The Diaphragm – More Than Just a Muscle

“There is arguably no other muscle in the human body that is so central literally and figuratively to our physical, biochemical and emotional health as the diaphragm. From its obvious role in respiration to its less obvious roles in postural stability, spinal decompression, fluid dynamics, visceral health and emotional regulation, the diaphragm has a repertoire of function that is broad by any muscle’s standard.”

– Matt Wallden MSc Ost Med, BSc (Hons) Ost Med, DO, ND doi:10.1016/j.jbmt.2017.03.013

It became obvious early on in my career that the diaphragm was central to the rehabilitation of not just the spine, but of all four limbs as well. What wasn’t as obvious at the time was the fact that the diaphragm has a function or an influence on every system of the body. Once I wrapped my head around this, I started to include diaphragmatic breath as a component, if not the first component, of every patient’s treatment plan. Similar to myself as a new grad, I find that many people don’t quite understand how important diaphragmatic breath is and let’s face it, focusing on breath is pretty boring especially when you are looking to decrease pain and get strong. But once you know the why behind it all, I think you will start questioning any health professional that doesn’t put an emphasis on diaphragmatic breath.

Embryologic Connections

Before I dive into what the diaphragm does, let’s talk about where the diaphragm comes from as in what tissue it is derived from when we are a ball of cells turning into a tiny human in utero. There are 5 major contributors to the formation of the diaphragm:

  1. Mesoderm (from the third and/or fourth cervical myotome…various articles cite different levels)
  2. Pleuroperitoneal membrane (also forms pericardium)
  3. Esophagus (contributes a layer of connective tissue where it passes through the diaphragm)
  4. Anterior body wall (also forms abdominals, intercostals, scalenes and pelvic floor)

I know there are a lot of big words in there and for anyone that isn’t an anatomy nerd like myself, that list may mean nothing to you which is totally fine. Here is the big take away: the tissues that form the diaphragm come from the neck and also go to form the sac around the heart, the esophagus, the abdominals, pelvic floor and muscles in the neck. This can give us a little insight into how connected the diaphragm is to the neck, abdomen, heart, esophagus and pelvic floor. It also means that dysfunction in the diaphragm can result in heart problems, swallowing issues, neck pain, incontinence and spinal instability.

Anatomical Connections

Ok let’s get into what the diaphragm looks like once we are all grown up or at least out of our mama’s belly. Many research articles go into ridiculous anatomical detail describing the diaphragm, I will spare you all of those words and highlight some fascinating anatomical connections that may give light into how this muscle has interplay with so many surrounding structures.

First off, it’s important to note that the diaphragm is a dome shape at rest and flattens when it contracts. This is unlike most muscles in our body other than the pelvic floor. The diaphragm supports the lungs and heart from above while sitting on top of the liver and stomach below. The front portion is connected to the tip of our sternum (xiphoid process), the side portion is attached to the inside surface of our lower 6 ribs and the back portion is attached to the upper segments of the low back in addition to the arcuate ligaments that extend out to both sides and wrap around the trunk. This means that any rib or lumbar spine dysfunction will influence the diaphragm’s ability to contract and relax and vice versa. It’s also important to note that the arcuate ligament fascia is blended with the quadratus lumborum, psoas and transversus abdominis so any disruption in these muscles could either drive or be caused by diaphragm dysfunction.

The diaphragm also has ligaments that attach the muscle to the viscera. This includes an attachment to the base of the lungs, one to the heart, two to the liver and a few to the intestines. Whoa right?! I hope you are starting to grasp how connected the diaphragm is to practically everything above and below it on a structural level.

Neural Connections

The diaphragm is also connected to most everything through its neural innervation aka what nerves make up the pathway for a signal to come from the brain to the muscle and back to the brain. The diaphragm receives both motor and sensory signals from the phrenic nerve which is comprised of spinal nerves C3, C4 and C5 (sometimes C6). These spinal nerves are also involved in making up the cervical and brachial plexus so any abnormal signaling from the diaphragm may alter motor control in the neck and into the shoulder and arm. This implies that shoulder and neck pain could be a symptom of diaphragm dysfunction.

The pathway of the phrenic nerve gives even further insight into what can influence messages sent to and from the diaphragm. Upon exiting the spine, the phrenic nerve goes through the anterior scalene muscle. This muscle is located at the front of the neck and is very vulnerable to injury with whiplash. It is also put under a large amount of stress with forward head posture.

The phrenic nerve later blends with the vagus nerve as it passes through the opening in diaphragm on its way down into the abdomen. This is how diaphragmatic breath can assist in “massaging” the vagus nerve thus putting our body in rest and digest mode instead of fight or flight. I mean that function alone makes diaphragmatic breath worth any effort it takes to find it.

“The diaphragm is one of the most remarkable areas of the body in that it has so much influence and the consequences of its dysfunction can manifest anywhere from the head to the toes”

Caroline Stone. Science in the art of osteopathy. Osteopathic prin- ciples and practice. Stanley Thornes Ltd, Cheltenham 1999.

Respiratory Function

You would think I would be done there but we haven’t even talked about the actual functions of the diaphragm yet! Let’s start with the most obvious role as the prime mover of breathing. When the diaphragm contracts (flattens) it creates a negative pressure in the chest to draw air in. Then when it relaxes (domes) it pushes air out. It is designed to match the demands of an activity and controls our ability to go from whispering to yelling.

Postural Function

While I consider respiration to be absolutely essential to human life, my main interest in diaphragmatic function has always been its role in postural stability because it is most directly correlated with pain-free function.

