Introduction

The diaphragm is an amazing muscle; it is a marvel that this muscle operates ceaselessly, from our first inhalation when we come into this world, to our last exhalation when we leave the world! It pumps air continuously 24/7, when we wake up and when we sleep. It never gets tiring. The skeletal muscles that move our body cannot work non-stop, and when they get tired, they need quite a lot of time to recover. If the diaphragm gets tired (in aerobic exercises), it is enough to resume normal breathing for a few cycles in order for the diaphragm to recover. It is always ready to serve us!

B.K.S. Iyengar said ‘the diaphragm is the window of the self‘, and stressed the importance of a freely moving diaphragm for maintaining good health. One cannot exaggerate the importance of this unique muscle. This article explains briefly the anatomy and action of the diaphragm, I survey both the mechanics of normal and Pranayamic breathing and suggest an exploration that helps to visualize the structure and operation of the diaphragm.

The diaphragm is both a voluntary and non-voluntary muscle

The only other muscle in our body that works non-stop is the other pump we have – the heart muscle. But we cannot really control this muscle; it is a non-voluntary muscle (it is said that some distinguished Yogis, like Krishnamacharia, can stop the heartbeats for a few minutes, but this is a very very special ability). What is very unique and special about the diaphragm is that it operates both voluntarily and involuntarily. The skeletal muscles do not contract without our conscious, deliberate will. The internal smooth muscles, like the muscles of the digestive system, and the heart muscle operate involuntarily. We cannot directly instruct them to work, and we cannot stop them from working – they function automatically. In contrast, the diaphragm functions most of the time involuntarily (even when we are asleep or unconscious), but we can control it and modulate its action, and even stop it for a few minutes.

A short anatomy of the diaphragm

The diaphragm is a very massive muscle situated in the center of the body. It completely separates the body into upper and lower parts. It is the floor of the thoracic cavity and the roof of the abdominal cavity. It is a large domed shape muscle – you can imagine it as a mushroom, a jellyfish or a bell. There are three holes in this otherwise impenetrable tissue, two for the main blood vessels (artery and vein) and another one for the esophagus.

Figure 1 The diaphragm is a domed shape muscle with the central tendon on the top

In fact the diaphragm has an asymmetrical double-dome shape. The right dome, which is pushed up from below by the liver, rises higher than the left dome (which is pushed down by the heart). Each half is innervated separately, so we can contract each half of the diaphragm independently from the other half and thus direct the breath to the left or to the right lung.

Try it now:

Place your fingers on the ribs and direct your breath only to the right side of the chest. Feel the movement of the ribs. Breathe slowly until the right lung is full.

Then exhale and breathe to the left lung. Repeat several times.

Now breathe in a zigzag fashion: breath for a few seconds to the right, then to the left, again to the right, and so on, until both lungs are full.

Origin and Insertion

The lower edges of the diaphragm’s circumference originate from three distinct regions: the xiphoid process (bottom of the sternum), the base of the rib cage, and the front of the lumbar vertebrae. The muscular fibers of the diaphragm rise vertically upward in the body from their origin and arrive at a flat horizontal top – the central tendon – to which they insert. This central tendon is non-contractile and can move only in response to the action of the vertical muscle fibers which insert into it (see figure 1).

This structure is unique: skeletal muscles always connect two bones (origin and insertion), while the dome-shaped diaphragm inserts into itself. Generally, a muscle can only contract, and in a non-isometric contraction, this reduces the distance between its origin and insertion. If the origin is fixed and the insertion is free, then the insertion is drawn closer to the origin; if however the insertion is fixed and the origin is free, then the origin is moved toward the insertion. For example, when the biceps muscle of the upper arm contracts, it draws the forearm closer to the upper arm (if the forearm is free). But if the forearm is fixed (as in Pull-ups) it will move the upper arm toward the forearm.

The Breathing Mechanism

The diaphragm is the main breathing muscle, without it, independent breathing is impossible. We know this because people that, for some reason, cannot use the diaphragm cannot breathe on their own and need an artificial ventilator. The other respiratory muscles are only auxiliary and are not sufficient for efficient breathing. They are just not strong enough to be able to increase sufficiently the volume of the chest cavity.

As in any other muscle, the contracting fibers of the diaphragm pull its insertion (the central tendon) and origin (the base of the rib cage) toward each other. The movement that actually takes place depends on which side is fixed and which is free to move.

In normal, natural breathing, inhalation is an active contraction of the diaphragm, and exhalation is a passive release of this muscle. If the abdomen is soft, the central tendon is pretty much free to move and the contraction of the diaphragm during inhalation shortens its fibers which pulls the central tendon down. The abdomen then slightly bulges out. This increases the volume of the chest cavity and decreases the pressure in the chest cavity, which causes air to flow in. When we release the diaphragm, the central tendon moves back up and the air is pushed out of the lungs (see figure 2).

Figure 2 Three-dimensional thoracic shape changes of (a) inhalation and (b) exhalation

Note that this downward movement of the central tendon, which occurs during inhalation, increases the pressure in the abdominal cavity. When we breathe deeper, the resistance of the organs of the upper abdomen makes the downward movement of the tendon more difficult and this causes the ribs to lift slightly. So actually, even in a normal deeper breath, the downward movement of the central tendon is combined with a lift of the lower ribs.

In Pranayamic breathing (as done according to the Iyengar method) we attempt to lift and open the rib cage and do it in a slow, soft and subtle manner, without creating any tension in the eyes, ears, or brain cells. In order to achieve this, we have to use the diaphragm in a different mode of operation. This is done by gently sucking the abdomen in at the end of exhalation, and keep it pulled in when we inhale. This action of the abdominal muscles (mainly the transversus abdominus) does not allow the central tendon to move down. This is called Uddiyana Kriya (in contrast with Uddiyana Bandha which is a strong contraction and locking of the abdominal region, done at the end of a complete exhalation).

By keeping this action of Uddiyana Kriya while inhaling, we prevent the central tendon from moving down, and this result causes the rib cage to lift and expand. As we get more proficient in controlling the action of the diaphragm, we learn to do this action in a slow and rhythmical way. This makes the inhalation long and smooth, and the brain becomes soft and receptive. As we lower the head in Jalandhara Bandha, the mind is drawn in and gets totally absorbed in the process of breathing. In that stage, there is no more ‘I’ that breathes, and only the breath remains.

Conclusion

Understanding the uniqueness of the structure and action of the diaphragm enables us to apprehend B.K.S. Iyengar’s saying that ‘the diaphragm is the meeting point of the material world with the spiritual world’. In an interview with Carol Cavanaugh he said:

“The diaphragm balances our physical and mental bodies. When people suffer from a catastrophe, depression, sorrows, and misery, they say their solar plexus – the navel region, is tight and cramped. Why? What is the medium of our existence? It is the diaphragm…

Tension and pressure make the diaphragm harder… The diaphragm is the window of the self. The more tension you have, the more the window of the diaphragm gets closed. if the diaphragm is spread, it takes any load, whether intellectual, emotional or physical.” (See: Astadala Yoga Mala, Vol. 4, p. 86)

Our life depends on the efficient functioning of this muscle and our quality of life depends largely on our skillful use of it. By observing its operation we can come closer to realizing the marvel and wonder of life that we tend to take for granted and get some glimpse into the operation of the universal energy which the yogis call: Prana – the energy of Life. Developing intimate relationships with our breath makes us humble – since we realize that the breath is not in our hands, it is created and sustained not by our ego, but by a power which is far greater than us, to which we can call Divinity. This experience changes our attitude: instead of feeling great, you feel grateful!