How Your Most Important Muscle (the Diaphragm) Works

How Your Most Important Muscle (the Diaphragm) Works

Nick Heath, PhD Nick Heath, PhD
4 minute read

"The diaphragm…to a certain extent represents the sole skeletal muscle that is essential for life.
- Poole et al. (1997)

The diaphragm is our primary breathing muscle, the “sole skeletal muscle that is essential for life.” We use it over 20,000 times a day, contracting and relaxing it with each breath we take. But we should all probably be using it even more. Intuitively, we probably already knew this. We know that deep, diaphragmatic breathing is relaxing and that doing it more would benefit our health. But to really appreciate the power of this practice, we must first understand the diaphragm, the centerpiece of our breathing.

What is the Diaphragm?

The diaphragm is a thin, dome-like, and fascia-like muscle. Although it sustains life, it only accounts for less than 0.5% of your body weight. The word “diaphragm” literally means “something that divides” or “a barrier,” which is fitting because, anatomically, the diaphragm separates the chest cavity from the abdominal region. The diaphragm connects to your sternum, lower ribs, and spine. It extends in a 360-degree fashion, sitting right below your lungs and heart. To remember its intimate connection with these vital organs, author and yoga instructor Jill Miller has an ingenious way of putting it: “Thank you from the bottom of my heart, which is, of course, my diaphragm.” It is controlled by the phrenic nerve. When this nerve sends the message to “breathe,” the diaphragm contracts and the life-giving process of breathing begins.

The Diaphragm’s Role in Breathing

Although breathing is complex, we can break it into two components: (1) there is a “pump” that makes air move in and out, and (2) there is a gas exchanger that gets oxygen in and carbon dioxide out. The diaphragm’s primary role is on the pump side.

When the diaphragm contracts, it flattens out, pushing down on the abdominal organs. This causes the lungs and chest cavity to expand. When the lungs and chest cavity expand, it increases their volume and therefore reduces their pressure. This creates a pressure gradient: the pressure in the atmosphere is greater than in the lungs.

Since air moves from high to low pressure, this causes air moves from the atmosphere into the lungs. This is called inhaling. During exhalation, the diaphragm relaxes back to its original position, reducing the volume of the lungs and chest cavity. This reverses the pressure gradient, causing air to move out of the lungs. This is called exhaling. (Note: Although the diaphragm is the primary breathing muscle, keep in mind that it works in unison with the muscles in the ribs to execute each breath.) Now we know the diaphragm’s role in breathing, let’s next look at how it helps us relax.

Why Diaphragmatic Breathing is Relaxing

Slow, deep, diaphragmatic breathing has consistently been shown to reduce stress and anxiety. In fact, it represents possibly the fastest and most efficient way to deal with these issues. Many factors contribute to this, but a major one is that the diaphragm is innervated by the vagus nerve.
The vagus nerve is the primary nerve of the parasympathetic (rest-and-digest) side of the nervous system. When we breathe slowly and deeply, activating our diaphragm, the vagus nerve sends messages to the brain that we’re safe and everything is ok. The brain receives these messages and then redistributes them to the rest of the body. In this way, it triggers a positive feedback loop: relaxation begets relaxation.

How to Get Started with Diaphragmatic Breathing

There are several advanced exercises for activating our diaphragms. But this beginner’s one is all you need to begin feeling the benefits of diaphragmatic breathing for yourself.
  1. Lie on your back with your knees bent and feet flat on the floor.
  2. Place one hand on your abdomen and one on your chest.
  3. Breathe in softly and deeply through your nose, ensuring the hand on your abdomen moves while the one on your chest remains still. (This need not be a “big” breath, just a deep, relaxed one.)
  4. Exhale through pursed lips like you’re blowing on hot soup, trying to ensure your exhalation is longer than your inhalation.
  5. Continue for at least 1-2 minutes to feel the benefits.
  6. Build up to 20 minutes daily for maximum benefits.
Once this exercise is comfortable for you, transition to a seated position for an added challenge, which will help strengthen and engage your diaphragm even more.

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