What Causes Side Stitches When Running

That sharp, stabbing pain in your side during a run feels like someone is driving a knife into your ribs.

It only happens on one side, makes it hard to breathe, and suddenly running feels impossible.

The good news: side stitches are extremely common and manageable once you understand what’s happening and how to fix it.

About 70% of runners experience a side stitch at some point, which means you’re not alone and there’s plenty of solid research on preventing them.

So, in this article you’re going to learn the research-backed practical advice on:

• What side stitches actually are and why you feel them below your ribs
• Three competing theories on the cause, and what science says about each
• Which foods and drinks you should avoid before running
• Who’s most at risk and why fitness level matters
• How to stop a stitch mid-run when one strikes
• Long-term prevention strategies with proven effectiveness

What Is a Side Stitch?

A side stitch is a sharp, stabbing, or cramping pain that appears just below your ribs, almost always on one side of your body.

Medical researchers call it exercise-related transient abdominal pain (ETAP). The word “transient” means it goes away quickly once you stop running or slow down.

The pain can range from a mild ache to an intense stab that makes you want to stop moving completely.

Sometimes the pain extends to the tip of your shoulder on the same side, a detail that turns out to be important for understanding what causes stitches.

Side stitches typically vanish within minutes of reducing your pace or stopping activity entirely.

Though they’re painful in the moment, they’re not dangerous.

Side stitches don’t indicate an injury or underlying condition.

Newer runners and younger athletes experience stitches more often, but even experienced marathoners can get them, especially if they’re racing hard or have eaten close to run time.

What Causes Side Stitches When Running?

The exact cause of side stitches remains a scientific puzzle. Three main theories dominate the research, and each one is supported by actual evidence.

Understanding these competing ideas helps explain why different prevention strategies work for different runners.

Theory 1: Low Blood Flow to the Diaphragm (Largely Disproven)

For decades, the prevailing explanation was that blood flow drops to your diaphragm during hard running, starving the muscle of oxygen and causing pain.

The logic made sense: when you run hard, your leg muscles demand blood, and the stomach demands blood if you’ve eaten recently, so the diaphragm might be left short.

But evidence has largely dismantled this theory.

In 2006, researchers at Avondale College in Australia tested 28 athletes with a history of side stitches, measuring their breathing and lung function before and after a treadmill run.

Fourteen athletes developed a stitch during the test, and fourteen did not.

When the researchers compared the two groups, they found only a minor decrease in exhalation power in the stitch group but no meaningful difference in inhalation strength.

If blood flow were the culprit, inhalation strength (controlled by the diaphragm) would show obvious weakness during stitch episodes.

That didn’t happen, so ischemia theory fell out of favor.

Additional evidence against this theory: horse riders experience stitches in up to 62% of rides, yet horseback riding demands almost no heavy breathing. Blood flow shouldn’t be an issue.

Theory 2: Organs Pulling on Ligaments and Irritating the Abdominal Lining (Most Supported)

The most widely supported explanation involves the mechanical stress of impact.

Your stomach, liver, and other abdominal organs are anchored to your diaphragm and abdominal wall by connective tissues called visceral ligaments.

Every time your foot strikes the ground while running, your organs bounce downward. The ligaments holding them in place stretch under that weight.

When the strain reaches a tipping point, those stretched ligaments irritate the parietal peritoneum, a sensitive membrane that lines the inside of your abdomen.

That irritation is the pain you feel.

Research has shown that high-sugar fluids increase stitch severity significantly compared to water or sports drinks during exercise.

This theory elegantly explains several confusing aspects of side stitches.

If your stomach is fuller or heavier because you ate a large meal or drank concentrated juice, there’s more weight pulling on those ligaments, making a stitch more likely.

Sugary drinks stay in your stomach longer because they absorb more slowly than water or isotonic sports drinks, meaning the mechanical stress lasts longer.

