The Scientist: Brian Hoke, a sports physical therapist in Virginia Beach and consultant to Vionic shoesThe Answer:  The technical term is exercise-related transient abdominal pain (ETAP), but you probably know it as that cramp you get in your side when you run, or a “side stitch.” There isn’t a single accepted explanation for why we get them, but we know a few things. One, that they’re super common and even seasoned runners suffer (one in five racers gets them). They’re also, for some reason, more common in women than men and twice as likely to occur on the right side. In any case, they’re not serious and tend to last a few minutes at most.Side stitches can occur while cycling, swimming, aerobics, dancing and even horseback riding. But what is it about running that makes it such a thing? In running, there are two main forces at play: impact and counter-rotation. A runner typically hits the ground with a force that is three times her body weight. Most of that shock is taken in the legs, but some of it travels upward into the trunk. Meanwhile, the shoulders and pelvis rotate in opposite directions (right leg forward, left arm forward), which twists the muscles surrounding the abdomen.


This helps explain two of the main theories behind ETAP. Some think that the ligaments that hold our internal organs together are getting tugged on as we run, causing pain, or that the soft membrane that lines the abdominal cavity (the peritoneum) is being irritated. The third hypothesis is that the diaphragm is not getting enough oxygen—since running requires a whole lot—and so it begins to tighten up, or spasm.When you feel a side stitch coming on, slow down a little, lean forward and place your hands on your belly where you feel the pain. Press inward and upward and hold the pressure for about 10 seconds. This may provide enough support to allow the muscle spasm to relax. Purse your lips (like you were going to give someone a kiss) and breathe slowly, trying to exhale more completely with each breath. If the pain becomes unbearable, stop running and walk. It may also help to place your hands over your head and gently rotate your trunk a few times. You can also relax the muscles of the abdomen by lying down and pulling your bent knees up to your chest.If the feeling lasts 10 minutes or more, it might not be a stitch; it could be appendicitis or a swollen spleen.MORE: How Your Period Affects Running