Why You Get Side Stitches (And How to Actually Stop One)

That sharp, stabbing pain under your ribs mid-run has a name: exercise-related transient abdominal pain, or ETAP. Most runners just call it a side stitch, and it's annoying but harmless.

The leading theory is that it's a spasm in your diaphragm — the muscle doing the heavy lifting on every breath — or irritation of the tissue lining your abdominal organs, tugged on by the repetitive bouncing of running. What makes it worse: a full stomach. Eating a real meal too close to your run gives your stomach something heavy to slosh around and pull on that diaphragm/peritoneum connection. Sugary drinks and sports drinks are also flagged as triggers, likely because concentrated sugar solutions (hypertonic fluids) sit in the gut and draw water in, adding bulk and osmotic stress right when you're bouncing around.

The fix is mostly prevention. Give yourself roughly two hours after a full meal before running. Skip juice, soda, and sports drinks in the 30-60 minutes before an easy run — plain water is fine, and you don't need carbs for anything under an hour anyway. Warming up gradually instead of sprinting off the couch also seems to help, since it eases your body into the breathing pattern instead of shocking it.

If a stitch hits anyway, it's not dangerous — it's just uncomfortable. Slow your pace, breathe out hard and sharp right as the foot opposite the pain lands (so if it's on your right side, exhale hard when your left foot strikes), and press your fingers into the sore spot. Some runners also get relief stretching the arm on the same side overhead. Give it a minute or two and it almost always fades.

Stitches are common in new runners and tend to happen less as your core and breathing mechanics adapt to the sport — so don't read one as a sign something's wrong.