Science

Why Do You Get a Stitch in Your Side When You Run?

Rive News Research Desk

Published October 30, 2026 · 6 min read

Key takeaways

A side stitch is exercise-related transient abdominal pain, usually sharp and just below the ribs, often on the right side.
The leading theory blames friction between two layers of tissue lining the abdomen, worsened by a full stomach.
About 70 percent of regular runners report one in a year; slowing down and breathing deeply usually ends it within minutes.

A lone jogger running on a paved trail through open grassland

A jogger mid-run. The repeated up-and-down motion of running jostles the torso more than almost any other exercise, which is why stitches strike runners most. Image: Wikimedia Commons

Image Credits: Wikimedia Commons

A side stitch is the sharp, stabbing pain that strikes just below your ribs during a run, most often on the right side. Doctors call it exercise-related transient abdominal pain, or ETAP.

It is one of the most common complaints in running. Around 70 percent of regular runners say they have had one in the past year, according to the sports medicine review summarized on ScienceInsights.

This article explains what a stitch is, walks through the leading scientific theory behind it, covers why some runs trigger one and others do not, and lays out what actually helps when one hits.

What is a side stitch?

A side stitch is a localized pain in the mid-abdomen, usually along the lower edge of the rib cage. When severe it feels sharp or stabbing; when mild it feels like a cramp, ache, or pulling sensation.

The pain most often lands on the right side. It can also come with a stabbing ache at the tip of the shoulder, which is referred pain from tissue served by the phrenic nerve, the nerve that also supplies the diaphragm.

Stitches are not a true injury. They fade within minutes once you ease up, and they are not a sign of anything dangerous in an otherwise healthy runner.

The leading theory: irritated tissue layers

The most widely accepted explanation comes from a study by Morton and Callister, published in Sports Medicine in 2005. Their proposal: a stitch is irritation of the parietal peritoneum, the membrane that lines the inside of the abdominal wall and covers the organs.

Two smooth layers sit against each other inside your abdomen. During repetitive, bouncing movement like running, those layers can rub together. The friction irritates the tissue and produces the sharp, localized pain.

A full stomach makes the rubbing worse. The review on SpringerMedicine notes that stitches are aggravated by the postprandial state, meaning right after eating, and that hypertonic drinks like sugary sports beverages are particularly provocative.

This theory best explains the pattern of the pain. It fits why stitches strike during jostling sports, why they worsen after a meal, and why they fade quickly at rest.

The older theories that lost ground

The stitch was once blamed on the diaphragm running short of blood. The idea was that exercise shunts blood away from the diaphragm toward the leg muscles.

That theory has weakened. During hard exercise both the diaphragm and the leg muscles work harder, so it is unlikely the diaphragm gets starved of blood.

Another old theory blamed the ligaments that suspend the liver and other organs from the diaphragm. The jolting of running was thought to stretch these ligaments until they cramped.

That idea has a hole too: stitches also happen in sports without much jolting, like swimming. The ligament theory cannot explain that.

Surveys of 965 athletes across six sports found that running and horse riding produce stitches far more often than cycling, about 10.5 and 9 times more often respectively, according to research by Morton and Callister summarized on ResearchGate. The common thread is torso movement, which points back to the friction theory.

Two runners mid-stride on a forest trail

Two runners in stride. Deep, rhythmic breathing is the simplest way to ease a stitch when one strikes. Image: Wikimedia Commons

Why some runs trigger one and others do not

Eating too close to the run is the biggest trigger. A stomach full of food or sugary drink sloshes and swells, increasing friction between the tissue layers.

Shallow, rapid breathing raises the risk as well. Short chest breaths keep the diaphragm tense, while deep belly breaths let it move through its full range. The bouncing itself is the key ingredient, much like the sudden forces that make your stomach drop on a roller coaster.

Fitness and age play a role. The athlete surveys found that stitch prevalence and severity both decline with age, and beginners suffer more than trained runners.

Warm-up matters. A gradual warm-up lets your breathing settle into a rhythm before the jostling starts, instead of demanding deep breaths mid-bounce.

What to do when a stitch hits

Slow down first. Dropping to a walk or an easy jog gives the tissue layers a break, and most stitches fade within a few minutes.

Press into the pain. Push your fingers firmly into the sore spot just under the ribs and press upward while you exhale deeply.

Sync your breathing with your stride. Try exhaling when the foot on the opposite side of the pain strikes the ground, which evens out the forces on each side of the torso.

Do not eat a big meal in the two to three hours before a hard run. If you need fuel, keep it small and low in sugar.

Stretching the right side can help too. Raise the arm on the painful side overhead and lean gently to the left to lengthen the tissue along the rib cage.

Frequently asked questions

Why does the stitch hit the right side more often?

The liver sits on the right, just below the rib cage, and it is the heaviest abdominal organ. The classic explanation says its weight stresses the diaphragm more on that side during the bounce of running.

Can a stitch happen while walking or swimming?

Yes, though it is less common. The friction theory fits any activity with repetitive torso movement. Running simply produces the most jostling per minute, which is why it leads the statistics.

Is a side stitch dangerous?

In a healthy person, no. It is transient pain, not damage. But pain that does not fade with rest, or pain paired with dizziness or chest symptoms, deserves a doctor's opinion.

Does drinking water during a run cause stitches?

Plain water in moderate amounts is not the main culprit. The research points more strongly at large volumes and hypertonic sugary drinks, which provoke stitches more than water does.

The bottom line

A side stitch is most likely friction between the tissue layers lining your abdomen, made worse by a full stomach and the bouncing of running. It is common, brief, and not dangerous.

The practical formula is simple: eat light before you run, warm up gradually, breathe deep and rhythmic, and slow down the moment one starts. Within minutes, it is usually gone.

Your next run is the perfect test. Eat two to three hours ahead, skip the sugary drink, and see if the stitch stays away this time.

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Author bio: Rive News is the research desk behind this site's science explainers. We read the studies so your run goes smoother.

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Taggedrunningside stitchexercise painsports medicineETAP