What is the Zone of Apposition? 

The Zone of Apposition is defined as the area of attachment between the diaphragm directly behind the inner aspect of the lower chest wall and rib cage. This area is of great importance for proper diaphragm and breathing function, and depends largely on the anatomical positioning of the muscle to the rib cage. 

The Diaphragm 

The diaphragm is a dome-shaped muscle located in the chest cavity and separates the thoracic and abdominal cavities. It consists of a central tendon and inserts onto the upper lumbar vertebrae, and on the lower chest wall and rib cage, forming the ZOA. During inspiration, the diaphragm descends, while the rib cage expands outward creating a negative pressure to allow air to enter the lungs. Additionally, as the diaphragm fibers contract and shorten, the ZOA is maintained through abdominal and oblique muscle tension. Furthermore, efficiency of the diaphragm, and thus the maintenance of the ZOA, is affected by accessory respiratory muscle overuse, changes in chest wall and rib mobility, and lung hyperinflation. 

What is an optimal ZOA?

In general, the ZOA constitutes about 40% of the rib cage at rest, and changes (decreases) with both passive (involuntary) and active breathing patterns as the diaphragm contracts and shortens. in short, the ribs are able to externally rotate (move up) or internally rotate (move down). When the ribs externally rotate, the diaphragm loses contact with the ribs, thus decreasing the ZOA, and restricting efficient breathing patterns, causing accessory respiratory muscle usage and inefficiency of the abdominal muscles. Moreover, the ribs become externally rotated by loss of muscle tone causing lumbar lordosis, or low back arching, and anterior pelvic tilting. Therefore, in order to achieve an optimal ZOA, then ribs must be in an internally rotated position by increasing the resting tone of the abdominal muscles to maintain neutral spinal alignment. 

Dysfunctional ZOA

ZOA can be lost, or dysfunctional, most commonly on one side, but can also be lost on both sides as well. When apposition is lost on one side, it is almost always on the left side, and often due to a loss of abdominal muscle efficiency on one side, whether it is hypertonic muscles or abdominal weakness, leading to opposite side chest wall expansion and hyperinflation, especially during gait. Another cause of a dysfunctional ZOA is accessory muscle breathing. Respiratory accessory muscles include the sternocleidomastoid, upper trapezius muscle, and pectorals, which are often hypertonic and over-developed in the presence of a lack of abdominal muscle strength and efficiency.. Additionally, the thoracolumbar extensor muscles running along the spine are often over-active, causing changes in the chest wall shape and creating a sub-optimal ZOA. 

Suggested Interventions

Increase the strength of the deficit muscle groups - 

*Supine hollow body : 2 x 20

* Feet elevated lumbar flexion and extension: 2 x 20 

References

1. Petroll WM, Knight H, Rochester DF. Effect of lower rib cage expansion and diaphragm shortening on the zone of apposition. J Appl Physiol (1985). 1990 Feb;68(2):484-8. doi: 10.1152/jappl.1990.68.2.484. PMID: 2318760.
2. Diaphragm function & core stability » Hans Lindgren DC. (n.d.). Retrieved September 24, 2020, from http://www.hanslindgren.com/articles/diaphragm-function-and-core-stability/
3. What Is the Zone of Apposition? - PRI Trainer. (n.d.). Retrieved September 24, 2020, from https://pritrainer.com/what-is-the-zone-of-apposition/
4. Zone of Apposition. (n.d.). Retrieved September 24, 2020, from https://www.posturalrestoration.com/the-science/zone-of-apposition-zoa