BOLT score — measure your CO2 tolerance

The Body Oxygen Level Test gives you a repeatable number to track nasal breathing progress.

Why it works

The BOLT score measures the duration of comfortable breath-hold after a normal exhale — a proxy for CO2 tolerance. A low score (under 20 seconds) correlates with habitual over-breathing and respiratory-related performance limits. Tracking it over weeks turns an invisible physiological parameter into actionable feedback.

How to do it

1. Sit quietly for 5 minutes. Take a normal breath in, then a relaxed breath out.
2. Pinch your nose and count seconds until the first definite urge to breathe (not the maximum hold — the first urge).
3. Release. Breathing should return to normal without gasping; if not, the hold was too long.
4. Test at the same time of day, at rest. Log weekly.

Evidence

The BOLT score is a clinical tool used in Buteyko practice, with some correlation to respiratory chemosensitivity data. It is not validated against gold-standard respiratory measures in large trials. (mechanistic)

Correlation with VO2 max or athletic performance has not been established in independent, large-scale studies. Treat it as a personal progress marker, not a clinical diagnostic.

Common mistake

Holding as long as possible rather than stopping at the first urge to breathe — this inflates the number and measures anaerobic tolerance rather than CO2 sensitivity.