The pressure systems of the body and their effect on neuro-musculoskeletal function

In the physical therapy world, it is not often thought about how other systems of the body might affect the muscle pains and joint aches that are felt. A previous post briefly touched on how increasing pressure in the abdominal cavity helps to create stability in the trunk in an earlier post, here. This post will dive deeper into this and why it is important to understand.


The two main zones, when considering pressure systems of the trunk, are the abdominal/pelvic cavity and the thoracic cavity. The pelvic cavity consists of the pelvis and all of its visceral (organs) and musculoskeletal structures (muscles, tendons, and ligaments). The abdominal cavity is continuous with the pelvic cavity and consists of the abdominal viscera (organs such as the intestines), and musculoskeletal structures (muscles, tendons, and ligaments), such as the abdominals, lower back muscles, and the diaphragm. The thoracic cavity consists of everything above the diaphragm. This would include the viscera (organs) and musculoskeletal structures (muscle, tendon, ligaments) of the thoracic and rib cage up to the throat.


Imagine that the trunk (and the muscles in it) are a cylinder, like a soda can. The pelvic floor muscles are the bottom, the abdominals and lower back muscles are the sides of the can, and the diaphragm is the top (though we could take it further and talk about how the vocal cords may actually be the top! But maybe in another post). With a soda can, if it has not been opened, then there is a certain amount of pressure inside the can that makes that can very strong. One could stand on it and likely not crush it. Now, open the can, or keep it closed and put a dent in the side. If one tries to stand on it now, it will be easier to crush. This is partially due to the pressure in the can being changed.

Now apply that to the body. When all of the muscles of the trunk contract together, in synergy, it creates increased internal abdominal pressure. The thoracic cavity (chest) is separated from the abdominal cavity (stomach) by the diaphragm. The pressures in the thoracic cavity and the abdominal cavity balance each other out. This is part of creating stability (there is much more to this, but for the purposes of this post, let’s stop there). When this function is efficient, a person will feel stronger and be stronger. The body can withstand more stress and work without breaking down or becoming injured.

When this system is not efficient, this increased pressure is not created as well, or the balances of the pressure between the abdominal and thoracic cavity are changed, creating less stability and potentially increasing stress to other areas of your body.

When you are being treated and you are going through exercises that focus on the core, or having soft tissue work done, or joint work done, think about how your therapist might be effecting more than just those muscles or joints.We would be naive to think that when we perform soft tissue work, joint work, or exercises that we are only having an effect on those specific muscles or joints. Our body’s systems work in synergy with each other, and many systems rely on other systems to function efficiently.