Side Stitch While Running: Why It Happens & How to Stop It

A side stitch (properly called exercise-related transient abdominal pain) is a sharp pain along your lower ribs, often on one side and more often the right. Nobody has pinned down the exact cause. The best-supported explanation is irritation of the lining of your abdominal cavity, and a popular theory adds your diaphragm (the breathing muscle beneath your lungs) being tugged in two directions at once by your breathing and your footstrike. The evidence for quick fixes is limited, but to stop one fast, try this: slow to a walk or an easy pace, switch to slow, deep belly breaths instead of shallow chest breathing, press firmly on the spot as you exhale, and if the pain is on your right side, try exhaling as your left foot lands instead of your right. Below: why stitches happen, how to prevent them, how to tell a stitch from something else, and red flags that mean see a doctor.

A stabbing pain under your ribs mid-run is one of the most common complaints I hear from runners at every level, from teenagers chasing a fitness test to lifelong non-runners who've never made it past ten minutes without being stopped cold. I've had my fair share myself, and I've answered this question from readers more times than almost any other, so I'll also show you when the pain isn't a stitch at all.

Why Side Stitches Happen

The exact cause isn't settled, but here's the theory most coaches work from. Your diaphragm — the muscle that does most of the work of breathing — is connected to your liver, spleen and stomach. As you run, all three organs bounce up and down with every stride, pulling on your diaphragm as they go.

Your breathing does the same job in the opposite direction. Breathe out, and your diaphragm rises. Breathe in, and it drops. Most runners unconsciously settle into a fixed pattern, exhaling on the same foot every time.

The trouble starts when your breathing cycle and your footstrike cycle pull your diaphragm in opposite directions at the same moment. Stitches are often felt on the right side, where your liver sits, though they can happen on either side. Do it a few hundred times in a row, and that repeated tension may well be your stitch.

How to Prevent Side Stitches

Prevention beats a mid-run fix every time, and it comes down to three sensible habits.

Practise deep belly breathing on your easy runs, not just when a stitch hits. Slow, deep breaths from your belly rather than shallow ones from your chest, and the pattern becomes automatic long before you need it under harder effort.

Give your stomach time before you run. Avoid eating or drinking a large volume in the one to two hours beforehand, and be especially wary of sugary or concentrated drinks — a full stomach adds physical load onto a diaphragm that's already working hard.

Build a strong core. This is the longer-term fix, and it's the one I'd point you to if stitches keep recurring no matter what else you try. One reader, a teenager who'd avoided running for years because a stitch caught him every single time, got exactly this advice: work on your back, abs and obliques, be patient, and build up gradually rather than chasing a quick trick. It isn't glamorous, and the research is modest, but it's the longer-term fix most often recommended.

On days a stitch tends to show up, it's also worth consciously varying which foot you exhale on — breaking the habitual pattern may be enough on its own.

Is It a Side Stitch, or Something Else?

Most of what lands in my inbox about rib and stomach pain during running is a classic side stitch. A handful of readers describe something that doesn't quite fit, though — and it's worth knowing the difference.

Gas, not breathing. One reader, sixteen and training hard for an army fitness test, found his pain varied wildly — three miles on a good day, half a mile on a bad one. That pattern points more towards trapped gas from diet or swallowed air than a breathing-pattern stitch, and it responds to different fixes: eating more slowly, cutting back on carbonated drinks, and checking for food triggers rather than adjusting your breathing.

Happens even when you're not running, or switches sides. One reader, fourteen, had his cramp start under the right ribs during a school run, then it returned two days later at a theme park, and eventually turned up under both ribs while he was simply walking, not running at all. That's not the classic exertional pattern. A stitch that shows up at rest, or moves between sides, is worth mentioning to a doctor rather than assuming it's the same thing covered on this page.

Only happens in races, never in training. One reader's son, a high-school runner, cramped reliably around the two-to-two-and-a-half-mile mark in races but almost never in training — including a 10-mile Sunday run with no trouble at all. Race-day tension and effort can change your breathing pattern and gut blood flow, and pre-race food and drink often differ from a normal training day too. The exact reason isn't established. If that's you, you're not doing anything wrong in training.

Pain that starts after you've already stopped. Pain that begins once you're done running, rather than during, points more towards diet, hydration or digestion timing than the classic mid-run diaphragm mechanism this page covers — see my digestion and running guidance for that angle.

Pain below the right chest that doesn't fit the pattern at all. If that's you, skip ahead to the red flags section below — this one needs a different answer to the rest of this page.

What you're feeling	Likely cause	What to do
Sharp pain under the right ribs during running, eases with rest	Classic side stitch (exact cause still debated)	Belly breathing, switch exhale foot, build core strength
Pain varies a lot day to day, not clearly tied to breathing	Trapped gas from diet or swallowed air	Eat more slowly, cut carbonated drinks, check food triggers
Happens at rest too, or moves between sides	Atypical pattern	See a doctor
Only happens in races, never in training	Race-day tension and adrenaline	Practise pre-race calming breaths; not a training fault
Starts after you've already stopped running	Diet, hydration or digestion timing	See digestion and running guidance
Genuine chest pain, not clearly under the lower ribs or side	Needs medical assessment	See red flags below — don't self-diagnose

When to See a Doctor (Red Flags)

Most side stitches are entirely benign, and almost all resolve with the steps above. A few patterns deserve a proper check rather than a guess from an article, though.

If what you're describing is genuinely in your chest, rather than clearly under your lower ribs or side, get it checked out by a doctor first — that's my honest, immediate reaction any time chest-area pain comes up, before any explanation of what it might be. I'm not a doctor, and this is a long-distance read of a symptom I can't examine.

The same goes for pain with shortness of breath that's out of proportion to your effort, pain that doesn't ease once you slow down or stop, or pain that happens at rest — which, as covered above, doesn't fit the standard exertional pattern at all.

This isn't a scare tactic. Most side stitches are harmless. But the ones that don't fit the pattern deserve a real check, not a guess — for the fuller picture, it's worth reading up on red-flag symptoms across running injuries.

Recognising when something doesn't fit the pattern is coaching-relevant knowledge. Diagnosing what's actually happening in your body isn't my job. That's always a doctor's call.

Side stitches are frustrating, but for almost everyone they're fixable — breathe from your belly, mind your timing around food, build a strong core, and give it a few weeks to take hold.

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