Which muscles make us breathe?
Breathing is mostly the diaphragm's work: this dome under the lungs moves down about 2.3 cm (0.9 in) at rest and 5.5 cm (2.2 in) in a deep breath (Kabil, 2022). The muscles between the ribs lift the rib cage; during exercise, those of the neck and belly join in.
Simplified diagram for a healthy adult. Muscle activity in relative levels. Dashed curves are estimates.
Which muscles make us breathe?
The lungs have no muscle: the muscles around them are what make them expand. The diaphragm, a dome under the lungs, moves down and does most of the work at rest. The muscles between the ribs lift the rib cage. During exercise, the neck and belly muscles join in. Tap a muscle, on the drawing or in the list, to see it alone.
Sources: role of the muscles (De Troyer and Boriek, Compr Physiol, 2011). Diaphragm movement: 2.3 cm at rest and 5.5 cm in deep breathing, on average in 757 adults (Kabil, Multidiscip Respir Med, 2022). Phrenic nerve (StatPearls). Hiccups (Kahrilas and Shi, Gut, 1997). Resting rate: 12 to 18 breaths per minute (MedlinePlus). Liters of air, and breathing rate during exercise: textbook orders of magnitude (to be checked).
Keyboard: 1 to 4 the situation, Space pause, L slow motion, Esc all the muscles.
Frequently asked questions about breathing and the diaphragm
Do the lungs have muscles?
The lungs have no muscle: the diaphragm and the muscles between the ribs make them expand by enlarging the rib cage. Two thin layers, the pleura, with a little fluid between them, hold the lungs against the chest wall: when the rib cage gets bigger, they follow (De Troyer and Boriek, 2011). During exercise, muscles of the neck and belly help out.
What does the diaphragm do?
The diaphragm is the main breathing muscle: this dome under the lungs flattens and moves down when it contracts, which draws air in. Measured by ultrasound in 757 healthy adults, it moved down 2.3 cm (0.9 in) on average at rest and 5.5 cm (2.2 in) during a deep breath (Kabil, 2022). It is controlled by the phrenic nerve, which starts in the neck, and it separates the chest from the belly.
How many breaths per minute is normal?
At rest, an adult usually breathes 12 to 18 times a minute (MedlinePlus). At 14 breaths a minute, that comes to about 20,000 breaths a day (our calculation: 14 × 1,440 minutes). The rate goes up with exercise, fever or strong emotion. Fast breathing at rest that does not settle calls for medical advice.
How do you do belly breathing?
Belly breathing means letting the diaphragm do the work: as it moves down, it pushes the organs down, and the belly gently rises as you breathe in. To feel it, a hand placed on the belly should rise more than one placed on the chest. This is the normal way to breathe at rest. Slowed to about 6 breaths a minute, it helps you calm down, according to a review of 15 studies (Zaccaro, 2018).
Why do we get hiccups?
A hiccup is a sudden, involuntary contraction of the diaphragm, followed right away by the closing of the glottis, at the back of the throat, which makes the "hic" sound (Kahrilas and Shi, 1997). It often follows a big meal, a fizzy drink or strong emotion, and usually goes away on its own. Beyond 48 hours, it is called persistent hiccups and calls for medical advice (StatPearls).
How can you practice breathing slowly?
You can follow a guided rhythm: breathing in for 5 seconds, then out for 5 seconds, gives 6 breaths per minute (our calculation: 60 ÷ 10). Free guided exercise, no sign-up (box breathing, 4-7-8, coherent breathing), on our sister site ChakraDuo.
True or false?
At rest, you need muscles to breathe out.
False. At rest, breathing out is passive: the elastic lungs empty on their own when the diaphragm relaxes. The abs only push air out during exercise (De Troyer and Boriek, 2011).
Your rib cage doesn't move when you breathe.
False. The intercostal muscles lift the ribs and spread them apart, a bit like lifting the handle of a bucket (De Troyer and Boriek, 2011).
Neck muscles help you breathe.
True. During a deep breath or exercise, the scalenes pull the first 2 ribs up and the sternocleidomastoid muscles lift the breastbone (StatPearls).
This page as text
The same information as the charts, to read without animation: for each chart, the values at the main moments, then the notes with their level of evidence.
Calm breathing, at rest
At rest, we breathe 12 to 18 times a minute without thinking about it. Only breathing in takes effort: the diaphragm moves down, the ribs rise a little, and air comes in. Breathing out happens on its own.
