What Is Posture Skip George

Unlocking Secrets of the Thorax Part One: Essentials that Define the Zone of Apposition

With every breath you take and every move you make (1), one structure has the power to determine not only how you breathe and walk but also influences posture and the position and of every joint in the human body.   Its position, shape and ability to relax during the breathing cycle directly affects blood chemistry, the parasympathetic nervous system and even our ability to hit a fastball over centerfield. This structure also plays a role with every patient that walks into your clinic with lumbar pain, neck pain, headaches or the inability to fully internally rotate a shoulder!

The structure is the diaphragm. Its shape and positioning nestled closely to the inside of the ribcage is called the “Zone of Apposition” (ZOA)(2).   Understanding and providing a ZOA, especially the left side of the diaphragm, is perhaps the most essential structural issue required for assessing and treating position and alignment of the pelvis and spine, posture of the entire skeletal system and reciprocal and alternating movement while breathing and walking.(5)

What is Posture Postural Restoration InstituteThe ZOA is defined as the domed shape of the diaphragm that coincides with the space inside the chest wall between the interior portion of the ribs and at the anterior thoraco-lumbar spine or posterior mediastinum.(2) The ability to inhibit or relax the diaphragm and create a ZOA is determined by the position of the ribcage and the ability to fully exhale. The absence of a ZOA results in a chronically flattened diaphragm that is hypertonic and prevents counter rotation of the thorax.

When the diaphragm relaxes or inhibits during exhalation and becomes more domed shaped, it is assisted by the facilitation of the ipsilateral anterolateral abdominal wall. The internal obliques, transverse abdominis and the triangularis sternum “oppose” the diaphragm by pulling the lower ribcage down and into internal rotation. When this happens, the chest wall shrinks or gets smaller as the air moves out of the chest wall.

Believe it or not, we don’t breathe symmetrically. This breathing asymmetry is especially true when walking or moving. One side of our chest wall is always in a state of more or less inhalation or exhalation than the other.

In previous articles (Unlocking the Secrets of the Pelvis), I’ve mentioned the fact that we that we are all born “standard issue” with static asymmetries that underlie functional asymmetries we acquire overtime that lead to dominate overuse of one side of our body. They include a left dominate brain for motor skills and a right brain stronger in creativity. We are born with three lobes of lung on the right with two lobes on the left with a dome of the liver on the right side just under the right side of the diaphragm. The liver aids in creating a domed shape of the right diaphragm. The heart and blood vessels are located left central above the left side of the diaphragm and this anatomical arrangement in the left chest wall facilitates a more flat or tonic left hemi-diaphragm.(4)

Visualize the diaphragm on both sides of the chest wall connecting to the sternum, ribcage and lumbar spine. Big “D”, or the diaphragm, is a structure with a right and left hemisphere. The right hemi-diaphragm is bigger, stronger and has crural attachments reaching down to the spine that connect 1 ½ to 2 lumbar levels lower than on the left. This difference in attachment level plus asymmetrical tone of the diaphragm contributes to spinal curvature and position. Since the left hemi-diaphragm does not have the liver to assist it in creating an anatomically positioned dome, it tends to be flatter and this is one reason for its hyper-tonicity. The consequence is the left diaphragm and expanded left chest wall tend to be in a state of inhalation more so than the right. This left/right difference in inhalation/exhalation is determined by the direction of movement of the ribcage and the ribcage determines the direction and movement of the spine.

When we breathe in, the diaphragm descends and it flattens out. When we exhale the diaphragm “domes” and becomes inhibited or relaxed. Because the asymmetries we are born with, the right side tends to dome better because of the liver below and a natural tendency for our ribs on the right anterior lateral chest wall to internally rotate and decrease the size of the right hemi-thorax.

When the diaphragm becomes hypertonic and the ribs externally rotate, as it usually does on the left to a greater degree than the right, it directs a sequence of muscles that connect to it called a polyarticular chain. The first muscle the diaphragm has an intimate relationship with is the psoas. The psoas connects below the diaphragm to the anterior portion of the transverse process and bodies of the lower lumbar vertebrae. What makes this relationship intimate is that where the fibers of the crura connect to the lumbar spine and the psoas fibers from below connect at the same level, those fibers at that connection point of the diaphragm and the psoas are essentially indistinguishable! It is as if they are one muscle and in fact they operate as one and begin the left anterior interior chain. (L AIC) (3)

When the diaphragm becomes hypertonic in an inhaled state, the psoas follows right along with increased tonicity. Both muscles function together to help orient the pelvis, sacrum and lumbar spine to the right and onto the right leg.

