Nasal breathing during exercise has become popular among endurance athletes, and for good reasons — but it is widely misunderstood, and there is one version of it that is genuinely dangerous. Here is what nasal breathing while running actually does, how to do it safely, and the hard line not to cross.
First, the hard line: never tape your mouth during exercise
This has to come first. Everything good about nasal breathing during exercise depends on it being voluntary and unaided — you breathing through your nose on purpose, with your mouth free to open the instant you need more air. Never tape your mouth shut, or otherwise force it closed, during any exercise. Under physical effort your body must be able to increase ventilation on demand, and taping removes that ability exactly when you might need it most — the failure mode is a respiratory emergency, not a bad workout. Mouth tape is a sleep-only tool. If you have read about athletes taping during training, that is the one thing not to copy.
Unaided nasal-only breathing, by contrast, is self-limiting and safe: the moment you truly need more air, you simply open your mouth. That is the whole safety mechanism, and it is why the voluntary version works and the taped version does not.
What unaided nasal running actually does
Done voluntarily at easy intensity, nasal-only running has real, evidence-plausible benefits:
- It builds CO2 tolerance. Nasal breathing limits airflow slightly, so CO2 rises a little — and training at that mild edge raises your tolerance for it. Higher CO2 tolerance is what makes breathing feel calmer and more efficient, at rest and in daily life. This is the main prize. (How to make nose breathing easier.)
- It naturally caps your easy-day intensity. Because you cannot sustain nasal-only breathing at high effort, it forces your easy runs to actually stay easy — which is exactly what most recreational runners get wrong by running their slow days too hard.
- It encourages diaphragmatic, rhythmic breathing and delivers the nose's usual benefits — filtering, warming, humidifying, and nitric oxide, which improves oxygen uptake. (The nitric-oxide story.)
What it will not do is let you breathe nasally at a hard race pace — that is normal and expected, not a failure.
How to do it safely
- Only at easy, low intensity. Keep nasal-only breathing for easy runs, warm-ups, and recovery paces — efforts where you can hold a conversation. This is the safe, self-limiting zone.
- Open your mouth the moment you need to. If you feel genuinely short of air, breathe through your mouth. That is the safety valve, and using it is correct, not cheating.
- Build up gradually. Start with short segments of nasal-only easy running and extend them over weeks as your CO2 tolerance improves.
- Back off when intensity climbs. As you speed up into harder efforts, switch to mouth (or nose-and-mouth) breathing. Nasal-only is a tool for the easy end of your training, not the hard end.
- A nasal strip is fine here. Unlike tape, a nasal strip only opens the airway, so wearing one to make nasal breathing easier during a run is perfectly safe.
Where the sleep connection comes in
The CO2-tolerance and nasal-airway conditioning you build with easy nasal running carry over to how you breathe at rest and asleep, making nighttime nasal breathing feel more natural. The nighttime tool for that is different: keep the mouth closed with mouth tape while you sleep — never while you train. (Train your body to nasal-breathe.)
The bottom line
Nasal breathing while running genuinely helps — it builds CO2 tolerance, keeps easy days easy, and delivers the nose's efficiency benefits — but only as voluntary, unaided nasal breathing at easy intensity, with your mouth free to open whenever you need it. Never tape your mouth during exercise. Keep the taping for sleep and the nasal-only breathing for your easy miles, and both do their jobs safely.