How to measure CO2 tolerance?

To measure CO2 tolerance, Andrew Huberman describes a simple test that can be done upon waking. Here is the step-by-step process as explained by Andrew Huberman:

1. Upon waking (and after using the restroom if needed), avoid engaging with your phone.
2. Inhale deeply through your nose four times and exhale through your mouth.
3. On the fifth inhale, fill your lungs as much as possible, expanding your stomach to engage your diaphragm.
4. Start a timer and exhale slowly through your mouth as if you were blowing through a tiny straw, aiming to release air as slowly as possible.
5. Stop the timer when you can no longer exhale any more air.

This test measures your carbon dioxide tolerance, indicating how well your nervous system—specifically the calming, parasympathetic arm—is functioning and tracking your ability to recover from physical efforts or stress. The discard time can vary, with times closer to two minutes indicating a good state of recovery. It is advised to track your CO2 discard times consistently and take note of any changes. If your discard times are dropping, it may signal you are not fully recovering 1 2 3 4.