This is called right mid- stance and we all do it! The problem is most of us get stuck in right mid- stance. Getting stuck in right mid-stance is a result of not being able to inhibit the diaphragm on the left side or the chains of muscles that connect to it going down the left lower extremity and up into the right chest wall, shoulder, neck and cranium(6)! Now we begin to at least get a general idea that the diaphragm has significance to every joint in the kinetic chain head to toe!

This is where every breath you take and every move you make begins to make more sense. That is, two important issues drive lumbo-pelvic-femoral myokinematics as well as ribcage movement. The first is air and the ability to move it from the left chest wall to the right chest wall and back again. The right chest wall tends to be in a state of exhalation because of the natural dome of the diaphragm and because we are driven over to our right side by a hypertonic polyarticular chain of muscles starting with the left diaphragm continuing down into the left pelvis and leg.(3)

So how do we get the left diaphragm to relax or inhibit? The first problem is that the entire diaphragm is a muscle of inhalation. Imagine that left diaphragm, more so than the right, as being flatter and in a perpetual state of inhalation dominance for your patients. They are trying to inhale in a state of inhalation. The only thing left to help them pull air in is a dysfunctional reliance on accessory muscles of respiration including the scalenes, traps, levator scapulae, SCM’s and the latisumus dorsi.(6) What makes the lat’s accessory muscles is that one way to help get air in is to extend a back and the lats are strong in extension of the spine. The flattened diaphragm now becomes positioned to pull the lumbar spine forward into more extension as the ribs lift up in front even more in an attempt to get air in. In addition, the pelvis is pulled into a forward tilt or flexion widening the distance from the ribcage to the pelvis creating excessive lordosis of the lumbar spine and a loss of the normal kyphotic curve in the thoracic spine.

The next problem lies with our inability to exhale fully enough to let the diaphragm relax first before inhalation thereby relieving the accessory muscles of trying to pull air into an already inflated chest wall. The internal obliques (IO’S), transverse abdominis and triangularis sterni(5) are key players with exhalation and restoring functional ribcage biomechanics as well as a ZOA.

Let’s start with the internal obliques and visualize from the back. My good friends and mentors James Anderson, MPT, PRC and Mike Cantrell, MPT, PRC use the analogy that if you had a couple of “hay hooks” (used to lift bales of hay) and reached around someone from the back to the front and grabbed on to their lower ribs for the purpose of pulling the ribcage down and back then you have an idea of what the IO’s do. They pull the ribcage down in front so you can get air out and hold it down during inhalation so you can expand the thorax in a functional fashion.

The transverse abdominis (TA), especially on the left side, is needed to pull the ribs into internal rotation. With facilitation of the left IO’s, TA’s and triangularis sterni (which by the way is asymmetrically biased with and extra muscular rib attachment on the left), the ribs on the left can now pull the ribcage down instead of flaring and move the left side of the ribcage into internal rotation. If we can’t facilitate the muscles of exhalation on the left and get air from the left chest wall into the right, we tend to develop compensatory strategies of breathing and moving. In addition, if we can’t get air out of the left chest wall and into the right, we are stuck in right midstance while the polyarticular chains of muscles, called the left anterior interior chain (LAIC), remain in a state of hypertonicity driving us to our dominate right side and right leg.

In part two of Zone of Apposition I will discuss ways to identify the presence of a ZOA and its importance in rehabilitation and sports performance as well.


  1. “I’ll Be Watching You” The Police, Written by Sting, 1983 Album Synchronicity
  2. Zone of Apposition (ZOA), ZOA Position and Mechanical Function, Ron Hruska, pg. viii Postural Respiration course manual
  3. The Left Anterior Interior Chain Pattern, pg. vii Postural Respiration course manual
  4. Static Asymmetry, Pg. 2 Postural Respiration Course Manual
  5. Thoracic Wall Muscles, pg. 9-10, Postural Respiration course manual
  6. Differences Between the Left and Right Abdominals, Lower Trap and Serratus Anterior Function in the Left AIC/Right BC Pattern, James Anderson, MPT, PRC Postural Respiration course manual, pg. 16-17
  7. Hruska RJ: Influences of dysfunctional respiratory mechanics on orofacial pain. Dent Clin North Am 41:2, 1997. Breathing Discord
  8. DeTroyer A, Estenne M: Functional anatomy of the respiratory muscles. Clin Chest Med 9:2, 1988. Dynamic Asymmetry

Robert George, D.C., CCSP, CSCS, PRC is the first chiropractor to be certified by the Postural Restoration Institute (PRI). He is an internationally recognized speaker on topics relating to integrating chiropractic, rehabilitation, concussion and sports performance.   In addition he is now a faculty member of the Postural Restoration Institute and will be teaching the course “ Postural Respiration” this year.

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