A Trained Ability
CO₂ Tolerance
A trained ability to stay calm and in control as CO₂ rises. The higher your tolerance, the more oxygen your blood delivers, and the less air you need to breathe. The mechanism that clears the oxygen traffic jam and drives oxygen efficiency.
What CO₂ tolerance is
CO₂ (carbon dioxide) isn't just a waste product. It's a signaling molecule. When CO₂ levels rise in your blood, it triggers your blood to release oxygen to your cells. This is called the Bohr effect, and it's been in every physiology textbook since 1904.
CO₂ tolerance is your body's ability to maintain higher CO₂ levels without triggering the urge to breathe. The higher your tolerance, the more oxygen your blood delivers to your cells.
Most people have low CO₂ tolerance. They breathe more than they need to, which keeps CO₂ low and oxygen delivery inefficient. Training CO₂ tolerance reverses this. It clears the oxygen traffic jam and allows blood to release more oxygen at the cells.
CO₂ tolerance and the oxygen traffic jam
When CO₂ levels in the blood are low, hemoglobin holds onto oxygen too tightly. This is the oxygen traffic jam: your blood is full of oxygen, but your cells cannot access it. The traffic jam is directly caused by low CO₂ tolerance.
As CO₂ tolerance improves, the blood maintains higher CO₂ levels at rest. Hemoglobin releases oxygen more freely. The jam clears. More oxygen reaches the cells, while breathing less air.
How you train it
In breathing training, three things raise CO₂ tolerance most directly:
- Breath holds. Breath holds are the most direct way to train CO₂ tolerance. Each hold extends your comfort zone a little further.
- Reduced breathing. Gentle, quiet breathing builds CO₂ tolerance gradually. Less intense than holds, but consistent and effective over time.
- Relaxation. Stress reduces CO₂ tolerance by driving up breathing volume. Relaxation supports it. The deeper you relax, the more oxygen your cells receive.
Lifestyle also plays a role, but these three are the core training tools.
The Reuvers® program combines all three in a structured way. You can start with the app on your own, join a Foundation Weekend or Immersion Weekend for guided training, and stay consistent through the Club. The Club is a space to practice, watch instructional videos, and talk through the experience with others. Whether you prefer to work under guidance or explore on your own, experiment with the exercise, find what works best for you, and build a lasting habit.
The evidence
CO₂ tolerance training targets oxygen efficiency directly, which produces much larger effects than generic breathing exercises. The mechanism has been studied for over 60 years across multiple countries.
The deeper you relax, the better you perform.