Diaphragm cramp or side stitches, call it what you like it’s unpleasant. There are only theories as to why you get side stitches when you are running (or doing other sports activities). The most widely held belief is a muscle spasm of the diaphragm and/or its supporting ligaments.
Your diaphragm muscle assists you with breathing while you are running and because your need for oxygen increases when you’re running, your diaphragm works harder. The thought is that it gets tired and/or the surrounding tissues get tired and then the muscle spasms.
The second theory is improper breathing (oh yeah, you can breathe the wrong way). This theory ends the same as the above, a fatigued diaphragm and surrounding muscles which leads to spasms. The difference is breathing too shallow. Shallow breathing means your muscles don’t get enough oxygen and then get tired easier.
So what’s the proper way to breath when you are running? Deep with your belly not shallow into your chest. Breathing deep into your belly opens blood vessels found deep in your lungs and fills your blood with more oxygen. Most people breath with their chest, only filling two thirds of their lungs. To tell if you are belly breathing, lay on your back and lay your hand on your stomach. If your hand rises and falls you’re belly breathing. Most of us have to make a conscious effort to belly breath.
The third theory is we don’t time our breathing with our foot falls properly. When you are running try inhaling for three steps (right, left, right) and then exhale for two steps (left, right). This five-step rhythm will alternate your exhale from your right foot plant to your left. You have to think about it for a while when you’re first learning to do it, but it will reduce your side stitches. Practice it for a few minutes every mile and pretty soon it will become automatic. If you are climbing a hill or doing speed work, change it to a 2:1 ration for inhalation and exhalation.
The fourth theory is poor running posture, aka running with your shoulders rounded and your upper body bent forward. One belief is that hunching over like that compromises nerves in the abdominal area and then they become irritated and trigger the pain you feel and call side stitches. The other belief is that the hunching puts more weight on your diaphragm which causes it to spasm and get tired.
The final theory is dehydration. I’m not going to go into this one. We all know it’s critical to hydrate before, during and after our runs. We know we have to take in electrolytes if we’re running for more than about 60-90 minutes (depending on pace and temperature outside: faster and hotter=more electrolytes).
Bottom line: breath deep with your belly, use rhythmic breathing, pay attention to your posture, and hydrate.