This also explains why some sports trigger stitches far more than others. Running and horseback riding involve vertical jolting that yanks organs downward, while swimming involves rotational twisting that stresses the ligaments differently.

Cycling, by contrast, keeps organs relatively stable, which is why cyclists rarely report stitches.

This finding strongly supports the visceral ligament theory over the other two competing explanations.

Theory 3: Irritation of the Upper Spine Nerves (Emerging Evidence)

A third explanation focuses on the thoracic spine, the section of your backbone in the upper back.

In a 2004 clinical report, researchers Morton and Aune found that in 47% of athletes with a history of side stitches, they could reproduce the exact stitch pain by applying manual pressure to specific vertebrae (T8-T12) in the upper back.

This suggests that dysfunction in the thoracic spine, or how the spine moves during running, contributes to ETAP.

The nerve connections support this theory: the phrenic nerve (which controls the diaphragm) and the nerve branch that reaches to your shoulder tip both originate from the same area of the spine.

That’s why some stitches extend pain to your shoulder. It’s referred pain along the same nerve pathway.

Posture matters here too: research has linked kyphosis (excessive forward curvature of the upper back) to an increased risk of stitches, likely because the rounded posture increases stress on the thoracic vertebrae during the vertical impact of running.

However, this theory doesn’t fully explain the strong connection to food and fluid intake, which is more easily explained by the visceral ligament theory.

Does What You Eat and Drink Before Running Cause Side Stitches?

Yes. The research is clear that timing and content of pre-run meals and fluids significantly affect your risk.

A landmark 2004 study had 40 athletes with a history of side stitches consume different fluids before treadmill running: water, sports drinks, fruit juice, or nothing at all.

Fruit juice, with its high concentration of sugar, triggered severe stitches in far more cases than the other options.

Sports drinks (moderate sugar) performed better than juice but worse than plain water.

The mechanism: high-sugar fluids are hypertonic, meaning they pull water into the stomach for dilution rather than absorbing quickly into the bloodstream.

The result is a stomach that stays full and heavy for longer, prolonging the mechanical stress on those visceral ligaments.

Avoid concentrated sugary drinks like fruit juice for 60-90 minutes before running.

Large meals have the same effect whether they’re high-sugar or not. A full stomach weighs more and pulls harder on the ligaments as you run.

Most runners find that waiting 2-3 hours after a substantial meal before running reduces stitch risk dramatically.

If you’re running very early in the morning and need fuel, stick to something small and easily digestible: a banana, a handful of nuts, or a small piece of toast.

Test your pre-run nutrition during training runs, never during a race or important workout.

Who Gets Side Stitches Most Often?

Side stitches are not distributed equally across all runners.

Certain factors predict who’s more vulnerable. The good news is that most of them are changeable.

Age and experience level. Younger, less experienced runners report stitches more frequently than older, well-trained athletes.

Consistent training appears to have a protective effect.

The more you run, the less likely you are to develop stitches, even in the early season.

This suggests that adaptation and conditioning matter, not just age.

Posture and spinal alignment. Runners with excessive upper back curvature (kyphosis) experience stitches more often, likely because the rounded posture increases stress on thoracic vertebrae during running impact.

If you have chronic stitches, check your running posture for excessive forward hunching.

Core strength. A 2014 study of 50 runners found that athletes with stronger abdominal muscles, specifically a larger resting transversus abdominis, reported significantly less pain from ETAP.

Weak core muscles can’t stabilize your torso effectively during running, which increases stress on the diaphragm and overlying ligaments.

Breathing patterns. Shallow breathing or breath-holding during running restricts your diaphragm and can trigger spasm or pain.

Deep, rhythmic breathing (belly breathing) allows the diaphragm to move fully and reduces strain.

How Do You Get Rid of a Side Stitch Mid-Run?

If a stitch catches you during a run, several techniques provide fast relief. Prevention is always preferable to treating a stitch once it starts.

