breathing, especially how we use CO2 to support our physical and mental performance. In my coaching programs and courses, I help people build personalized breathing strategies that fit their lives, whether they’re athletes, professionals, or simply looking to feel better.

CO2 tolerance is a skill, and like any skill, it improves with practice. I’ve seen people improve their sleep, reduce anxiety, enhance focus, and recover faster just by learning to breathe with more awareness and structure.

Final Thoughts: Why It’s Worth Paying Attention to Your Breath

Your breath is one of the most powerful tools you have to improve your health, performance, and peace of mind. CO2 tolerance may not be a term you hear often, but it plays a huge role in how your body uses oxygen and manages stress.

If you’re looking for ways to perform better, stay calm under pressure, or just feel more in control of your body and mind, improving your CO2 tolerance is a great place to start.

To learn more about how I teach breath training and to explore my courses and programs, visit jessecoomer.com. You'll find tools to assess your breath, build CO2 resilience, and integrate breathwork into your daily life in a way that’s simple, safe, and effective.

It all starts with a breath. And when you begin to pay attention, everything starts to shift.