Muscles of Breathing
Updated: Dec 17, 2022
This past year one of the most influential books I read was “Breath” by James Nestor. I’ve been pretty fascinated with Anatomy for quite a while now, and particularly as a Yoga teacher I’ve been fascinated with how the way we breath can have such a drastic effect on the way we feel in our body, mind, and overall energy and vitality. I’ve decided to share a few posts focusing on the various muscles we use when we breathe to bring a sense of mindfulness and awareness to this vital aspect of living. I’ll start with the diaphragm, which is the most primary muscle used for breathing.
The diaphragm is a fascinating, yet often not well understood muscle in the body. It is the most primary muscle for breathing. It attaches to the base of the sternum, the lower ribs, and the lumbar vertebrae of the spine. When it's in its relaxed state it's shaped like a dome inside the thoracic cavity. When you inhale, you are contracting this muscle (whether voluntarily or not) which flattens the shape of the muscle as it expands the thoracic cavity creating negative pressure to draw air down into the lungs.
As James Nestor described in his book ‘Breath”, it’s incredibly common that people don’t actually take full advantage of this muscle and often don’t take steps to develop it. If you take a moment to notice how people around you breathe (or notice your own breath), you may find chest breathing is much more common than belly breathing, where the diaphragm is moving through its entire functional range.
Did you know that the nerves that innervate near the lower region of the lungs are responsible for the ‘rest and repair’ functions of the body, whereas the nerves that innervate near the upper region of the lungs are responsible for ‘fight and flight’ functions? James Nestor cited a research study which concluded that lung capacity was the single biggest predictor of life expectancy! Improving the functional range of the diaphragm can not only help to improve lung capacity, but also create a sense of calm and wellbeing throughout our nervous system.
In a Yoga practice, there is a technique for belly breathing called Dirgha Breath, or Diaphragmatic Breathing, which creates focused awareness on using the muscle of the diaphragm. It’s a three part breath that you can practice on your own at any time (a breath practice is incredibly personal and also private - no one will even know you are doing it). To practice Dirgha breath find a comfortable seat or lay on your back, and as you inhale slowly through your nose focus on expanding the belly first, followed by the ribs, followed by the chest (see if you can isolate the expansion in each area), and the exhale follows in the opposite progression, allowing the chest to fall, the ribcage to contract, and the belly to soften.
“A typical adult engages as little as 10 percent of the range of the diaphragm when breathing, which overburdens the heart, elevates, blood pressure, and causes a rash of circulatory problems” - This is a passage from James Nestor’s book Breath. Now imagine the effect of expanding the capacity of your diaphragm to 50 or 70 percent and how that would impact cardiovascular stress, pulmonary efficiency, and your mood.
While the diaphragm is the most primary muscle for breathing, it would be nearly impossible to breath properly without your other thoracic muscles. When you take a nice full, deep inhale the diaphragm contracts to create low pressure in the thoracic cavity for air to flow in, and another muscle group that is essential for this process to work properly are the Intercostals - specifically the External Intercostals.
You have 11 pairs of external intercostal muscles that are attached between each of your ribs. Each muscle elevates the rib below it when it contracts as you inhale, which has the effect of elevating and expanding the entire rib cage when the muscles are activated in harmony.
If what James Nestor said is true about the typical adult is using only 10% of the capacity of the diaphragm, this shallow breathing would also indicate that the intercostals are likely not being used as efficiently as they could to create an environment for more effortless breathing.
There’s a principle that when muscles don’t move, they become stiff. You can keep the intercostals moving by breathing deeper, as well as by moving your spine in all six directions - through flexion/extension (forward folds and heart lifting), lateral flexion/extension (side bends), and twisting (both directions) on a daily basis whether in a Yoga class or through some simple self-guided movements.