Slow your pace and focus on deep breathing. Reduce to an easy jog or walk and shift to slow, deep belly breathing through pursed lips.

This fully engages your diaphragm and reduces the cramping sensation.

Many runners report relief within 30-60 seconds of breathing this way.

Bend forward while tightening your core. Stop or slow dramatically, then bend at the waist while pulling your abdominal muscles in tight.

This changes the position of your organs and reduces tension on the stretched ligaments.

Relief often comes within 60-90 seconds.

Adjust your running form. Shorten your stride, reduce the impact force, or shift your weight forward slightly to reduce vertical bouncing.

Even a small reduction in impact can diminish stitch intensity.

Apply external pressure or wear compression. Some runners find that a snug belt or compression around the waist provides temporary mechanical support and eases discomfort.

Most stitches resolve within 5 minutes if you slow down and apply one of these techniques.

How Do You Prevent Side Stitches From Coming Back?

Long-term prevention is far more effective than chasing relief during runs.

The strategy has three parts: manage pre-run nutrition, improve breathing and form, and build strength.

Part 1: Pre-Run Nutrition and Hydration

Timing and food choice matter equally.

Avoid solid meals 2-3 hours before running. This gives your digestive system enough time to move food from your stomach into your small intestine, so there’s less weight pulling on ligaments during your run.

For fluids, avoid anything high in sugar 60-90 minutes before running. Skip fruit juice, soda, and heavily sweetened sports drinks.

Water or a low-sugar electrolyte drink is your safest bet for pre-run hydration.

If you run in the early morning and need fuel, eat something small and easily digestible 30-45 minutes before heading out. Consider a banana, a piece of toast with a thin spread of nut butter, or a small handful of almonds.

These options provide energy without sitting heavy in your stomach.

Critical rule: Always test new fueling strategies during easy training runs, not before a race or hard workout.

Your gut’s tolerance changes with pace, intensity, stress level, and individual factors that only your experience will reveal.

Part 2: Breathing and Running Form

How you breathe directly affects diaphragm stress.

Shallow, chest breathing leaves your diaphragm cramped and vulnerable.

Instead, practice belly breathing: allow your abdomen to expand when you inhale, drawing air deep into your lungs.

Start this practice during easy runs when you’re relaxed, not during hard efforts when you’re already stressed.

Once belly breathing feels natural, maintain it during all your runs, especially during speed work.

This single change eliminates stitches for many runners.

Your running posture also matters. Aim for an upright torso with your shoulders back, not hunched forward.

Forward slouching compresses your abdomen and restricts diaphragm movement, increasing stitch risk.

A brief 5-10 minute warm-up at an easy pace before any hard effort also reduces stitch frequency, likely by giving your digestive system and respiratory system time to settle into a pattern.

Part 3: Core and Spine Strength

Strengthening your core, especially the transverse abdominis (your deepest abdominal muscle), provides the most durable long-term protection against ETAP.

Research shows that runners with stronger trunk muscles and larger resting transversus abdominis experience significantly less ETAP pain.

You don’t need elaborate routines. Ten to 15 minutes of core work, 3 days a week, creates measurable strength gains in 4-6 weeks.

Focus on planks (front and side), dead bugs, bird dogs, and carries (farmer’s carry, suitcase carry).

These exercises build stability without requiring equipment.

If you have chronic stitches or suspect thoracic spine involvement, also include spinal mobility work. Thoracic rotations and gentle extensions help restore movement in the upper back and reduce nerve irritation.

Hip and back strength matter too. Running demands stability from your core, back extensors, and hip muscles as you move through each stride.

When these muscles are weak, compensation patterns emerge, and your diaphragm bears extra load.

A physical therapist can assess whether thoracic spine dysfunction or posture issues are contributing to your stitches and design a targeted program.

If you experience chronic stitches despite trying these strategies, have a physical therapist evaluate your posture and spine mobility.

Kyphosis or disc issues may require hands-on treatment that goes beyond self-directed core work.