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Chest breathing and the intercostals: why a full breath starts with the belly

The order of a full breath is not arbitrary. This covers the two separate ways ribs move, why the diaphragm has to go first, why flexibility matters more than capacity, and a reason most people never consider — training the ribcage is not only about taking in more air, it is about being able to compress gently at depth.

Safety first. This is about breathing mechanics on land, not breath-hold training. Any breath-hold in water needs a buddy watching you — shallow water blackout gives no warning, and practising alone is the most dangerous thing in freediving. Do not push breathing drills to the point of dizziness either: dizziness means hyperventilation, which is not "training deeper", it is blowing off carbon dioxide. Later on this covers packing, which is an advanced technique with documented injuries; the risks are written out alongside it.

In freediving you often hear the recommended order for a full breath: diaphragm first (belly), then chest (intercostals). This maximises the volume you take in.

What rarely gets explained is why that order, and what "chest breathing" actually is inside your body. This is about both.

Ribs move in two different ways

Here is an analogy I like to use when teaching: the intercostals act on your ribs like the two handles of a bucket. Pull the handles up and out, and the bucket rises with them — that is how the ribs swing outward.

I later found out this analogy has a proper anatomical name: bucket handle movement. And it is only one of two.

Ribs move in two distinct ways, in two different regions:

(Textbooks divide the upper and lower groups slightly differently, but the two directions of movement are consistent.)

The joints of the upper ribs have a mostly side-to-side axis, so those ribs can only arc forward, like the handle of an old water pump. The joints of the lower ribs have a mostly front-to-back axis, so those ribs can only swing out to the sides, like a bucket handle.

This is why "chest breathing" is not one single movement. Your chest expands front-to-back and side-to-side at the same time, driven by different sections of the ribcage. Some people only feel the chest lift forward when they inhale — that usually means the lateral expansion of the lower ribs has not woken up yet, which is very normal early on.

Why the diaphragm goes first

This is anatomy, not habit.

First, the lower half of the lung is where the work happens. Standing upright, gravity makes ventilation at the base roughly 50% greater than at the apex, and most gas exchange during normal quiet breathing occurs in the lower lobes. That is exactly the region the diaphragm fills as it descends. Fill the bottom first, then stack the intercostals on top, and the total is larger.

Second, the reverse order gets in its own way. If you expand the ribcage first and lift the ribs to their highest position, the diaphragm then has to descend into an abdomen that has no room left to give. Let the diaphragm drop first, let the belly rise, and the ribcage is still empty and free to expand afterwards.

Third, and most easily missed — this is about relaxation. Diaphragmatic breathing uses very few muscles, like the way you breathe falling asleep, where only the belly moves. Chest breathing recruits far more. If your whole breathe-up is chest-driven, you arrive at the dive already tenser than you need to be. So the real sequence is: stay on the diaphragm for the breathe-up, and add the chest only on the final breath.

So should you lift your shoulders?

Mainstream teaching adds a third stage: after the intercostals, lift the shoulders a little to open the very top of the lungs.

My view is that you do not have to.

If, in the moment, lifting your shoulders at the end genuinely helps you take in more air, then there is nothing wrong with it. But there is no point lifting for the sake of lifting.

The reason is that some people, when they lift their shoulders, end up recruiting the muscles of the lower back as well. That is not what we want — the extra energy you spend cancels out the small amount of extra air you gained.

There is a principle running underneath all of this:

So it is a balance. Lifting the shoulders is not a compulsory step; it is an option you take if it helps you.

None of this is a slogan

While we are here, something more important than the technique itself.

None of this is a slogan. You do not need to treat it as a doctrine where step one through step five must all be completed for it to count.

It is actually a very natural thing. Once you understand the safety framework, a lot of it is yours to adapt.

I think of it as a conversation with yourself — noticing which parts help you, which parts actually make you tenser, and keeping what works. That process is itself part of the practice.

So what does it look like to breathe with the intercostals "only"?

That is what the video is doing.

In it I isolate chest breathing and push it as far as it goes, and in the last section I consciously contract and relax the intercostals quickly while holding my breath. You can see the ribs moving while the belly stays essentially still.

I filmed it because plenty of people have heard the phrase "chest breathing" without ever seeing what it looks like on its own. Once you know what the movement is supposed to feel like, you can check yourself.

