Side cramps during running, often called “stitches,” are sharp, localized pains that strike along the lower edge of your ribcage, most often on the right side. About 80% of the time, the pain is concentrated in one specific spot rather than spread across your abdomen. They’re one of the most common complaints among runners of all levels, and while they’re harmless, they can completely derail a run.
What’s Actually Happening in Your Body
Researchers have debated the cause for decades, and three leading theories have emerged: reduced blood flow to the diaphragm, stress on the ligaments that connect your abdominal organs to your diaphragm, and irritation of the parietal peritoneum, the membrane lining the inside of your abdominal wall.
The peritoneal irritation theory has gained the most traction in recent years. Your abdominal organs sit inside a double-layered membrane, and between those layers is a thin film of fluid that allows them to glide smoothly. During running, the repetitive jarring motion, combined with changes in abdominal pressure from heavy breathing, may increase friction between these layers. That friction triggers a sharp, stabbing pain right along the lower border of your ribs. The pain is “transient,” meaning it resolves once you stop or slow down, which is why the medical term is exercise-related transient abdominal pain (ETAP).
Why Running Triggers It More Than Other Exercise
Running involves a unique combination of vertical jolting and rhythmic torso rotation that puts more mechanical stress on your abdominal cavity than cycling, swimming, or weight training. Each foot strike sends a small shock wave upward through your torso, tugging on the ligaments that suspend your liver, stomach, and spleen. At the same time, your diaphragm is working hard to keep up with your breathing demands. This collision of forces makes running one of the most reliable triggers for stitches.
Downhill running is particularly provocative. The combination of torso hyperextension (leaning back slightly to control your descent) and increased impact force with each stride amplifies the mechanical stress on your abdomen and spine.
Eating and Drinking Before a Run
What and when you eat before running is one of the strongest controllable risk factors. A full stomach increases the weight pulling on your abdominal ligaments and changes how your peritoneal membranes interact. High-sugar drinks like fruit juice are especially problematic because their high concentration draws fluid into the gut, increasing abdominal volume and pressure.
The standard recommendation is to avoid large meals for two to three hours before running. Small, low-fiber, low-fat snacks are less likely to cause issues if you need fuel closer to your run. Water is a safer choice than sugary or concentrated sports drinks in the hour before you head out.
Your Posture Plays a Bigger Role Than You’d Think
This is the factor most runners overlook. Research involving postural assessments of over 150 subjects confirmed that increased thoracic kyphosis, a rounded upper back, is associated with more frequent stitches. The connection makes anatomical sense: the intercostal nerves that supply sensation to your anterior abdomen originate from the thoracic spine. When the mid-back is stiff, misaligned, or excessively curved, those nerves may become more easily irritated during the repetitive motion of running.
A published case study of an elite runner illustrates this vividly. After a trampoline injury that caused stiffness at the T7-T8 vertebral level, the runner developed severe, recurring stitches. Targeted treatment to restore spinal mobility resolved the problem. Earlier clinical observations found that improving posture in children who suffered frequent stitches reduced their symptoms as well.
If you spend your workday hunched over a desk and then go straight to a run, your mid-back is already in a compromised position. Thoracic mobility exercises, like foam rolling your upper back or doing seated rotations, may help reduce your risk over time.
Age and Fitness Level
Side stitches become less frequent, less severe, and less common as you get older. Younger runners report them significantly more often, though researchers aren’t entirely sure why. One possibility is that the peritoneal membranes become less sensitive with age, or that older runners have simply adapted their pacing and breathing patterns over years of experience.
Here’s something that surprises many people: fitness level doesn’t protect you the way you’d expect. Athletes at all levels are equally susceptible to stitches. An elite marathoner can get one just as easily as a beginner. However, training more frequently does reduce how often stitches occur. So consistency helps, even if raw fitness doesn’t make you immune. The severity of the pain, when it does strike, is roughly the same regardless of how fit you are.
How to Stop a Stitch Mid-Run
When a stitch hits, you have a few reliable options. The first is to slow your pace and focus on deep, controlled breathing. Pursed-lip breathing, where you exhale as if blowing out birthday candles, helps regulate diaphragmatic pressure and can ease the pain within a minute or two. Some runners find that exhaling forcefully when the foot opposite to the painful side strikes the ground helps break the cycle of irritation.
Pressing your fingers firmly into the painful spot while bending slightly forward at the waist is another common technique that provides relief for many runners. If the pain persists after a minute of these strategies, stop running and walk while continuing to breathe deeply. Most stitches resolve within a few minutes of walking.
Reducing Your Risk Over Time
Prevention comes down to a handful of practical changes:
- Time your meals. Keep a two-to-three-hour gap between eating and running. Avoid concentrated, sugary drinks close to exercise.
- Warm up gradually. Starting a run at full pace is a classic stitch trigger. Spending five to ten minutes at an easy pace lets your diaphragm and abdominal structures adjust to the demands of running.
- Work on thoracic mobility. Foam rolling, cat-cow stretches, and thoracic rotation exercises can reduce the spinal stiffness linked to recurring stitches.
- Strengthen your core. Supporting your abdominal organs with stronger deep core muscles reduces the mechanical load on your peritoneal ligaments. A supportive broad belt can serve a similar function for runners who get stitches frequently.
- Build running frequency. Training more often, even at easy intensities, is one of the clearest ways to reduce how frequently stitches occur.
Side stitches are one of running’s most universal annoyances, but they’re a mechanical and pressure-related problem with practical solutions. Most runners who address their pre-run nutrition, breathing habits, and posture see a noticeable drop in how often they deal with them.