Sternocleidomastoid and Scalenes
Up to this point I’ve covered the diaphragm and intercostal muscles which are the muscles used for calm and relaxed breathing. As a quick recap, the contraction of those muscles draws air in and allows the ribcage to expand when you inhale. From a muscular perspective your exhale can be done completely passively without any muscles being engaged. In other words, the diaphragm and ribs can return to their natural shape on their own, which expels the air on your exhale.
I purposely covered those first two muscles because they are what you use for calm, relaxed breathing, whereas when you breathe with more force, such as during exercise, stress, or with intentionally deep inhales, additional muscles start to get involved.
The Sternocleidomastoid (SCM) and Scalenes might not be the first muscles you think of when you think of breathing because the primary function of these muscles is to move the head and neck through flexion, lateral flexion, and rotation; however since these muscles attach to your sternum, collar bone, and the top of your first two ribs, they are also responsible for elevating the ribcage when inhaling deeply.
A couple of my favorite stretches target the SCM’s and Scalenes. You can do these from any comfortable seat. I recommend elevating the hips off the floor by sitting on a block or towel. To start, clasp your hands behind your back and interlace your fingers. As you squeeze your hands together, draw your shoulders down and back. Next, turn your gaze up toward the ceiling, and press your chin outward. To add on, bring your lower lip over your upper lip. Hold for as long as feels good and release.
For another stretch to target your Scalenes and SCM (and upper trapezius), come back into a neutral seated position and place the back of your left hand (or left forearm) across your low back. Sit up tall, and draw your left shoulder blade down. Next, while keeping your gaze straight ahead, gently invite your right ear toward your right shoulder. You can add more to this stretch by placing your right hand over the top of your head and applying a bit of pressure. From this position you can change the stretch by rotating your gaze slightly up and down. Repeat on both sides.
Pectoralis Major and Minor
Upper Cross Syndrome (UCS) is a condition that seems to be becoming more and more common in a world where many of us are spending hours either sitting in front of a computer, looking down at our phones, driving, and generally having poor posture for long periods of time. It’s a condition that causes the shoulders to protract and round forward, the curve in the thoracic region of the spine to become exaggerated, and the head to be carried forward. The muscular imbalance associated with this creates structural posture change, which can lead to a host of issues in the body, including breathing.
The Pectoralis Major and Minor are another muscle group which may not be the first thing you think as breathing muscles. Their primary function is to flex the arm (in front of you), adduct the arm (toward your centerline), and to protract the shoulder blade forward. Since these muscles originate along the sternum, the collar bone, and your 3rd through 5th ribs, they are also accessory muscles for deep inhales, because they help to elevate the ribs and expand the thoracic cavity. However, as these muscles become tight and shortened, such as with UCS, space is decreased in the thoracic cavity and they effectively inhibit the ability for the ribcage to expand when you breathe in, making it more difficult to breathe.
To help with this posture, it’s a great idea to strengthen muscles around your shoulders like your rhomboids which draw the shoulders back, and paraspinal muscles which help you sit/stand up taller. Otherwise, once the Pectoralis muscles become shortened and tight, remedial massage therapists can use functional release techniques to help, or you can get into your own stretching regime.
The stretch the Pectoralis Major, lay face down on the floor. Extend your right arm directly out beside you with your palm facing down. Use your left hand to press into the floor to roll onto your right side. To transfer this stretch to the Pectoralis Minor, come back to lay face down with the arm out beside you. Bend your elbow to 90 degrees, and roll back onto your right side. Hold each stretch for at least 30 seconds and repeat on both sides.
Serratus Anterior & Posterior
There are numerous accessory breathing muscles, and what I am including here is by no means an exhaustive list. An accessory breathing muscle is any muscle which affects the intrapleural pressure that draws air in and out of the lungs. Some muscles help to lift the ribs on an inhale, and other muscles help with the exhale. Arguably, any muscle that becomes tight, weak, or restrictive to the natural breathing process could be considered a breathing muscle if those conditions are present.
