Maurice, Maria and Dennis uses CO₂ as a booster for performance, recovery, sleep and mental strength. Also Hypoxic Training with less Oxygen in the air, like High Altitude Training is a big thing out there for top athletes. Erlin Haaland does it.

Our breath itself is a powertool for everybody, and the athletes environment has found that since years now.

Nose breathing, optial mechanics for breathing, and breath-hold exercises to lower blood oxygen saturation and increase carbon dioxide (CO₂). This is a powerful stimulus that delays lactic acid and fatigue, and results in improved oxygen-carrying capacity.

Athletes are smart. They understand that every single percentage point of improvement can make the difference - and help pave the way to the top.

With this blog post, I simply want to share some inspiration from my work with CO₂ as an active part of Breathwork. For me, CO₂ is a very important part of the biomechanical work I do around breathing and the development of our breath skills.

What is hypoxic training?

Shortly, hypoxic training means exercising with a lower availability of oxygen than under normal conditions. It is also known as altitude training. In other words, there is less oxygen available and a higher proportion of CO₂ relative to oxygen.

In this first video clip, you can see how one of the world’s best football players uses hypoxic training as an important part of his foundational training.

Follow the story of Norwegian footballer Erling Haaland below.

What is CO₂ therapy?

CO₂ therapy is closely related to hypoxic training. Here, extra CO₂ is added to the air you breathe or the environment you are in. This differs from hypoxic training, where there is less oxygen available and therefore a higher proportion of CO₂ relative to oxygen.

With CO₂ therapy, CO₂ is actively added, meaning the body is exposed to higher levels of CO₂ that it needs to tolerate.

Regardless of the method, this triggers a wide range of physiological responses that can have an important impact on blood circulation, oxygen uptake, recovery, and healing.

I won’t go too deeply into the differences or try to determine which approach is better than the other. But the method that is clearly the most accessible to all of us is CO₂ therapy. It can even be practised at home.

You can learn more about CO₂ therapy by listening to this podcast episode I made with Anders Olsson.

Dennis shares his experience with CO₂ therapy

Dennis Frisch is a Danish Body Nerd, Physical Trainer, Brain-based Exercise therapist.

Listen to a Danish and translated talk from Dennis about his experiences with Cardihaler CO₂ therapy.

Using the Cardihaler, you can improve your brain function because more oxygen actually gets to the brain, even though you're not breathing anymore. Over the past 5-6 months, I've been working with a tool that almost no one uses, as part of the breathing practice I use with myself and my clients.

As part of the resetting practice, where we work on calibrating the nervous system, so that it is finely tuned so that it can autoregulate. That is, it can adjust itself and turn it up and down.

And there is almost no one that I have heard of who uses this tool. The tool we are talking about is a Cardihaler and simply a tool where we can increase the amount of CO₂ we breathe in in a dosed form.

Thereby increasing our tolerance to CO₂, so that the body and brain feel more comfortable in an environment with more CO₂. And that means that our stress threshold increases to that extent.

That means that we can autoregulate much more easily, that we can breathe less and perform more. I and my clients have seen to a great extent that our breathing rhythm decreases.

We can run longer on less breathing. It is easier to switch from mouth breathing to nose breathing, and the breathing frequency decreases, which harmonizes with this element of frequency breathing, where what we know is that if we breathe 5-7 times a minute, that is where our system finds a balance in what is called heart rate variability, so that our recovery is better.

So that we can better land a level for our nervous system and immune system and hormonal system, that it can keep up with what we are doing. All we do is a 10-20 minute protocol a couple of times a week, as a way to down-regulate, as part of the practice that you may already be doing, or as an extra layer.

So are you someone who works with your nervous system? Do you want to have more peace in your body and head? Do you want to be better at auto-regulating? Do you work with cardio sports, and do you want to get more out of your breathing?

So this is a formidable way to go about it. Look at the intelligent body. Write to me if you have any questions about how I use it, and if you want to know more about some specific cases where I have seen improvements.

German football player shares his experience with Cardihaler

Since I’ve been using the Cardihaler nearly every day, I’ve noticed much less muscle tightness after training sessions and fewer problems with some of my old injuries. 

I also recover so much better. I’ve been using WHOOP for 3 years, and my HRV has never been particularly high. Since I started using the Cardihaler, I’ve been getting better HRV results, and my Recovery Score has already improved a lot — even when I have two hard training sessions in one day. My Recovery Score is consistently higher the next day when I’ve used the Cardihaler the day before. 

I’ve also noticed quite a few benefits in my daily life: I feel less stressed in certain situations, more calm, and mentally more resilient. 

Such a big impact on my life!

Danish women´s padel champion shares her experience

Maria plays padel at the absolute highest level at an age when most people would have stepped back from competitive sport.

She is currently the highest-ranked Danish woman both nationally and internationally (around the top 200 in the world), Danish Champion in 2024, 2025, and 2026, and one of the passionate driving forces behind the development of padel in Denmark.

Here, she shares a little about her experience using CO₂ (you can hear more in the podcast). Maria is a particularly dedicated user of Cardisuit CO₂ therapy.

A little history: Carbogen – The therapy medicine forgot

Carbogen is a gas mixture — typically 5% carbon dioxide and 95% oxygen (although the ratio can vary). The name comes from the combination of carbon dioxide and oxygen. In other words, this was CO₂ therapy more than 100 years ago.

By 1900, carbogen was in regular clinical use. It was used, for example, to make anesthesia safer and help prevent surgical collapse. It was also used in cases of pneumonia, carbon monoxide poisoning, asthma, neonatal resuscitation, psychiatric conditions, and serious cardiovascular conditions.

This was not a fringe treatment. It was an established medical gas therapy, available in hospitals, studied in scientific journals, and taught in medical schools.

Yandell Henderson, a Yale physiologist, was one of its most prominent advocates. He referred to CO₂ as “the chief hormone of the entire body” and spent decades demonstrating that adding CO₂ to oxygen could transform it from a supportive gas into a therapeutic one. His work was published in leading journals, his findings were replicated, and carbogen was used as medicine.

Then it essentially disappeared.

Today, gases such as oxygen, heliox, and nitric oxide are used in medicine, but not carbogen. It could not easily be patented, since you cannot simply own a mixture of 5% CO₂ and 95% oxygen. So you could say that carbogen had no commercial champion. No company had a strong financial incentive to fund the large-scale trials that would cost millions while the product itself would generate very little revenue.

Carbogen didn’t fail a major clinical trial — it never really got the opportunity to prove itself through one.