A side stitch is a cramping in the diaphragm muscles, which separates the thoracic cavity (chest cavity), where you heart and lungs reside, from the abdomenal cavity where the liver, stomach, kidneys and other organs used for digesting and processing energy and nutrients reside.
The interesting thing about the thoracid cavity (chest cavity) is that it is sealed so that the lungs are in a vacuum. You inhale (fill your lungs), not bo pushing air into them, but by expanding the chest, which pulls the lungs open, so that air has to flow into your mouth and/or nose to fill the space. Exhaling is as simple as relaxing the muscles you just used to expand your thoracic cavity, although you can also apply force to push the air back out more quickly, in case your body requires faster breathing to provide a greater supply of oxygen to tissues that are working harder.
The diaphragm is one of the primary muscles used when we inhale. Relaxed, it stretches out and has an upward bow to it, so that when contracted it pulls down and become more flat, expanding the interior volume of the thoracic cavity. By pulling down to expand the thoracic cavity, which is fairly rigid due to the support of our ribs, the diaphragm also compresses the abdominal cavity, and you might notice that when you inhale your stomach expands, although no air should be entering your abdomen.
Some of the abdominal organs (like the liver and stomach) are suspended from the diaphragm by connective tissues called ligaments, too, so when you’re walking around, your guts aren’t all just coiled down into your pelvis like it’s some kind of bucket. So, you can imagine that when you run, your liver and stomach bounce up and down, applying their own forces to the diaphragm. read more…
