Most people switch to mouth breathing the moment effort increases – during training, a hard meeting, or just a stressful afternoon. It feels like the natural response. It’s not.
Mouth breathing is a compensation. Nasal breathing is the baseline your body was designed for. And the gap between the two, in terms of performance, is larger than most people expect.
Why Nasal Breathing Changes What’s Possible
The nose isn’t just a filter. It’s an active part of your respiratory system with direct effects on how your body uses oxygen, manages stress, and recovers.
Here’s what happens when you breathe through your nose:
Nitric oxide production increases. The nasal passages produce nitric oxide – a molecule that dilates blood vessels, improves oxygen delivery, and has antiviral properties. Mouth breathing bypasses this entirely.
CO₂ tolerance improves. Carbon dioxide is not just a waste gas. It’s the primary trigger for releasing oxygen from red blood cells (the Bohr effect). When you breathe too fast through the mouth, CO₂ drops and oxygen delivery to the muscles and brain actually decreases – even if your lungs are full. Nasal breathing slows the respiratory rate and keeps CO₂ at functional levels. More in my previous blog post.
Heart rate stabilizes and HRV improves. Nasal breathing activates the parasympathetic branch of the nervous system, reducing heart rate and improving heart rate variability (HRV) – the metric most elite athletes and coaches now use to track recovery and readiness. Higher HRV means your nervous system is more adaptable. More adaptable means better performance under pressure.
Respiratory rate drops. Nasal breathing naturally slows the breath. Fewer breaths per minute means less respiratory effort, less energy cost, and more efficient oxygen exchange – all things that matter in sustained performance
The result: more energy with less effort. That’s not a marketing claim. That’s the mechanism.
Test Your Baseline: The BOLT Score
Before you start training nasal breathing, it’s useful to know where you stand. The BOLT score (Body Oxygen Level Test) is a simple self-test that measures your CO₂ tolerance – one of the best indicators of breathing efficiency.
How to do it:
- Sit quietly and breathe normally for a minute
- Take a normal breath in, then a normal breath out
- Pinch your nose and hold
- Count the seconds until you feel the first definite urge to breathe (not the maximum you can hold – the first natural signal)
- Release and breathe normally
What the result means:
- Under 20 seconds: breathing efficiency is low; there’s clear room to improve
- 20-30 seconds: functional range for most healthy adults
- Above 30 seconds: well-trained breathing efficiency, typical of endurance athletes who train this deliberately
Most people score between 15-25. A score under 20 correlates with higher resting respiratory rate, lower HRV, and faster fatigue onset under load. Training nasal breathing and CO₂ tolerance consistently raises the BOLT score over weeks.
Applying Nasal Breathing to Training
For athletes and high performers, the goal isn’t just nasal breathing at rest. It’s extending the threshold at which nasal breathing stays comfortable under load.
A practical approach:
- Low-intensity work: commit to nasal-only breathing for all aerobic sessions below 75% of max heart rate. It will feel slow at first. That’s the adaptation signal. Your body is learning to extract more oxygen from each breath rather than just taking more breaths.
- Recovery sessions: use the 3-minute nasal reset as a cooldown protocol to accelerate parasympathetic recovery after high-intensity work.
- Stress load: if your sport involves cognitive pressure (tactics, decision-making, competition anxiety), nasal breathing before and during that load improves focus by stabilizing CO₂ and reducing the cortisol response.
The athletes who already do this – distance runners, combat sports athletes, cyclists – don’t treat it as a wellness add-on. They treat it as a training variable, because that’s what it is.
Where to Go From Here
The shift doesn’t require a course or a retreat. It starts with noticing which way you’re breathing right now.
A simple place to begin:
- Close your mouth.
- Breathe in through your nose for 4 seconds.
- Breathe out slowly for 6 seconds.
Do this for 2–3 minutes at your desk.
That’s it.
Book a 1:1 coaching session to get a personalised breathing assessment and plan.