That sharp, stabbing pain in your side during a run is almost certainly a side stitch, formally known as exercise-related transient abdominal pain (ETAP). It’s one of the most common complaints among runners, and while it’s rarely dangerous, it can stop a good run in its tracks. The pain typically hits just below the ribs, more often on the right side than the left, and ranges from a dull ache to a sharp, cramping sensation.
Despite how common side stitches are, researchers still debate exactly what causes them. But we know enough about the triggers, relief techniques, and prevention strategies to help you run through fewer of them.
What Actually Causes a Side Stitch
There’s no single confirmed cause, but several leading theories explain what’s happening inside your body. The most widely supported explanation involves irritation of the peritoneum, the membrane lining your abdominal cavity. When your stomach is full of food or fluid, it gets heavier and tugs on the ligaments connecting your organs to your diaphragm. The repetitive jostling of running amplifies this effect, creating friction and irritation that registers as sharp pain.
Other proposed mechanisms include reduced blood flow to the diaphragm during intense exercise, spasms of the respiratory muscles, and vibration of internal organs with each footstrike. These likely work together rather than in isolation. A full stomach increases the mass bouncing around inside your abdomen, while shallow breathing limits blood flow to the muscles involved in respiration. The result is that familiar knife-like stab under your ribs.
Why It Happens More on the Right Side
Most runners report side stitches on the right side of the abdomen. One likely reason is anatomy: the liver, your heaviest internal organ, sits on the right side. Its weight creates more downward pull on the ligaments connecting to the diaphragm, especially during the impact phase of running. There’s also an interesting postural connection. Right-handed people tend to have a slight rightward curve in their upper spine, and researchers have found that manual pressure on the thoracic spine can reproduce the exact symptoms of a side stitch in people prone to them.
What You Ate and Drank Matters
What’s in your stomach before a run is one of the strongest predictors of whether you’ll get a stitch. Eating a large meal too close to your run is a classic trigger. The Mayo Clinic recommends waiting at least three to four hours after a full meal, or one to three hours after a small snack, before exercising.
Beverages are just as important, and the type of drink matters more than the volume alone. Drinks with high sugar and electrolyte concentrations (hypertonic beverages like fruit juice or some sports drinks) are more likely to provoke a stitch than plain water. These concentrated fluids slow gastric emptying, meaning they sit in your stomach longer and add to the mass pulling on your abdominal ligaments. The higher the concentration of carbohydrates in the drink, the worse the symptoms tend to be. If you need to hydrate before a run, water or a low-sugar electrolyte drink is a safer bet than a sugary sports beverage.
Your Posture Plays a Role
A study published in the Journal of Science and Medicine in Sport found that runners with increased upper-back rounding (thoracic kyphosis) were significantly more likely to experience side stitches. Among those already prone to stitches, the degree of spinal curvature influenced how severe the pain was. This connection makes sense when you consider that posture affects how much tension the peritoneal ligaments are under and how efficiently the diaphragm can move.
Earlier research on children found the same pattern and showed that improving posture led to fewer stitch episodes. If you tend to hunch forward when you run, especially as you fatigue, this could be contributing to recurring pain.
How to Stop a Stitch Mid-Run
You don’t always have to stop completely. These techniques can relieve the pain while keeping you moving:
- Slow your pace. Dropping from a run to a jog, or even a brisk walk, lets the muscles around your ribcage relax and reduces the jarring impact on your organs.
- Breathe deeply and deliberately. Inhale slowly for a few seconds, then exhale fully. Repeat several times. This helps release tension in the diaphragm and the muscles between your ribs.
- Press into the pain. Use two or three fingers to push firmly but gently into the spot where the stitch is sharpest. Bend your torso slightly forward at the same time. Many runners find this provides near-immediate relief.
- Stretch the affected side. Raise the arm on the side of the stitch above your head, then lean gently away from the pain. This stretches the cramping muscles along your ribcage and can break the spasm.
Most stitches resolve within a few minutes using a combination of these techniques. If slowing down and breathing deeply doesn’t help within five minutes, walking until the pain fully passes is the safest approach before picking the pace back up.
How to Prevent Side Stitches
The runners who rarely get stitches tend to share a few habits. First, they time their meals well, giving solid food at least two hours to clear the stomach before running. Second, they warm up gradually rather than launching into a hard pace, which allows the diaphragm and abdominal muscles to adapt to the demands of running.
Strengthening your core, particularly the deep stabilizing muscles of your abdomen, can reduce the frequency of stitches over time. A strong core better supports your internal organs during impact and helps maintain upright posture as you fatigue. Planks, dead bugs, and other exercises targeting deep abdominal stability are more useful here than sit-ups or crunches.
Paying attention to your running posture also helps. Keep your chest open and your shoulders back rather than collapsing forward. This is especially important in the later miles of a long run, when fatigue naturally pulls your upper body into a rounded position.
Finally, practice your hydration strategy during training, not just on race day. If a particular sports drink consistently gives you stitches, switch to water or a lower-carbohydrate option. Your gut adapts to what you train with, so experimenting during easy runs lets you find what works without ruining a workout.
When Side Pain Isn’t a Stitch
A typical side stitch is temporary, tied to exercise, and resolves within minutes of slowing down. But not all abdominal pain during running fits that description. Pain that persists long after you’ve stopped, comes with fever, nausea, or vomiting, or feels different from your usual stitch warrants attention. Severe pain accompanied by chest pressure, bloody stools, or abdominal swelling needs urgent medical evaluation.
Persistent pain isolated to the lower right abdomen could signal appendicitis. Pain under the left ribcage that doesn’t resolve could, in rare cases, involve the spleen. And recurring side pain that shows up even when you haven’t eaten or drunk anything unusual may point to a musculoskeletal issue in the ribs or thoracic spine rather than a true stitch. If your pain doesn’t follow the typical stitch pattern of appearing during exertion and disappearing shortly after, it’s worth getting checked out.