| Seconds | Air in the lungs | Diaphragm (dotted) | Muscles between the ribs (external intercostals) (dotted) | What happens |
|---|---|---|---|---|
| 0 s | 14 | 0 | 0 | breathing in |
| 2 s | 22 | 0 | 0 | breathing out |
| 4 s | 14 | 0 | 0 | breathing in |
| 6 s | 22 | 0 | 0 | breathing out |
| 8 s | 14 | 0 | 0 | breathing in |
| 10 s | 22 | 0 | 0 | breathing out |
| 12 s | 14 | 0 | 0 | breathing out |
Key points
- The lungs follow the rib cage (Throughout, Shown in humans)
The lungs have no muscle. Two thin layers, the pleura, with a little fluid between them, hold them against the chest wall: when the rib cage gets bigger, they get bigger with it. Source: De Troyer and Boriek, « Mechanics of the respiratory muscles », Compr Physiol, 2011 - The diaphragm moves down about 2 cm (0.8 in) (From 0 to 1.6 s, Shown in humans)
Measured by ultrasound in 757 healthy adults: 2.3 cm (0.9 in) on average at rest. Source: Kabil et al., « Diaphragmatic excursion by ultrasound: reference values for the normal population », Multidiscip Respir Med, 2022 - The ribs rise like a bucket handle (From 0.3 to 1.6 s, Shown in humans)
The muscles between the ribs lift them and spread them apart: the rib cage widens. Source: De Troyer and Boriek, « Mechanics of the respiratory muscles », Compr Physiol, 2011 - Breathing out is passive (From 1.6 to 4 s, Shown in humans)
The muscles relax, and the lungs, which are elastic, go back to their size like a balloon letting out air. Source: StatPearls, « Anatomy, Thorax, Phrenic Nerves »
A deep breath
To fill the lungs all the way, the diaphragm moves much lower, and the neck muscles lift the top of the rib cage.
| Seconds | Air in the lungs | Diaphragm (dotted) | Muscles between the ribs (dotted) | Neck muscles (scalenes, sternocleidomastoids) (dotted) | What happens |
|---|---|---|---|---|---|
| 0 s | 14 | 0 | 0 | 0 | breathing in |
| 2 s | 57 | 80 | 67 | 27 | breathing in |
| 4 s | 100 | 45 | 35 | 40 | pause, lungs full |
| 6 s | 47 | 0 | 0 | 0 | breathing out |
| 8 s | 20 | 0 | 0 | 0 | breathing out |
| 10 s | 14 | 0 | 0 | 0 | breathing in |
| 12 s | 57 | 80 | 67 | 27 | breathing in |
Key points
- The diaphragm moves down 5 to 6 cm (2 to 2.4 in) (From 0 to 4 s, Shown in humans)
In deep breathing, it moved down 5.5 cm (2.2 in) on average in 757 healthy adults. Source: Kabil et al., « Diaphragmatic excursion by ultrasound: reference values for the normal population », Multidiscip Respir Med, 2022 - The neck pitches in (From 1.4 to 4.8 s, Shown in humans)
The scalenes pull the first two ribs upward; the sternocleidomastoids lift the breastbone. Source: StatPearls, « Anatomy, Head and Neck, Scalenus Muscle » - Up to 3 L more (From 2 to 4.8 s, Hypothesis)
A deep breath can bring in up to about 3 L of air more than a calm breath (textbook order of magnitude, to be checked). - The air comes out almost on its own (From 4.8 to 10 s, Shown in humans)
Even after a deep breath, breathing out stays largely passive: the lungs, which are elastic, empty by themselves. Source: De Troyer and Boriek, « Mechanics of the respiratory muscles », Compr Physiol, 2011
Breathing during exercise
During intense exercise, we breathe faster and harder. Breathing out becomes active: the belly muscles push the air out.
| Seconds | Air in the lungs | Diaphragm (dotted) | Neck muscles (dotted) | Abdominal muscles (dotted) | Internal intercostals (dotted) | What happens |
|---|---|---|---|---|---|---|
| 0 s | 6 | 0 | 0 | 0 | 0 | breathing in |
| 2 s | 46 | 83 | 54 | 0 | 0 | breathing in |
| 4 s | 69 | 0 | 0 | 29 | 24 | breathing out |
| 6 s | 33 | 0 | 0 | 84 | 69 | breathing out |
| 8 s | 6 | 0 | 0 | 0 | 0 | breathing out |
| 10 s | 46 | 83 | 54 | 0 | 0 | breathing in |
| 12 s | 69 | 0 | 0 | 29 | 24 | breathing out |
Key points
- Faster, harder (Throughout, Hypothesis)
During intense exercise, about 2 L of air with each breath and 35 to 50 breaths a minute (orders of magnitude, to be checked). - The abs blow the air out (From 0 to 4 s, Shown in humans)
They squeeze the belly: the organs push the diaphragm back up and drive the air out. Source: De Troyer and Boriek, « Mechanics of the respiratory muscles », Compr Physiol, 2011 - The internal intercostals lower the ribs (From 4 to 8 s, Shown in humans)
Crossing the external ones, they tighten the rib cage to empty the air faster. Source: De Troyer and Boriek, « Mechanics of the respiratory muscles », Compr Physiol, 2011 - The diaphragm starts from higher up (From 8 s, Shown in humans)
At the end of an active breath out, it rises above its resting place, which gives it more travel for the next breath in. Source: De Troyer and Boriek, « Mechanics of the respiratory muscles », Compr Physiol, 2011
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