Subtitles section Play video Print subtitles You're running, here in the last quarter of the marathon. You're a beast! You're a champion! You are incredible! But then, suddenly, you feel this sharp pain in your side. It seems to get worse and worse with every breath. It is an attack of the side stitch! And now you have to stop running for a while so it goes away. But don't worry, you are not alone. A study in the year 2000 found that 69% of runners had experienced a stitch, otherwise known as an exercise-related transient abdominal pain, in the last year. And people who exercised in other ways, like swimming or bike riding, also reported having gotten a stitch. But even though they're so common, researchers aren't really sure where the pain comes from. Remarkable that we don't know these things, even about our own bodies⏤one possibility is that it's all about your diaphragm, the domed-shaped muscle between your chest and abdomen. When your diaphragm contracts, your lungs expand and fill with air. When your diaphragm expands, your lungs get smaller and the air is forced back out. But when you exercise, you might be overextending that muscle. When you're running, for example, your foot consistently hits the pavement at the same time as you exhale. When your diaphragm is at its highest and tightest, it might strain the diaphragm, causing it to spasm. It could also be that forceful movement, like the up-and-down motion of running, bounces your internal organs around, straining the ligaments trying to keep them from sliding around inside you⏤which is a really gross thought. The most likely explanation seems to point to the peritoneum, a two-layered membrane that lines the abdominal wall and helps support your organs. Now, normally, there's fluid in between the layers that make sure they don't scrape together too much. Because when they do, you end up with that sharp pain. When you eat a large meal, your stomach pushes out on the inner layer, and when you are dehydrated, like if you've been sweating a lot from exercising, there's less fluid between the layers. The way your body is moving around might bump the layers against each other, too. So, how do you make the pain go away? First, just stop exercising for a bit⏤the pain will eventually pass. Unless it doesn't, in which case, go see your doctor, because I'm not a doctor. And if you want to make sure it doesn't happen again, it's probably worth listening to your mom's advice: Wait a little while after a big meal before jumping in the pool or going out for a run. Working to strengthen your core might help, too. That should reduce the movement in your abdomen while you're exercising, meaning less strain on your ligaments and membranes. This way, your internal organs and all the stuff inside your abdominal cavity can stay right where it's supposed to be without causing stitches that might slow you down. Thanks for asking and thanks especially to all of our patrons on Patreon who keep these answers coming. If you would like to submit questions to be answered, and get these Quick Questions a few days before everybody else, you can go to patreon.com/scishow. And don't forget to go to youtube.com/scishow and subscribe!