A very common way to fool yourself

One thing to watch for in practice: do not use the side muscles of your abdomen to fake the same effect.

The reason is this: the abdominal wall muscles — the obliques and transversus — are expiratory muscles, not inspiratory ones. When they contract they do three things: draw the abdominal wall inward, raise intra-abdominal pressure and push the diaphragm upward into the chest, and pull the ribcage downward.

Not one of those makes the chest bigger. All three make it smaller. So if you recruit them during the inhale, you are working against your own inhale.

The check is simple: put your hands on the sides of your lower ribs, roughly a palm's width below the armpit. On the inhale you want to feel bone pushing outward, not soft abdominal wall bulging. Bone moving is real expansion.

Why flexibility matters more than capacity

This is the part I most wanted to write down.

First, to be clear: capacity does differ from person to person by birth, and I am not going to pretend otherwise. Height, build and skeletal frame are what they are. A study of 14 world-championship freedivers found vital capacity did correlate with competition score — the top three averaged 7.9 litres, the bottom three 6.7.

But flexibility is something you can train, and training it directly widens how far your chest expands when you breathe:

• Lifting the intercostals — so both rib movements are actually available to you
• Stretching the diaphragm — so it can descend further
• Some yoga postures — side bends, twists and chest openers all work the same structures

These are not separate projects. They all address one thing.

One warning here: stretching on empty lungs carries more risk for beginners. Stretching with the air emptied out of your lungs can make you faint. So when you do this kind of work, pay attention to what is around you — nothing sharp nearby — and do it with someone supervising if you can.

So when I say "flexibility matters more than capacity", what I am really talking about is a mindset: the capacity you were born with can be worked on through effort and stretching. Where you start is not where you end. Rather than agonising over whose lungs are naturally bigger — which you cannot change — put the effort into the part that actually responds to you.

And this is more than encouragement. Long-term studies of competitive freedivers show their lung volumes are larger than controls, above predicted values, and continue to increase over years of training. Train flexibility, and capacity grows with it.

At depth, the ribcage also has to be crushable

Flexibility has a second reason, and this one is directly about safety.

As you descend, the gas in your lungs compresses as pressure rises. At some depth, lung volume approaches your residual volume — the air left after a full forced exhale, roughly 20–25% of total lung capacity in an untrained person. Below that, the chest itself has to keep deforming, or negative pressure develops.

That is where flexibility of the ribcage and diaphragm becomes the deciding factor. There is a point made in freediving medicine that I find persuasive: for deep diving, ribcage and diaphragm flexibility matters more than the residual-volume number itself — a small RV does not prove your chest deforms well passively, whereas good flexibility helps either way.

Likewise, among the factors that prevent lung squeeze, "a flexible ribcage and diaphragm" sits near the top of the list, alongside good posture, no sudden movements, and conservative progression.

So training the intercostals is, in the short term, about filling that last breath. In the long term it is about teaching the ribcage to deform gently. Same muscles, two completely different purposes.

What about packing?

Packing — properly called glossopharyngeal insufflation — is an advanced breathing technique: with your chest already under considerable pressure, you use your mouth and throat together to push still more air down into the lungs.

My view is that packing is actually not easy to train.

The reason is that packing requires opening the glottis. And at the moment the glottis opens, your chest is already under substantial positive pressure, so air can easily escape outward instead. A lot of people practising packing are not efficient at it at all — more air may be coming out than going in, or they are making the shape of packing with their mouth while the air is not actually going down.

Beyond the efficiency problem, packing has a documented injury record, and it seems right to set that out too:

• Packing blackout — people have lost consciousness in the first seconds of the breath-hold, before the dive even began, because the rise in intrathoracic pressure reduces cerebral blood flow
• Falling blood pressure and cardiac output — packing causes a prompt drop in arterial blood pressure and a marked decrease in cardiac output
• Raised heart rate — which works directly against the oxygen conservation you were after
• Pulmonary barotrauma — pneumothorax, pneumomediastinum and lung bleeding have all been reported in connection with packing

To be fair to it: packing does raise the ratio of total lung capacity to residual volume, which in theory lowers the risk of lung squeeze. So it is not a purely harmful technique — it is a technique that is steep on both sides.

Either way, my position is this: packing is something to consider when you actually need it, not somewhere a beginner should be spending time.

