Breath holds and reduced-ventilation techniques produce mild hypercapnia. Repeated exposure raises the threshold at which the chemoreceptors trigger urgent breathing, which is what "improved CO₂ tolerance" means.
Elevated CO₂ in the blood. Deliberate mild hypercapnia is the training stimulus in CO₂ tolerance work.
Breath holds and reduced-ventilation techniques produce mild hypercapnia. Repeated exposure raises the threshold at which the chemoreceptors trigger urgent breathing, which is what "improved CO₂ tolerance" means.
See also
Learn · Science
CO₂ Tolerance: The Real Limiter in Breathwork
The urge to breathe is driven by CO₂, not oxygen. Train that urge and every breathwork practice — plus a lot of your resting physiology — improves.
Learn · Techniques
The Buteyko Method: Breathing Less, on Purpose
Konstantin Buteyko's Cold-War-era method argued that most modern breathing is over-breathing. The core practice — deliberately reducing minute ventilation — has held up better than its origins suggest.