It hits you out of nowhere. You’re halfway through a jog, feeling decent, and then—bam. A sharp, stabbing sensation right under your ribs. It feels like someone is twisting a knife into your torso. You slow down. You lean over. You wonder if your lung is collapsing or if you just aren't as fit as you thought you were.
But honestly? Even Olympic athletes deal with this.
What causes side stitches—or what doctors call Exercise-Related Transient Abdominal Pain (ETAP)—isn’t actually a single "gotcha" moment. For years, people blamed a lack of oxygen to the diaphragm. They thought your body was literally suffocating your breathing muscles. That's mostly been debunked. We’ve moved on to better theories, though the medical community is still debating the finer points.
If you've ever had to limp back home because of a cramp, you know how frustrating the lack of a "quick fix" can be. It’s localized. It’s intense. And it usually happens on the right side.
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The Friction Theory: It's Probably Your Peritoneum
Most modern sports scientists, like Dr. Darren Morton who has published extensively on the topic, lean toward the peritoneal irritation theory.
Think of your abdomen as a bag. Inside that bag, your organs are wrapped in a two-layered membrane called the peritoneum. There’s a bit of fluid between these layers so your guts can slide around while you move. When you run, your stomach is full or you're dehydrated, that fluid might get sticky or thin out.
The layers rub together.
This friction creates that sharp, localized "stitch" feeling. It explains why the pain is so specific. It’s not a muscle cramp in the traditional sense; it's more like a localized "chafing" on the inside of your belly wall. This also explains why swimming or running triggers it more than cycling. On a bike, your torso stays relatively still. When you run, you’re bouncing. That vertical displacement jiggles the organs, putting more stress on those membranes.
What You Ate Actually Matters
You’ve probably heard you shouldn't eat before a workout. That’s old news, but the why is interesting. It isn't just about weight in your stomach.
High-osmolar beverages are the biggest culprits. Basically, drinks with a ton of sugar—think heavy fruit juices or full-sugar sodas—pull water out of the interstitial spaces and into the gut. This changes the pressure in your midsection. Research has shown that drinking these types of liquids right before exercise is a near-guaranteed way to trigger a stitch.
Water is usually fine. Most sports drinks are designed to be "isotonic," meaning they match your body's chemistry well enough to avoid this fluid shift. But that apple juice you chugged? It’s likely why your ribs feel like they’re being poked with a hot needle ten minutes into your workout.
The Posture Connection
Strange as it sounds, your back might be the problem.
Physiotherapists have noticed a strong correlation between kyphosis (an increased curve of the upper back) and the frequency of side stitches. If you slouch while you run, you’re compressing the abdominal cavity. This creates extra pressure.
It’s also possible the pain isn't in the abdomen at all. Some evidence suggests the pain is "referred" from the spine. If the nerves in your mid-back are being pinched or irritated by the repetitive jarring of running, your brain might interpret that signal as a sharp pain in your side.
Check your form. Are you hunching over as you get tired? If your shoulders are up by your ears, you’re asking for trouble.
Why Does It Usually Happen on the Right Side?
It’s a classic pattern. Most people report the pain on the right side of the upper abdomen.
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The leading thought here involves the liver. It’s your heaviest organ, and it’s tucked right under the ribs on the right. As you run and breathe, your diaphragm moves up and down. Simultaneously, your liver is bouncing. If you exhale every time your right foot hits the ground, the diaphragm moves up while the liver moves down.
They tug on the ligaments.
This mechanical "tug-of-war" can cause significant strain. It’s a literal internal stretching of the connective tissue. If you find yourself stuck in a rhythmic breathing pattern that always syncs your exhale with your right foot strike, try switching it up. Exhale on the left. It sounds like bro-science, but there is legitimate mechanical logic behind shifting that internal load.
The Mystery of the "Full Stomach"
We know that a full stomach increases the risk, but it’s not just about the weight of the food.
When your stomach is distended, it pushes against that peritoneal lining we talked about earlier. There’s less "sliding room." Everything becomes tighter. This is why even a small amount of food—if it’s the wrong kind—can be worse than a large amount of easily digestible food.
Interestingly, younger people get stitches way more often than older adults. Some researchers think this is because the surface area of the peritoneum changes as we age, or perhaps we just get better at regulating our breathing and movement over time. Or maybe we just stop sprinting everywhere. Either way, if you’re over 40, you might notice these happening less frequently, which is a rare perk of getting older.
How to Stop the Stabbing Mid-Run
If the pain has already started, don't just "tough it out." That usually makes the muscle guarding worse.
- The Reach and Lean: Raise the arm on the side of the pain and lean your torso away from it. This stretches out the intercostal muscles and relieves some of the pressure on the abdominal cavity.
- The "Pursed Lip" Trick: Take a deep breath in, then blow it out through pursed lips like you’re blowing through a straw. This creates back-pressure in your lungs, which can help stabilize the diaphragm.
- The Manual Push: This is what most people do instinctively. Press your fingers firmly into the painful area while you exhale. It seems to help "reset" the tension in the area, though we aren't 100% sure why it works. It just does.
- Change Your Gait: If you’re a heavy heel striker, the jarring is worse. Try to land softer or shorten your stride until the pain subsides.
Myths That Won't Die
We need to stop saying it's a lack of salt.
While electrolytes are important for long-distance performance, there is almost zero evidence that a side stitch is caused by a sodium or potassium deficiency. That’s a "heat cramp" issue, which is entirely different. You can't just eat a banana and expect a side stitch to vanish instantly.
Also, it isn't "the spleen dumping blood." That’s an old-school theory that has mostly been tossed in the bin. While the spleen can contract to move red blood cells during intense exercise, it doesn't align with the specific, sharp pain of ETAP.
Actionable Steps for Your Next Workout
To actually prevent this from happening, you need a system. It’s not just luck.
- Time your pre-run meal: Stop eating solid food at least two hours before a hard effort. If you’re sensitive, make it three.
- Avoid "heavy" fluids: Stick to water or low-sugar electrolyte tabs. Save the orange juice for after the finish line.
- Strengthen your "deep" core: This isn't about six-pack abs. Work on your transversus abdominis and your obliques. A stable trunk moves less, which means less friction for your internal organs.
- Practice 2:3 breathing: Inhale for two steps, exhale for three. This ensures you aren't always exhaling on the same foot strike, which balances the mechanical stress on your internal ligaments.
- Warm up properly: A sudden spike in heart rate and breathing can catch the diaphragm off guard. Gradually increasing your intensity allows the "fluid" in your abdomen to lubricate the membranes properly.
If you’re consistently getting side stitches even during light walks, it’s worth mentioning to a doctor. While rare, constant abdominal pain during movement can sometimes point to other issues like exercise-induced asthma or even gallbladder problems. But for 99% of us, it’s just a matter of friction, fluids, and how we breathe.
Pay attention to your body’s signals. If you feel that slight "twinge" before it becomes a full-blown stitch, slow your pace and focus on deep, belly-focused breathing. Catching it early is the best way to keep your run from turning into a miserable walk back to the car.
Immediate Next Steps
- Audit your pre-workout drink: Check the sugar content of your go-to beverage. If it’s over 6-8% carbohydrate concentration, try diluting it with water next time.
- Check your posture in a mirror: If you have a noticeable "slouch," incorporate face pulls or "Y-T-W" exercises into your gym routine to open up your chest and take pressure off your abdomen.
- Test your breathing: On your next walk, try to consciously exhale only when your left foot hits the ground and see if you notice a difference in how your core feels.