How to use your breath to control your effort

That works because breathing is two things at once. Most of the time you never think about it. The brainstem, at the base of your brain, runs it automatically, day and night, faster when you work and slower when you rest. But you can take it over whenever you like. You can hold your breath, slow it down, or move it from your mouth to your nose. You cannot decide how fast your heart beats, but you can decide how you breathe.

That is what makes breath more than a sign of how hard you are working. Left to run on its own, it follows the effort. Taken over, it sets the effort. And air has only two ways in, the nose and the mouth. Which one you use for the in-breath, and which for the out-breath, gives you a way of breathing for each effort you train at, from the gentlest to the hardest. Nose or mouth is a choice you can make on every breath, and it is the only one you need to make. So while you move there is just one thing to think about, and that is how you breathe.

The nose is the narrow way in, and the narrowness is the point. Breathing in and out through it alone, you can only move so much air. Speed up past that and within a minute or two you run short of air, and you have to slow down or open your mouth. Keep it shut and you cannot go too hard. So nose in and nose out keeps you at base, the effort you could hold for hours.

The limit comes early, and most people open their mouth when they reach it without ever deciding to. In 1980, researchers had thirty adults ride harder and harder on a bike while they measured the air passing through the nose and the mouth separately. Twenty of them began to breathe through the mouth as well at a moderate effort, far below their hardest. By then, breathing through the nose alone had become hard work. At base you keep the mouth closed on purpose, and the effort stays where you want it.

Some days you train above base. When you need to go faster than the nose allows, you open your mouth, but only on the way out. You still breathe in through your nose. This is threshold, the hardest effort you can hold for about twenty minutes, and the in-breath stays in the nose because of what the nose does for it.

First, the nose helps you breathe with your diaphragm, the wide sheet of muscle under your lungs that does most of the work of breathing. When researchers scanned the diaphragms of young adults, those who habitually breathed through their mouth had diaphragms that moved less with each breath than those who breathed through their nose.

Second, the nose adds something to the air. The sinuses, the hollow spaces in the bones around your nose, make a gas called nitric oxide. A breath in through the nose carries it down into your lungs, where it widens the small blood vessels so that more blood meets the air and you take more oxygen out of each breath. In Stockholm, Jon Lundberg and his colleagues measured the oxygen in healthy people's blood through their skin, and it was about a tenth higher while they breathed through the nose than while they breathed through the mouth.

The out-breath goes through the mouth for a simpler reason. The mouth is the bigger opening, so the air leaves faster and you can take the next breath sooner. At threshold you need more breaths each minute than the nose can carry in both directions, so the out-breath gets the wide opening and the in-breath stays where it does the most good.

Above threshold, the aim changes. VO₂max is the most oxygen you can take in and use, and you train it with hard efforts that last a few minutes. However good the air the nose brings, it is now too narrow for how much you need. The only thing that matters is how much air you can move, so you use the biggest opening you have. You breathe in and out through your mouth, as hard as you can.

It feels like gasping, and the gasping is the training. It works the muscles that pull the air in and push it out, and it builds your capacity to take in oxygen. This is the last effort where how you breathe is the thing to think about.

Go faster still and the breath stops mattering. A sprint is the one effort where you can stop thinking about it. For those few seconds at full speed, your muscles run mostly on the anaerobic system, the energy that does not need oxygen. Breathing harder cannot make that energy come faster, and how you breathe makes little difference to how fast you go. So you do not think about it. You just go, and when you stop, breathing runs on its own again.

So the whole ladder comes down to one thing you can change on any breath. Breathing in and out through your nose keeps you at base. Opening your mouth on the way out lets you rise to threshold. Opening it both ways, as wide as it goes, takes you to VO₂max. And in a sprint you leave your breathing alone and just go.

You need no watch or screen for any of this, and it works the same on a run, a ride or a long climb on foot. Most of the time you let breathing run on its own, and it tells you how hard you are working. When you want a different effort, you take it over and change how you breathe, and your effort changes with it.

• Niinimaa et al. 1980. Respiration Physiology 42:61-71. The switching point from nasal to oronasal breathing.
• Trevisan et al. 2015. Journal of Electromyography and Kinesiology 25:463-468. Diaphragm movement in nasal and mouth-breathing adults.
• Lundberg et al. 1996. Acta Physiologica Scandinavica 158:343-347. Inhalation of nasally derived nitric oxide modulates pulmonary function in humans.