Q:

Does the human abdominal cavity use pressure to maintain posture?

Several of my PT friends have referenced a physical therapist p who has studied breathing named Mary Massery. In her articles, she has referenced the idea of "intra-abdominal pressure"
http://www.masserypt.com/images/pdfs/Massery.%20Seating%20Symposium.%20Vancouver%202010.pdf
See page 2
If I am understanding her correctly, she is basically saying that 

an unopened soda can is sealed and hard because of the pressure inside the canister 
the human trunk tries to support itself upright. In this sense it is rigid. Therefore, it too must be using an internal pressure to create the rigidify necessary for uprightness. This is what she calls "intra-abdominal pressure."  

My Question
Given what is known about the mechanics of human breathing, do the pressures of the abdominal cavity actually behave this way? Does the abdominal cavity rigidity itself using some sort of pressure? If so, how does this pressure mechanism relate to the mechanisms used during respiration? 
If I am understanding her model correctly, I am extremely skeptical. A soda can is really not similar at all physically to the abdominal cavity. 

A:

I found this review which can help to clarify this notion of intra-abdominal pressure : Intensive Care Med. 2009 Jun;35(6):969-76. 
What is normal intra-abdominal pressure and how is it affected by positioning, body mass and positive end-expiratory pressure?
De Keulenaer BL1, De Waele JJ, Powell B, Malbrain ML. 
The authors mention that there is indeed a positive pressure in the normal subject. This IAP is contributed by gravity, uniform compression (abdominal contraction, diaphragmatic contraction, mechanical ventilation, rib cage excursions) and shear deformation, this last one depending on the intrinsic stabilty of the tissue.
The authors conclude that "the abdomen behaves as a hydraulic system with normal IAP of about 5–7 mmHg..". Kind of a can of soda, without the bubbles...
Pathologies affecting this pressure are named "abdominal compartment syndrome) and result from multiple etiologies (obesity, trauma...,).

