Improving your CO₂ tolerance can help you optimise both your physical and mental performance. Is a new PB as easy as breathing in and out?
Let’s try something: wherever you’re reading this, sit a little taller and inhale and exhale through your nose. Now open your phone’s stopwatch. At the end of your next exhalation, start the timer and hold your breath. As soon as you feel the urge to breathe, inhale and stop the clock.
What was your time? Mine was 19 seconds, and we’ll get into what’s ‘good’ and ‘bad’ in a minute. This is your BOLT (body oxygen level test) score, or one way to measure carbon dioxide (CO₂) tolerance, from Patrick McKeown, CEO of the breathwork training programme Oxygen Advantage. Much like tracking your heart-rate variability or VO₂ max, CO₂ tolerance is a metric of fitness and overall health that you might be overlooking. And we can all benefit from tracking this stat. ‘Breathing influences every system and cell in the body and can either help or hinder your fitness goals,’ says PJ Nestler, director of performance for the training platform XPT. ‘Your breathing is a weakness or a weapon.’ While it’s true that high CO₂ tolerance can help you run faster and longer, perhaps more importantly, a poor tolerance is linked with a variety of ailments.
The bigger your number, the more stress (of any kind) you can handle, says Emily Hightower, master yoga teacher and coach at the members-only training platform SH//FT. A quick refresh of respiratory physiology explains why. ‘The whole purpose of our respiratory system is to keep a balance of two gases – carbon dioxide and oxygen – in the body,’ says Nestler. While CO₂ travels through blood, it triggers oxygen to be released from the red blood cells to your tissues, muscles, brain and organs. A higher CO₂ tolerance means this process is more efficient.
You can see the impact in performance. Let’s say you and I are running sprint intervals side by side on a treadmill at the same pace. If your CO₂ tolerance is higher, you’ll be able to push for longer during work intervals. You may suspect there’s a link to VO₂ max – the maximum amount of oxygen you can use in exercise. As you increase your CO₂ tolerance, you can improve your VO₂ max, too.
But CO₂ tolerance goes way beyond PBs. When you work on it with breathing practices, you can feel it in your reaction to stress as well. People who train their noses have more awareness and control when stressed. Think of it like this: you’re at the start line of a race after a night of poor sleep and tummy trouble. Not ideal, but if your CO₂ tolerance is higher, you’ll manage better. Read on for how to assess your own CO₂ toleranc
