Breathing: the movement you train least of all

We train our legs, our back, our heart. Then there is a muscle that works between twenty and twenty-five thousand times a day, without you ever thinking about it, and that almost nobody trains: the diaphragm. It is the main engine of breathing, and it is also one of the central pieces of the system that keeps you stable while you move.

This is not a topic for breathing gurus. It is exercise physiology, and it has measurable effects on how well you hold up on a climb and how quickly you recover.

It is not oxygen that makes you breathe

This is the part that surprises almost everyone. When you reach the top of a climb out of breath, the feeling is “I can’t get enough air”. In reality, under normal conditions and at low altitude, the blood leaving your lungs is already 96-98% saturated with oxygen, even while you are pushing hard. It is not oxygen you are short of.

What drives you to breathe is mainly carbon dioxide. The chemoreceptors — in the brainstem and in the arteries — are far more sensitive to a rise in CO2 and a change in pH than to a drop in oxygen. As the intensity goes up, you produce more CO2, and the body increases ventilation to clear it. Breathlessness is the response to that, not to a lack of oxygen.

This has a practical consequence: CO2 tolerance can be trained. And it is one of the reasons why, with the same engine, two people can perceive the same effort very differently.

Nose or mouth

At low and moderate intensity the nose is almost always the better choice: it filters, warms and humidifies the air, slows the flow and encourages a deeper, diaphragmatic breath. It also produces nitric oxide, which has a vasodilating effect on the pulmonary circulation.

Above a certain intensity, though, the nose becomes a bottleneck: the resistance to airflow is too high and the cost of breathing through it outweighs the benefit. That is where the mouth is needed, and sticking with the nose on principle is just a way of paying an unnecessary toll.

The rule I use with the people I coach is simple: nose in easy sessions and in the warm-up, mouth when the intensity calls for it. Anyone who cannot keep to nasal breathing even in base training usually just has an aerobic base to build — or a mechanical problem to have looked at by a specialist, and that is a distinction worth clearing up before insisting.

The diaphragm does more than breathe

The diaphragm is part of the system that generates intra-abdominal pressure: the one that, together with the pelvic floor and the abdominal wall, gives you a stable column through which to transfer force. When you breathe only with the upper chest — shoulders rising, neck working — that system loses efficiency, and the body compensates by stiffening something else.

That is why, in an assessment, I always look at how a person breathes at rest too, before loading them at all. A high, short breathing pattern is not a cosmetic detail: it changes how the trunk organises itself under load, and it is often one of the things to fix before adding weight to the bar.

When your breathing muscles steal from your legs

This is the part that convinces even the most sceptical. Above roughly 85% of maximal oxygen uptake, the work of the respiratory muscles comes to cost a significant share of all the oxygen you are consuming. And when those muscles fatigue, a reflex kicks in — the respiratory muscle metaboreflex — which increases peripheral vasoconstriction to redistribute blood towards the breathing muscles.

In plain terms: under intense, prolonged effort, a diaphragm in trouble takes blood flow away from your legs. It is not a feeling, it is a measurable redistribution. And it is why training the respiratory muscles makes sense above all for people who race long and hard, or who move at altitude, where the ventilation required is even higher.

How I train it, in practice

Nothing esoteric, four concrete things:

1. Nasal breathing in low-intensity sessions. It builds CO2 tolerance and brings the breath back down, onto the diaphragm. At first it is uncomfortable: that is normal, and it is exactly the point.
2. Specific work on the inspiratory muscles, with an adjustable-resistance breathing trainer. A few sets, almost every day, like any other muscle you want to make more resistant to fatigue.
3. Thoracic and rib mobility. A stiff ribcage limits the diaphragm’s range no matter how strong it is. The quickest gains often come from here.
4. Long exhales for recovery. Exhales longer than the inhale, for a few minutes after a hard session or before sleep: it is the most direct way to shift the balance towards the parasympathetic system, the one that governs recovery. I wrote about why that matters so much in the article on recovery, sleep and HRV.

An honest limit

If breathlessness comes at rest, at night, or out of all proportion to the effort, it is not a breathing-technique problem: it is something to have a doctor look at before any training. Asthma, chronic rhinitis, a deviated septum and heart problems need a diagnosis, not a breathing exercise. My work starts afterwards, and alongside — never instead.

That said: if you breathe well, everything else in your training works better. It is the piece with the best ratio of effort to return that I know.