CO2 tolerance testing for recovery

CO₂ tolerance testing offers a quick, no-cost way to gauge breathing control and possible recovery by timing a slow, controlled exhale after several deep breaths.

• How to do it: Take four deep breaths, inhaling through your nose and exhaling fully each time. On the next deep inhale, start a timer and slowly exhale through a small opening in your mouth, as if through a tiny straw. Stop timing when you can no longer exhale—not when your lungs are empty and you are holding your breath. 1
• How to read the time: Under about 30 seconds can indicate you may not be recovered; 30–60 seconds is described as a “green zone” for doing more physical work; and 65–120 seconds is described as a range in which the nervous system has almost certainly recovered. 2
• What it tells you: The test is a free, trackable indicator of diaphragm control and the ability to engage the calming, parasympathetic nervous system. It can help monitor stress and recovery, but it is described as a rough measure; CO₂ tolerance has less published research than better-established recovery measures such as HRV. 3 4