Breathing and Postural Control

By: Jessica Pulliam, DPT

One of the top buzzwords of fitness and wellness today is “core.” The mainstream perception of a strong core is to have a stomach with “six-pack” abdominals. The reality is that a strong trunk is much more complicated than having a nice looking stomach. Strong abdominals are a component of trunk stability, but healthy respiration and a strong pelvic floor also contribute to stability that will reduce incidence of injury3. A popular analogy to explain this relationship is a soda can. The can consists of a top and bottom, side supports, and a pressure system to support the structure. When a soda can is full and sealed it is nearly impossible to crush. However, as soon as it is dented or the top is open the structure becomes vulnerable to external forces. The structural stability of the trunk relies on pressure control, similar to the structure of a soda can4.

Consider your trunk as a can that consists of cylindrical sides, top, bottom, and an internal valve. The sides are comprised of layers of abdominals to support the spine and ribs. These muscles are the rectus abdominis, transversus abdominis, internal obliquus, external obliquus, as well as the intercostal muscles (Figure 1).

In order to seal the structure, there are two external valves at the top and the bottom of the trunk: the vocal folds and the pelvic floor. The top valve is controlled by the vocal folds, which help to regulate thoracic pressure. The ability of the vocal folds to seal off the thoracic cavity and create positive pressure is crucial for several functions such as postural support and the ability to “bear down” to void bowels. On the bottom end of the can, the supporting structure is the pelvic floor. This holds the responsibility for supporting internal organs, healthy sexual function, and continence. A strong pelvic floor helps close the system and plays a role in trunk stability5. The internal valve is the diaphragm, which is a major pressure regulator. The diaphragm is a thin layer of muscle that divides the thoracic cavity from the abdominal cavity. It is shaped like a parachute and when it flattens out in contraction, it creates negative pressure in the thoracic cavity (Figure 2). That negative pressure initiates an inhalation, aided by the contraction of inspiratory muscles. The pressure system that the diaphragm creates also contributes to postural support, and digestion, and it aids with venous return to regulate blood pressure3.

Any weakening of this system compromises the trunk’s ability to close the system and has a negative impact on core stability. This may manifest in several ways but is most commonly associated with low back pain, incontinence, and constipation5. True core health should be thought of as a three dimensional structure that is maintained with intricate pressure control and motor coordination. When you have anatomy this elegant, who would bother with a six-pack?


  1. The Editors of Encylopaedia Britannica. Encylopaedia Britannica. 2009; Accessed December 4, 2016.
  2. Ng B. Essentrics with Betty 2016; Accessed December 4 2016.
  3. Key J. ‘The core’: understanding it, and retraining its dysfunction. Journal of bodywork and movement therapies. 2013;17(4):541-559.
  4. M Massery HM, Stafford R, Moerchen V, Hodges PW. . Effect of airway control by glottal structures on postural stability. . Journal of Applied Physiology 2013;115(4):483-490.
  5. Bo K. Urinary incontinence, pelvic floor dysfunction, exercise and sport. Sports medicine (Auckland, NZ). 2004;34(7):451-464.

About the Author:

Jessica Pulliam recently earned her Doctor of Physical Therapy diploma from the University of Colorado Anschutz Medical Campus. She has a professional interest in both neurological rehabilitation and in pelvic floor health. Personal interests include travel, cooking, yoga, and the outdoors.