The main function of the Serratus Anterior is to help with protracting your shoulder blades forward since this muscle is attached to the scapula and the first 9 ribs, however when you hold your shoulder blades in place, it functions to elevate the ribs when you breathe in.
As I mentioned earlier with Upper Cross Syndrome being such a common condition these days with shoulders rounded forward from typing, driving, sitting, etc, the Serratus Anterior can actually become quite weak due to other muscles and posture changes affecting the position of the shoulder. Since the muscle cannot move through its normal functional range, this causes the muscle to atrophy, especially at its end range.
To strengthen Serratus Anterior, come to hands and knees. Allow the chest to sag down between the shoulders toward the floor and shoulder blades to protrude from your back, and then press into your hands and imagine separating your shoulder blades apart as you press. Lower the chest back down slowly, and repeat.
Most people are more familiar with Serratus Anterior than the Serratus Posterior muscles. , The Serratus Posterior Superior is also responsible for elevating ribs on an inhale, and the Serratus Posterior Inferior helps with depressing the ribs with a forced exhale. This brings us to muscles that help with exhaling.
Up to this point I’ve mostly discussed muscles involved with inhalation. As I mentioned earlier, for inhalation it requires at least the engagement of the diaphragm and intercostals for calm, passive breathing. Exhalation can happen without the engagement of any muscles at all. With that said, any forced or labored breathing requires additional accessory muscles to get involved, which is also true for exhalation.
Since the group of abdominal muscles including the Internal and External Obliques, Rectus Abdominis, and Transverse Abdominis attach to the pelvis, ribs and sternum, as those muscles engage to flex, twist, and laterally flex your trunk, those actions decrease volume in the thoracic cavity which increase the pressure within your abdominal cavity. This in turn essentially pushes the diaphragm up, and helps to push the air out. Perhaps the biggest actor in this process is the Rectus Abdominis (the six pack) which pulls the ribs down on active exhalation. Arguably when any of the abdominal muscles move your trunk, they affect the intra-abdominal pressure that directly affects the intrapleural pressure which controls breathing.
From a Yoga perspective, you probably hear Yoga teachers say “soften your belly” while you breathe, which is promoting a calm, relaxed, diaphragmatic breathing process. This is generally a good thing (how you breathe can be a reflection of how you think and how you feel). However, there are specific breathing techniques such as Uddiyana Bhandha which function to stretch and strengthen the diaphragm, as well as the pelvic floor. Yogis have been using it for thousands of years, and in the past few decades “Hypopressive Breathing” and “Low Pressure Fitness'' have caught on with research backing up the effects of respiratory muscle strengthening, diaphragmatic mobility, and improving pelvic floor health. Definitely worth a quick search if you’re not familiar with it.
The muscles I wrote about here are by no means a comprehensive list of all of the muscles involved in breathing, but even with the ones I did cover it’s pretty incredible how this symphony of coordination is often controlled without us having to even think about it. Our body allows us to breathe involuntarily, however we also have the ability to breathe with intention. We can breathe in ways to calm us down or energize ourselves. We can hold our breath in and hold our breath out. We can breathe deeply or shallowly. We can be mindful of our breathing or just let it be automatic.
If I took one thing away from the book Breath by James Nestor, is that having a mindful breath practice is something that can promote health and wellbeing in pretty much every way imaginable - physically, mentally, emotionally, and energetically. The research he found in the study that concluded how lung capacity is the number one factor in predicting life expectancy is also something that stuck with me and how a breathing practice that promotes pulmonary fitness can change both how long we live, and the way we feel each day while we are alive.
About the Author:
Jason has been teaching Yoga in Wollongong since 2019 and began teaching Yoga after his teacher training at Yoga Six in San Diego California in 2017. He has since completed a Diploma of Remedial Massage Therapy and is passionate about creating and facilitating space for growth, transformation, and overall wellbeing. He primarily teaches Vinyasa Yoga, and offers Massage treatments designed for Yogis to embody their breath, improve posture, and soothe the nervious system.