Co2 Tolerance 4 Runners

I’m gonna let you in on a secret to not being out of breath while running.

Wait, I can run without feeling gassed, winded, and out of breath?

Yes you can!

Running is tiring, as it should be. Attempt to run farther and faster and you are sure to get more winded. There are many variables to improve this, such as pacing yourself, staying hydrated, fueling your body, getting adequate sleep, and managing your stress. The one variable that’s often forgotten and has a valuable impact on both training and recovery is breathing.

The two main fuels for your muscles (and your brain) are oxygen and glucose. So one would think that huffing and puffing for more intake of oxygen would help the muscles, right? Wrong!

Getting oxygen to your muscles requires the balance of both Oxygen and Carbon Dioxide (Co2) in the blood.

The best way to get this balance is through slow rhythmic nasal breathing and training your tolerance to Carbon Dioxide. Training your breathing can lead to less physical fatigue because your heart doesn’t have to work as hard. Many athletes uses a heart rate monitor during training to help them stay in the optimal zone and improve speed and endurance.

But, here’s the secret…control your breath rate, control your heart rate!

Test Your Co2 Tolerance Here

Breath Control

The body’s tolerance to Co2 is what determines how often and how fast you breathe.

Humans inhale oxygen and exhale carbon dioxide (Co2) and we have long been taught that carbon dioxide is a waste product (unless you are a plant).

However, it turns out you don’t exhale all of it. The body actually has important uses for it. The need for more oxygen is not why you breathe. Instead it is the body’s chemo-receptors that detect Co2 and prompt breathing so you don’t suffocate. Co2 is valuable for many physiological functions in the body and when the body is intolerant to it things go awry. (Note: There are medical conditions resulting from too much Co2 in the blood stream in people with COPD — this is not what I am addressing here.)

When exercise makes you gasp for air or breathe too heavily, you are getting rid of the much needed Co2 and not absorbing oxygen well. The usual answer is to slow your pace. But you can train your breathing to be slow and controlled during exercise which keeps your heart rate from rapidly rising. This is how you can gradually increase your pace without feeling so winded. 

Carbon dioxide is a metabolic stress messenger. So whether you are stressing your body during exercise or feeling stressed emotionally, your breath will change. Being able to keep the breath regulated is how you train stress resilience in sports and in life. 

Convinced yet?

Benefits of Carbon Dioxide

If you want to improve running performance (training + recovery) then learn how to breathe more efficiently and how to tolerate carbon dioxide. Control your Co2 levels which will control your breath rate.

  1. Co2 makes your muscles more efficient. When you exercise, blood flow goes to the muscles and delivers oxygen. In order to offload the oxygen into the muscle, Co2 is needed to drive it in. How much oxygen we breathe in doesn’t matter if it can’t be used properly in the muscles. This is called the Bohr Effect and was discovered in 1904. The amount of oxygen you inhale isn’t the determining factor in how well your muscle uses that oxygen, Co2 is.
  2. Co2 improves recovery and fatigue after exercise. The key to eliminating metabolic acidosis and repairing muscle damage after exercise is carbon dioxide. Co2 is an antioxidant and prevents oxidative stress.
  3. Co2 improves performance and endurance.  The two necessary fuels for muscle efficiency are glucose and oxygen. It’s not as simple as breathing in more oxygen to help the muscles perform well. What typically doesn’t get explained in this process is the body’s necessary use of Carbon Dioxide (Co2). When you run, your heart rate and breathing quicken as a normal response to the body moving faster. Nasal Breathing during exercise improves the Co2 tolerance and leads to greater Heart Rate Variability and easier recovery time. Your fitness is largely defined by your ability to tolerate carbon dioxide levels in order to use oxygen efficiently — which seems counterintuitive to what we’ve been taught all these years.
  4. Co2 boosts metabolism. Increasing Co2 levels helps burn more fat and improves metabolic conditions. Fat is actually converted to carbon dioxide and water. So when you burn fat it is lost in the air you exhale as well as in sweat and urine. This is how the metabolic rate works. Muscles being used need Co2 and O2 to be effective and burn more fuel.
  5. Co2 Tolerance relates to overall physical health. A better tolerance of Co2 is shown to be a predictor of a healthy physiology since it is a marker of stress on the system. Consider sleep apnea and how that wreaks havoc on one’s health. Sleep apnea is the loss of oxygen during sleep as breathing stops and starts over and over again. Mouth breathing contributes to this as it exhales too much Co2 and inhales unfiltered air. Nasal breathing has been shown to Improve HRV, oxygen saturation, blood pressure, brain health, and inflammatory markers, among others.
  6. Co2 Tolerance affects mental health. CO2 Tolerance has been highly studied in the field of Psychology and is found to be an indicator of distress tolerance and self regulatory capacity. An example of high emotional reactivity would be panic attacks with fast shallow breathing and rapid heart rate. Co2 builds up quickly with rapid shallow breathing (hyperventilating).  Deep breaths can help calm someone, but it is the body’s ability to tolerate the carbon dioxide that makes the biggest difference.
  7. Co2 improves Brain health. Doctors use Co2 therapy for Epileptic seizures. Administering Co2 has been shown to suppress the convulsion during the acute seizure attack within 1 minute. One other fascinating fact is there are carbon dioxide chemoreceptors in the cerebellum, the part of the brain that regulates balance. So breathing affects balance and the vestibular system adjusts breathing. Fascinating!
If you’re a runner who wants to improve your physical endurance and performance, then testing and training your Co2 tolerance is a non-negotiable. Download two free videos to learn better breathing techniques for runners.


Are you a physical therapist wanting to implement CO2 tolerance with your patients?

Click here for a webinar titled Co2 tolerance in Physical Therapy. 


For more fun breathing news, subscribe to my connected breath monthly newsletter here. 


Test Your Co2 Tolerance Here

Access these videos and more here

Simply fill out the form below, and you’ll receive instant access to some great resources to help your running performance.

"*" indicates required fields

This field is for validation purposes and should be left unchanged.