It took years for the medical community to finally discover what causes a lateral suture. Suddenly, a runner develops pain in the upper right part of the abdomen, just below the ribs in the front. With each step the pain worsens. Doctors came up with all kinds of explanations for the side stitch and most of it was nonsense.
A side stitch is not caused by gas in the colon because it is not revived by expelling gas. It is not caused by a liver swollen with blood during running, because the liver has a very compliant capsule and does not enlarge very much during exercise. It is not caused by cramps in the muscles of the abdomen because the muscles of the abdomen do not remain rigid when a suture is applied to the side and it does not hurt when pressing the muscles of the abdomen. Lack of oxygen to the diaphragm does not cause them because blood flow to the diaphragm is not interrupted by running. They are not caused by gas trapped in the lungs because gas is not trapped in the lungs during exercise.
The first reasonable explanation and successful treatment came from Dr. Tim Noakes. Thick fibrous bands called ligaments run down from your diaphragm to hold your liver in place. When you run, your liver goes down at the exact moment your diaphragm goes up, stretching the ligaments and causing pain.
Humans have a fixed breathing pattern when they run. They have a breathing ratio of two to one, and they breathe once for every two strides. Most people exhale when the right foot hits the ground. When you breathe out, your diaphragm goes up and, at the same time, the force of your foot strike causes your liver to go down. This stretches the ligaments that attach your liver to your diaphragm, causing pain. So the cause of a lateral suture during intense running is a stretch of the ligaments that hold the liver to the diaphragm and the cure is to relieve the stretch of the ligaments.
When you get a side stitch, stop running and press your hand deep into your liver to lift it up against your diaphragm. At the same time, purse your lips and blow against tight lips as hard as you can. Pushing the liver up stops stretching the ligaments. When you exhale forcefully, your lungs are emptied. The pain is usually relieved immediately, and you can resume running as soon as the pain is gone.