What do a soda can and your trunk have in common?

Quarterly Question
Usually questions of the month come from questions parents ask us.  This question is a bit different – it comes from a question physical therapist Miriam Cohen posed when discussing breathing and function with the mother of a client.  (Hint, this is a question to be taken seriously… it’s not a silly riddle!) 

Q: What do a soda can and your trunk have in common?

A:  A soda can can be used as a model for the trunk to help us understand the importance of the trunk as a pressure regulator that needs to work efficiently both for postural support and, of course, for breathing.  (Massery, 2011)

The vocal folds are the top of the can. The diaphragm rests horizontally across the middle of the can and the pelvic floor muscles represent the base of the can. The rib cage and intercostal muscles (and lungs housed inside!) are at the top part of the can’s cylinder. Abdominal muscles, including the abdominal obliques, rectus abdominus and transversus abdominus, represent the bottom half of the cylinder.

Imagine the sturdy nature of a full, unopened can of soda. You couldn’t crush a full soda can due to its high internal pressure but could easily crush a punctured soda can with one hand. Just as the integrity of a soda can is based on balanced pressures within the can (think about what a full unopened can of soda feels like versus one of those cans that, for some reason, wasn’t filled up or has been punctured) the integrity of the trunk is influenced by its internal pressure and the integrity of the surrounding tissues.

If there is Weakening/damage of a part of the can (aka trunk), the can itself would be structurally weakened, the internal pressure would be affected, and the can could potentially collapse. Similarly when there’s a physical breach within the trunk, such as paralyzed vocal folds, a trachea with an incision or hole in it, a gap between the two sides of the rectus abdominus muscle, or weak abdominal oblique muscles , the integrity of the trunk system itself weakens, and becomes less efficient and functionally effective. The diaphragm, traditionally known as a breathing muscle, is also a critical muscle related to postural control and pressure regulation in the trunk. Therefore, it is necessary to incorporate specific movements with inhalation and other specific movements with exhalation to tap into efficient use of both the diaphragm and other skeletal muscles.

Breathing patterns influence our musculoskeletal structures.  And, musculoskeletal structures can influence our breathing patterns. A trunk with a breach in its pressure system is especially susceptible to the powerful downward pull of gravity, which always “wins”, and the skeletal system begins its collapse.  Our muscles, bones and internal organs are all interconnected (and connected with our breathing!) and must not be overlooked!!  

Miriam is a seasoned teacher assistant for Mary Massery, PT, DPT DSc.  She assists with Dr. Massery’s “If You Can’t Breathe, You Can’t Function”,“Proprioceptive Neuromuscular Facilitation” and “I Survived, Now What?: Treating the Musculoskeletal Consequences of Maturing with a Chronic Health Condition” courses. These courses are highly relevant to Miriam’s assessment and treatment. What she helps teach in courses she brings into easily understandable terms as she teaches both parents and co-workers at Pediatric Therapeutics.

–Miriam Cohen, PT. DPT, PCS

Massery M. The effect of airway control on postural stability (doctoral dissertation). Provo, UT: Rocky Mountain University of Health Professions; 2011.

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