Breathing & CO2 Tolerance
Measure and train how well you handle carbon dioxide. Andy Galpin's CO2 tolerance test doubles as a free recovery gauge, and nasal plus box breathing builds the control that steadies performance and stress.
Most people think breathing is about getting oxygen in. Galpin's framing flips it: the limiter is usually how well you tolerate rising carbon dioxide, and that tolerance is both trainable and a useful readout of your nervous system. The CO2 tolerance test (how long you can slowly exhale after a set of breaths) gives a zero-cost recovery and stress gauge, similar in spirit to HRV. Default to nasal breathing, train mechanical control with box breathing, and use breath to hold composure in hard efforts.
Why it works▼
Measure your controlled exhale
It is a fast, free gauge of recovery and nervous-system readiness.
Read the number as a trend, not a verdict
Like HRV, it is most useful tracked against yourself over time.
Breathe through your nose by default
Nasal breathing is more efficient and supports better posture and breathing mechanics.
Practise box breathing to lower resting rate
Builds mechanical control over breathing and reduces resting respiratory rate.
Manage breathing in hard efforts
Composed breathing prevents the early over-breathing that wrecks later efforts.
Track the test alongside training
It flags under-recovery before it becomes injury or burnout.
- Endurance athletes and lifters
- Anyone wanting a free recovery gauge
- People who default to mouth breathing
- Those who panic-breathe under exertion or stress
- The CO2 tolerance test is a useful trend tool, not a validated clinical measure; treat it as directional and compare only to your own baseline
- Breath-holds and intense breathwork are not for everyone: avoid them in pregnancy, with cardiovascular or seizure conditions, and never do breath-holds in or near water
- Build gradually; if controlled breathing makes you lightheaded, stop and breathe normally
- Educational only, not medical advice
- July 3, 2026 Protocol published.
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Not medical advice. This page is for education only and is not a substitute for professional medical care. Consult a qualified clinician before changing your health routine.
Independent curation. YourProtocol.ai is an independent platform. This protocol is based on the publicly available work of Andy Galpin and is not created, reviewed, endorsed by, or affiliated with Andy Galpin or Parker University / Performance.