A side stitch is almost certainly irritation of the lining of your abdominal wall, not your diaphragm running out of blood. It is extremely common — 69% of runners reported one in the past year — and while it is not dangerous in itself, it is not trivial either: in one event survey 42% of affected runners said it hurt their performance. The most reliable fixes are slowing down, breathing deeply, pressing on the spot, and not eating or drinking much in the two hours before you run.
How common is it?
In a survey of 965 regular sporting participants, the proportion reporting exercise-related transient abdominal pain in the previous year was:
- Swimming — 75%
- Running — 69%
- Horse riding — 62%
- Aerobics — 52%
- Basketball — 47%
- Cycling — 32%
In a single community running event with 848 participants, 27% got one during the race. So if you get side stitches, you are in the majority, not the minority.
Notice the pattern: the sports at the top involve repetitive torso movement — vertical translation or rotation — and cycling, where the torso is relatively still, is at the bottom. That is a clue about the mechanism.
What causes a side stitch?
The explanation most people have heard — that the diaphragm is being starved of blood — does not hold up well. The current best explanation, from the researchers who have done most of the work on this, is irritation of the parietal peritoneum: the membrane lining the inside of your abdominal wall rubbing against the layer covering the organs, made worse by a full or distended stomach.
Their own conclusion is appropriately careful: irritation of the parietal peritoneum best explains the features of the condition, however, further investigations are required. This is a well-supported hypothesis, not a settled fact.
It also explains why the pain is usually along the lower edge of the ribs on one side, why it can refer to the shoulder tip, and why drinking a large hypertonic sports drink right before a run is such a reliable way to produce one.
What actually stops a side stitch?
Among roughly 600 sufferers asked what relieved it:
- Deep breathing — 40%
- Local pressure on the spot — 31%
- Stretching — 22%
- Bending forward — 18%
The authors add the unglamorous truth: the most effective strategy for relieving it remains to stop exercising. Slowing to a walk works. It is not a failure.
How do you prevent side stitches?
- Avoid large volumes of food and drink for at least two hours before running, particularly concentrated drinks — juice, full-strength sports drinks, anything hypertonic. This is the single best-supported prevention.
- Sip rather than gulp during a run.
- Work on thoracic posture and core strength. Both are suggested by the mechanism; neither has strong trial evidence behind it.
- Warm up properly. Stitches cluster in the early minutes of hard efforts.
When it is not a stitch
A stitch comes on during exercise, sits near the rib margin, and goes when you stop. Get abdominal pain checked if it is severe, persists after you stop, wakes you, comes with fever, vomiting or blood, or is in the lower right abdomen. That is a medical question, not a running one.
References
Morton D, Callister R. Exercise-related transient abdominal pain (ETAP). Sports Med, 2015;45(1):23–35. · Morton DP, Callister R. Characteristics and etiology of exercise-related transient abdominal pain. Med Sci Sports Exerc, 2000.