An honest caveat

To be clear: the intercostals cannot work in complete isolation.

In the video I use them as exclusively as I can, but the diaphragm is certainly still contributing, and that mechanism cannot be removed entirely. So the demonstration is "as isolated as possible", not "fully isolated".

I mention this because technical information about freediving online is often presented too cleanly, too absolutely. Bodies do not work that way.

Recap

• Ribs move two ways: upper ribs like a pump handle (lifting forward, expanding front-to-back), lower ribs like a bucket handle (swinging out sideways, expanding side-to-side)
• A full breath goes diaphragm first, then intercostals, for three reasons: ventilation at the lung base is about 50% greater than at the apex, the reverse order blocks itself, and diaphragmatic breathing is more relaxed
• Use the diaphragm for the breathe-up; save the chest for the final breath
• Lifting the shoulders is optional. Do it if it helps, but not for its own sake — some people recruit the lower back doing it, and the extra cost cancels the extra air
• None of this is a slogan or a fixed five-step sequence. Once you understand the safety framework, much of it is yours to adapt
• The common self-deception is faking expansion with the abdominal wall. The obliques and transversus are expiratory muscles — they push the diaphragm up and pull the ribs down. Feel your lower ribs; you want bone moving
• Stretching on empty lungs can make you faint: keep sharp objects away and have someone supervising
• "Flexibility over capacity" is a mindset: capacity does differ by birth and does correlate with performance (world-championship study), but that gap can be worked on through stretching — and capacity grows along with flexibility anyway
• Flexibility's second reason is safety: at depth the ribcage has to compress gently, which is one of the factors that prevents lung squeeze
• Packing is advanced, hard to do efficiently (positive pressure escapes when the glottis opens), and carries documented packing blackout, blood-pressure and barotrauma risks. Consider it when you need it
• The intercostals cannot be fully separated from the diaphragm; the demonstration is "as isolated as possible"

References

1. Pump handle and bucket handle rib motion, the diameters each expands, and the rib segments involved — StatPearls, Anatomy, Thorax, Wall Movements (NCBI Bookshelf)
2. Segmented order of a full breath (diaphragm → intercostals → shoulders) — DeeperBlue, Breathing for Freediving
3. Ventilation at the lung base is roughly 50% greater than at the apex when upright; most gas exchange in quiet breathing occurs in the lower lobes — StatPearls, Physiology, Pulmonary Ventilation and Perfusion (NCBI Bookshelf)
4. Residual volume is roughly 20–25% of total lung capacity, and trained freedivers can reach 20% or below — Molchanovs, Discover How Lung Volume Impacts Your Freediving
5. Competitive freedivers' lung volumes exceed controls and predicted values; a three-year follow-up showed increased ventilatory volumes attributed to repeated GI training — Evidence of respiratory system remodelling in a competitive freediver, European Respiratory Journal
6. Among 14 world-championship freedivers, vital capacity correlated with competition score (top three averaged 7.9 L, bottom three 6.7 L) — Size Matters: Spleen and Lung Volumes Predict Performance in Human Apneic Divers, Frontiers in Physiology (2012)
7. "For deep dives, the flexibility of the diaphragm and the ribcage is more important than RV" — Deep Med, RV and Exhale diving
8. Lung squeeze prevention factors include a flexible ribcage and diaphragm, good posture, avoiding jerky movements, and conservative progression — Molchanovs, 6 Tips to Avoid Lung Squeezes in Freediving
9. Definition of packing (glossopharyngeal insufflation) and its effect of raising the total-lung-capacity to residual-volume ratio, mitigating lung squeeze risk — DeeperBlue, Risks Associated With Lung Packing In Freediving
10. Packing blackout: loss of consciousness in the first seconds of apnea linked to reduced cerebral blood flow; packing causes a prompt fall in arterial blood pressure and cardiac output — Glossopharyngeal Insufflation and Breath-Hold Diving: The More, the Worse?
11. Pneumothorax, pneumomediastinum and lung injury reported in connection with packing — Adverse Events in Competitive Freediving, German Journal of Sports Medicine (2024)
12. The abdominal wall muscles (rectus, internal and external obliques, transversus) are expiratory: contracting them raises intra-abdominal pressure, pushes the diaphragm cephalad, and pulls the ribcage downward — Johns Hopkins, Muscles of Respiration