Summary
Brad Kearns delivers a solo deep-dive into nasal parasympathetic breathing and the science of CO2 tolerance. He walks through the BOLT test and Sustained Exhale Test as practical assessments, sharing his personal journey from a sub-20-second BOLT score to consistently hitting 35 seconds through dedicated practice. Brad explains the counterintuitive concept that we already have sufficient blood oxygen saturation and that the real bottleneck is CO2 tolerance, which dictates how efficiently oxygen is delivered to working muscles. He also covers the difference between the BOLT test and Brian McKenzie's Sustained Exhale Test, and provides actionable guidance on minimal breathing during both daily life and exercise.
Key Points
- The BOLT test measures CO2 tolerance by timing how long you can comfortably hold your breath after a normal exhale, with 20 seconds as minimum and 40 as the target
- Blood oxygen saturation is typically near 100% already, so bigger breaths do not increase oxygen delivery
- CO2 tolerance is the real bottleneck for oxygen delivery to working muscles via the Bohr effect
- Brad improved his BOLT score from under 20 seconds to 35 seconds in just a few weeks of nasal breathing practice
- The Sustained Exhale Test (Brian McKenzie's alternative) measures how long you can slowly exhale after a full inhale
- Minimal breathing through the nose activates the parasympathetic nervous system, reducing stress
- During exercise, brief mouth breathing is acceptable but the goal is to return to nasal breathing quickly
Key Moments
How the BOLT test measures CO2 tolerance
Brad explains the BOLT test procedure step by step, emphasizing that it measures how much carbon dioxide can accumulate before the urge to breathe.
"Body Oxygen Level Test measures how much carbon dioxide can accumulate until you feel the urge to take a breath. So here's what you do. You breathe normally through your nose for a few cycles. Don't take a bigger breath than normal."
Brad's personal BOLT score improvement journey
Brad shares how he improved from a sub-20-second BOLT score to consistently hitting 35 seconds in just a few weeks of nasal breathing practice.
"I was under 20 seconds, a pathetic under 20 seconds for my first few bolt tests. And in just a few weeks of practice, I was at a minimum of 20 seconds."
Why bigger breaths do not increase oxygen delivery
Brad quotes Patrick McKeown explaining that blood is already nearly fully saturated with oxygen, making bigger breaths futile for increasing oxygenation.
"It is physiologically impossible to increase the oxygen saturation of the blood by taking bigger breaths because the blood is almost always already fully saturated. It would be like pouring more water into a glass that's already filled to the brim."
