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
- Sit quietly for 5 minutes. Take a normal breath in, then a relaxed breath out.
- Pinch your nose and count seconds until the first definite urge to breathe (not the maximum hold — the first urge).
- Release. Breathing should return to normal without gasping; if not, the hold was too long.
- 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.
Practice this with IX Coach
7 days free, then $40/month (~$1.30/day).
More practices for Nasal Breathing for Performance
- Mouth taping during sleep
Place a small strip of paper tape over your lips at bedtime to encourage nasal breathing through the night.
- Nasal-only breathing during light-to-moderate exercise
Train yourself to breathe exclusively through the nose at a pace where you can sustain it.
- Reduced-volume breathing to raise CO2 tolerance
Breathe slightly less than your body demands — a mild air hunger — to recalibrate the CO2 set point.
- Nasal humming to boost nitric oxide
Hum for 1-2 minutes after waking to flood the sinuses with nitric oxide before it is inhaled.
- Breathe light to breathe right (nasal at rest)
Maintain habitual nasal breathing at rest by consciously catching and correcting mouth-breathing episodes throughout the day.
Related concepts
- Box Breathing, Made Practical
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- Coherent Breathing, Made Practical
The five-breaths-per-minute method, why coherence matters, and how to build a daily practice
- The Wim Hof Method, Honestly Assessed
What the research actually shows, what it doesn’t, and how to do it safely
- Nostril Breathing: Pranayama for Calm and Focus
Alternate nostril breathing, single-nostril techniques, and the physiology behind them