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Breathing BODY HANDBOOK
Breathing Β· Β§18
Nasal Breathing During Exercise
On your easy runs, close your mouth and breathe through your nose. Your pace drops about a minute per mile for a few weeks, then comes back slower and deeper. The point isn't more oxygen; it's the opposite. The nose limits your air, carbon dioxide builds up a little, and your body learns to tolerate it instead of reading a calm breath as a threat. The calmer breathing then follows you off the run β€” into your desk and your sleep.
Do Β· Daily Evidence Emerging Chapter Breathing

The nose is a worse airway, and that's the mechanism. Air through the nose meets two to three times the resistance it meets through the mouth, so breaths get slower and deeper and carbon dioxide builds up a bit more before you exhale. Most adults chronically over-breathe: too fast, too shallow, blowing off CO2 faster than they make it. The body reads that low CO2 as a mild alarm and keeps the nervous system switched on. Learning to tolerate more CO2 settles it, and the nose is the cheapest tool for the job.

A smaller second lever: your sinuses make nitric oxide, which opens the small vessels in your lungs and helps oxygen cross into the blood. Through the mouth it never gets there; through the nose it does 1.

The evidence is small but points one way. Six months of nose-only training kept peak aerobic capacity intact while cutting the air moved at hard effort by about 20 litres a minute; breathing at peak fell from roughly 49 to 39 breaths a minute 2. At an easy pace, heart rate and oxygen use barely change between nose and mouth, though the effort feels harder 3. On sprints, power is unchanged, yet the lactate spike and heart rate come in lower nasal 4. Push near all-out and it breaks: the nose can't move enough air and peak oxygen uptake drops 5. Same work, less air, at easy intensity.

On easy days, close your mouth. The real work is accepting the slower pace while your body adapts.

The arc plays out over weeks.

  • Weeks 1–3: mild air-hunger every run, pace 30–90 seconds slower.
  • Weeks 4–8: the pace comes back and the air-hunger stops. You catch yourself nose-breathing at your desk without deciding to.
  • Month 3 on: old paces return at the same heart rate, mouth closed. The pattern migrates off the run.
  • Year one: a slower resting breath, quieter sleep, less waking dry-mouthed 6, and a body slower to spike at small stressors 7.
The fine print β€” when to skip it, and what people get wrong
  • It doesn't make you faster. It keeps your capacity and makes your breathing more economical; you won't run a quicker 5K from it 2.
  • You don't get more oxygen β€” you move less air. The story is CO2 tolerance, not oxygen supply.
  • It's not a hack. It's a months-long retraining, and the first three weeks feel worse.
  • You don't actually slow down, crack to mouth-breathing within ten minutes, and never notice. A heart-rate strap catches it: if HR climbs as usual, you haven't slowed enough.
  • You use it on hard days. Races and intervals need air the nose can't deliver; you bonk and blame the method.
References
  1. 1Lundberg JO (2008). Nitric oxide and the paranasal sinuses. The Anatomical Record. link
  2. 2Dallam GM, McClaran SR, Cox DG, Foust CP (2018). Effect of Nasal Versus Oral Breathing on VO2max and Physiological Economy in Recreational Runners Following an Extended Period Spent Using Nasally-Restricted Breathing. International Journal of Kinesiology and Sports Science. link
  3. 3LaComb CO, Tandy RD, Lee SP, Young JC, Navalta JW (2017). Oral versus Nasal Breathing during Moderate to High Intensity Submaximal Aerobic Exercise. International Journal of Kinesiology and Sports Science. link
  4. 4Recinto C, Efthemeou T, Boffelli PT, Navalta JW (2017). Effects of Nasal or Oral Breathing on Anaerobic Power Output and Metabolic Responses. International Journal of Exercise Science. link
  5. 5Morton AR, King K, Papalia S, Goodman C, Turley KR, Wilmore JH (1995). Comparison of maximal oxygen consumption with oral and nasal breathing. Australian Journal of Science and Medicine in Sport. link
  6. 6Trevisan ME, Boufleur J, Soares JC, Haygert CJP, Ries LGK, CorrΓͺa ECR (2015). Diaphragmatic amplitude and accessory inspiratory muscle activity in nasal and mouth-breathing adults: a cross-sectional study. Journal of Electromyography and Kinesiology. link
  7. 7Russo MA, Santarelli DM, O'Rourke D (2017). The physiological effects of slow breathing in the healthy human. Breathe. link
  8. 8Niinimaa V, Cole P, Mintz S, Shephard RJ (1980). The switching point from nasal to oronasal breathing. Respiration Physiology. link
Related in the handbook (8)
Works well with
  • β€” You can't nose-breathe through a blocked nose; a quick saline rinse beforehand clears the airway so the practice actually works.
Related
  • β€” Nasal breathing during easy exercise is one of the most practical ways to build the CO2 tolerance this entry is about.
  • β€” Slow nasal breathing on easy runs is the same calm-breath pattern, practiced with your daily miles as the exposure.
  • β€” Mewing's real benefit is locking in nasal breathing; practicing it during easy exercise is another path to the same habit.
  • β€” Daytime nasal-breathing practice during exercise is one route to ending the nighttime mouth breathing that dries out your mouth.
  • β€” If your nose can't move enough air on easy runs, a dilator strip opens the nasal valve while you build tolerance.
  • β€” An adjacent topic in the handbook.
  • β€” Easy zone-2 aerobic work is exactly the intensity where nasal breathing fits β€” it can't move enough air for hard intervals.
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