Side stitches, also known as exercise-related transient abdominal pain (ETAP), is a sharp pain felt during or after strenuous activity. The pain is caused by the serratus anterior, a large muscle that extends from the side of the rib cage to the shoulder blade. When this muscle contracts, it pulls on the diaphragm, which can cause the sharp pain known as a side stitch. This type of pain is most common in runners, but can also be experienced by cyclists, swimmers, and other athletes. side stitches are generally not serious and will go away on their own after a few minutes of rest. However, if the pain is severe or does not go away, it may be a sign of a more serious problem and should be evaluated by a doctor. If it’s more of a pain between your shoulders, read this.