For a runner, breath training is a lever on CO₂ tolerance, breathing economy and comfort — not on your VO₂max ceiling. It can make a given pace feel calmer, quiet the early air hunger that wrecks your form, and lower how hard you have to breathe at submaximal effort. What it will not do is raise the size of your engine. Once you separate those two claims, breath work becomes a genuinely useful tool instead of a magic pill.
Why breathing can limit a run — and what is actually trainable
Two things happen to your breathing when you run that have nothing to do with your legs.
The first is air hunger — the urge to breathe harder that arrives well before your muscles are actually starved of oxygen. Just like in a breath hold, that urge is driven mostly by rising carbon dioxide, not by falling oxygen. A runner who panics at the first wave of air hunger tenses up, over-strides and burns energy fighting their own diaphragm.
The second is over-breathing — dumping far more air than the effort requires, in short, shallow, upper-chest gulps. It feels like you are working hard for your oxygen. Mostly you are just moving stale air in and out of the top of your lungs.
Neither of those is your VO₂max. Both are habits and tolerances, and both are trainable. That is the honest promise of breath work for runners: not a bigger engine, but a calmer, cheaper, more controlled way of feeding the one you have.
CO₂ tolerance vs VO₂max — the myth-check
This is where most breath-training marketing quietly overreaches, so let’s be precise.
A 2025 randomised controlled trial put recreational runners through a short functional-breathing program and measured what changed. The result is the cleanest myth-check you could ask for: resting breath-hold time improved significantly in the breathwork group and barely moved in the control group (+11.7 s vs +1.9 s; p = 0.04, with a large effect size, d = 1.13). But VO₂max did not differ between the groups (Sports, 2025, DOI 10.3390/sports13020031).
Read that twice. The breathing program clearly built CO₂ tolerance — that is exactly what a longer breath hold measures. It did not enlarge the aerobic engine. So if a program promises breath drills will raise your VO₂max, the evidence says otherwise. What breath training reliably moves is your tolerance for the CO₂ signal and how comfortable a given pace feels — which is worth having, as long as you buy it for what it is.
| Claim | What the evidence supports | Verdict |
|---|---|---|
| ”Breath drills raise VO₂max” | No group difference in the runner RCT | Myth |
| ”Breath training improves CO₂ tolerance” | Breath-hold +11.7 s vs +1.9 s (p = 0.04, d = 1.13) | Supported |
| ”Nasal breathing is more efficient at easy pace” | Lower VE/VCO₂, slower breathing, higher end-tidal CO₂ | Supported |
| ”You can breathe only through your nose at race pace” | Nasal-only impairs peak capacity via ventilatory limit | Myth |
Nasal breathing: what the evidence really shows
Nasal breathing is the other claim that gets stretched. The truth is genuinely good — just bounded.
At rest and at easy-to-moderate effort, nasal breathing is more efficient. A 2024 study found that breathing through the nose lowered the ventilatory equivalent for CO₂ (VE/VCO₂), lowered breathing frequency and raised end-tidal CO₂ across every group tested, including healthy controls (Frontiers in Physiology, 2024, DOI 10.3389/fphys.2024.1380562). In plain terms: calmer, slower, more economical breathing for the same submaximal workload. That is exactly the state you want on an easy or base run.
But there is a ceiling. When researchers pushed people to peak effort using exclusively nasal breathing, it was fine at rest and submaximal intensities but impaired peak exercise capacity because the nose cannot move enough air — a ventilatory limitation, not a lack of willpower (PLOS One, 2025, DOI 10.1371/journal.pone.0326661).
So the rule writes itself: nose for easy and base runs; open the mouth as intensity climbs. Forcing nasal-only breathing at race pace does not make you tougher — it caps your ability to shift air right when you need the most. Use nasal breathing where it pays, and stop treating an open mouth at threshold as a failure.
A dry protocol for runners
You train CO₂ tolerance off the road, then let it show up on it. None of this needs water, and none of it belongs at max effort.
CO₂ tolerance at the same pace
Drag the slider from low to high CO₂ tolerance and watch what happens at one unchanged running pace: the same effort, fewer and calmer breaths.
Slide the widget from low to high tolerance and watch the same pace turn from ragged breathing into something controlled. That shift is the whole point — same engine, calmer breathing. Here is how to build it:
- CO₂ tables, dry, 3–4× a week. Fixed comfortable holds with shrinking rests train exactly the CO₂ signal that shows up as early air hunger on a run. Build yours from your current max with the CO₂ tables generator.
- Apnea walks as a movement bridge. Holds while walking sit between a static table and a run — a low-intensity way to meet air hunger while your body is actually moving. Start with the apnea walk protocol.
- Nasal easy runs. Keep your recovery and base runs at a pace you can hold through the nose. If you are forced to open your mouth, you are running too hard for an easy day — which is useful pacing feedback in itself.
- Mouth open at intensity. On tempo, threshold and intervals, breathe however moves the most air. The efficiency you built at easy pace carries over; the ceiling at max effort is real and physiological.
Two weeks of consistent dry CO₂ work is enough to feel the early air hunger arrive later and quieter. That is the win — not a new VO₂max, but a pace that stops feeling like a fight.
Safety for runners
Never do breath holds while running, and never in or near water — a blackout on the move is far more dangerous than one seated. Keep all hold work dry and still: sitting or lying down. Stop any drill at the first sign of dizziness, tingling or tunnel vision. And never hyperventilate before a hold or a run to “feel fresher” — it silences the CO₂ alarm without adding oxygen and can drop you without warning.
Sources
- Recreational-runner breathwork trial (2025). Sports 13(2):31. DOI 10.3390/sports13020031
- Mapelli, M. et al. (2025). PLOS One 20(7):e0326661. DOI 10.1371/journal.pone.0326661
- Eser, P. et al. (2024). Frontiers in Physiology 15:1380562. DOI 10.3389/fphys.2024.1380562
Apnea Trainer is a breath-hold training app for iPhone and Apple Watch. It guides you through timed breathing cycles, builds progressive tables around your personal bests, and runs entirely on your wrist — live heart rate and haptic cues for every phase.
Keep reading
Apnea Walks: The Dry CO₂ Training You Can Do Anywhere
Movement makes CO₂ faster. Apnea walks turn that into the most time-efficient dry tolerance session there is — with a configurable interval timer.
CO₂ Tables Explained: The Science of Training Your Urge to Breathe
The urge to breathe is a CO₂ alarm, not an oxygen alarm. Here is how CO₂ tables train that alarm — and how to build one from your current max.