When the diaphragm contracts, it increases intra-abdominal pressure which then stabilizes the spine but studies have also shown that the diaphragm contracts to stabilize regardless of the phase of respiration. In other words, the diaphragm stabilizes the spine indirectly through intra-abdominal pressure but also directly through stiffness generated by a contraction.

Research has demonstrated that the diaphragm is one of the first muscles to contract in preparation to lift something or move a limb. It has also been shown that individuals with limited ability to contract their diaphragm for stabilization and those with uncoordinated diaphragm activation have a higher likelihood of back pain.

While the diaphragm is able to perform respiration and stabilization at the same time, the stabilizing contraction will decrease as the respiratory demand increases. This makes sense in that our ability to breathe and oxygenate our brain is far more important than spinal stability for survival so it’s the first to go. Those that have low back pain are shown to have earlier respiratory fatigue aka the stabilizing function drops off sooner at lesser respiratory loads.

Gastro-Esophageal Function

In my opinion, the most surprising function of the diaphragm is its role in swallowing, vomiting and prevention of stomach contents refluxing up into the esophagus. I was amazed not by the what but the how of this function.

There are actually two parts of the diaphragm, the crural portion and the costal portion. Up to this point I have been mostly talking about the costal portion which is the perimeter of the muscle. The central portion in the crural part.

But that’s not the cool part. These two parts actually work separate of each other to allow for swallowing and vomiting. For example, in vomiting, the crural (central) part relaxes to allow for ejection of the stomach contents while the costal (outer) part contracts with the abdominals to increase intra-abdominal pressure to force the contents outward. Crazy right?! The vagus nerve is what innervates the crural portion of the diaphragm so sympathetic tone could be a contributor to acid reflux.

Lymphatic Influence

The diaphragm is also the primary mover of organs. I included the video above to illustrate just how much movement occurs in an individual that diaphragmatically breathes. This massaging of the organs is important not only for proper organ function but also for the drainage of lymph (fluid). Sixty percent of lymph nodes are located just under the diaphragm. The rhythm of diaphragmatic breath stimulates the cleansing of these nodes by creating negative pressure pulling the lymph fluid back into the lymphatic system.

Contraction of the diaphragm also narrows the diameter of the vena cava thus assisting in the return of blood back to the heart. Therefore, if someone has swelling in their lower limbs, diaphragmatic function should be assessed.

Cardiac Influence

There are a few ways the diaphragm effects the cardiovascular system. As I just mentioned above, it promotes venous return by narrowing the vena cava but it also does this by creating a pressure gradient facilitating the flow of blood back to the heart. This effect is maximized in slow and deep respiration. Another connection already noted is the ligament that goes from the heart to the diaphragm. This means that a lack of diaphragmatic movement may reduce the ability of the heart to contract and therefore impair blood circulation.

Heart rate is also heavily influenced by respiration. On an inhale heart rate increases and it decreases on an exhale. This cyclic change in heart rate is known as respiratory sinus arrhythmia (RSA) and is thought to improve gas exchange in the lungs.

If we just look at heart rate as it is measured through pulse, diaphragmatic breath decreases it by reducing sympathetic (fight or flight) activity. This is accomplished by stimulation of the vagus nerve and activation of the hering-breur reflex through an increase in tidal volume (amount of air passing through lungs).

Emotional Influence

The separation between heart and emotional influence of the diaphragm is a blurry line. A local entity called Heartmath (https://www.heartmath.com) has done a ton of research connecting stress to an increase in what they call heart rate variability which is the amount of change in heart rate between inhalation and exhalation aka RSA. They have shown through extensive research that heart rate variability (and therefore our stress response) is improved with diaphragmatic breath. Blood pressure and other parameters of cardiac function are also improved. The overall conclusion is that emotional states affect the diaphragm and vice versa, the degree of which is measured through RSA. If any of you have the Apple Watch, it uses heart rate variability (aka RSA) as a trigger to remind you to breath. And I’m sure most of you have experienced this connection in life. When under acute stress, your breath will shorten and move upward into your chest while your heart rate increases. If you haven’t been aware of this up to this point, pause for a moment the next time you are stressed. Acknowledge the sensation of this physiological shift and then focus on diaphragmatic breath to return back to homeostasis. Its powerful stuff.

The diaphragm is also the muscle that is responsible for the expression of emotions so it makes sense that it is a key component of somatoemotional release techniques. Physical expression of stress and emotions occurs when we don’t release them. The act of crying involves a sharp inhale (aka a diaphragmatic contraction) followed by a pause and then wailing followed by further gasps of air and further wailing. The gulps of air are diaphragmatic contractions and the wailing is an abdominal contraction with diaphragmatic relaxation. The act of crying is pain/emotional tension being exported from the nervous system. If we don’t cry and we hold our breath, the diaphragm may hold this tension while the abdominals are off and distended. Long story short, this isn’t good.

“By (diaphragm) action we live, and by its failure we shrink, or swell, or die”

Andrew Still. Philosophy of osteopathy. Mo: A.T. Still, Kirksville 1899.

So why spend all this time learning about the diaphragm and all it does? Most of us don’t diaphragmatically breathe. In fact 83% of those with anxiety have a dysfunctional breathing pattern. And who isn’t anxious these days? In other words, this information is applicable to almost every single one of you. So the next time we start your treatment working on breath, you will know exactly why.

Want to see the research?

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Respiratory Sinus ArrhythmiaYasuma, Fumihiko et al.CHEST, Volume 125, Issue 2, 683 – 690 https://doi.org/10.1378/chest.125.2.683

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