Why do you get a stitch when running? The evidence on the runner's side ache

The sharp pain that ambushes runners under the ribs has a clinical name — exercise-related transient abdominal pain, or ETAP — and a research literature going back decades [s1]. It is extraordinarily common: roughly 70% of runners report it in the past year, and in a single running event about one in five participants can expect to feel it [s1]. It is also harmless and self-limiting. What causes it is less settled than the folklore suggests: the best current explanation is not trapped wind, a starved diaphragm, or a cramping muscle [s1].

What the stitch actually is

ETAP is most prevalent in activities involving repetitive torso movement with the torso extended — running above all, and horse riding [s1]. The pain sits typically in the lateral mid-abdomen along the lower rib margin, and can refer to the tip of the shoulder, tissue supplied by the same phrenic nerve [s1]. In a survey of 848 people finishing the 14 km Sydney City to Surf run, sufferers most often placed it in the right (46%) or left lumbar (23%) region of the abdomen, and 88% described it as well-localised [s2].

It is not a beginner's complaint that trained bodies outgrow entirely. It is most common in the young: its prevalence fell with age in the City to Surf survey (r = -0.23, p < 0.01) and in a separate survey of 965 participants across six sports (r = -0.28, p < 0.01), and in both it was unrelated to sex or body mass index [s2][s3]. Running is the worst offender by a wide margin: in that six-sport survey, ETAP was 10.5 times more common in running and 9 times more common in horse riding than in cycling, and referred shoulder-tip pain was 13 times more common in running than cycling [s3]. Well-trained athletes are not immune, but they report it less often, and people who train more frequently experience it less [s1][s3]. It is not trivial either: 42% of City to Surf sufferers said the pain was detrimental to their performance [s2].

Why it happens — and why the usual stories fall short

Researchers have floated several mechanisms: ischaemia of the diaphragm, stress on the ligaments that suspend the abdominal organs, gastrointestinal ischaemia or distension, cramping of the abdominal muscles, compression of the celiac artery, aggravation of the spinal nerves, and irritation of the parietal peritoneum — the sensitive inner lining of the abdominal wall [s1]. Of these, the review concludes that irritation of the parietal peritoneum best explains the features of ETAP, though it stresses the question is not fully resolved [s1].

The food connection is the strongest practical clue, and it fits that lining theory. ETAP is made worse by the postprandial state, and concentrated, hypertonic drinks are particularly provocative [s1]. In the City to Surf survey, runners who had eaten a large mass of food relative to their body weight in the one to two hours before the event were more likely to develop the stitch — while the nutritional content of the meal made no difference [s2]. A full, heavy stomach tugging on the peritoneum, rather than what was on the plate, appears to be the trigger.

What actually helps

Because the cause is still being pinned down, prevention advice rests largely on observation, but it is consistent [s1]. The main strategies are to avoid large volumes of food and drink for at least two hours before exercise — especially concentrated, sugary or hypertonic beverages — to improve posture, particularly through the thoracic spine, and to support the abdominal organs by building core strength or wearing a broad supportive belt [s1]. Techniques for banishing a stitch once it strikes mid-run are more equivocal; the familiar tricks of bending forward, tensing the abdomen or breathing deeply are anecdotal rather than proven [s1].

The honest summary is that the runner's stitch is common, benign and self-resolving, most likely a mechanical irritation of the abdominal lining rather than anything wrong with the muscles, gut or diaphragm [s1]. If it plagues you, the two levers with the most evidence behind them are timing your last big meal well before you set off and not drinking concentrated sports drinks right before or during a run [s1][s2]. Pain that is severe, persistent, or unrelated to exercise is a different matter and warrants medical attention. This article is informational and not medical advice.

Sources

• Exercise-Related Transient Abdominal Pain (ETAP) — Sports Medicine, 2014-09-03
• Epidemiology of exercise-related transient abdominal pain at the Sydney City to Surf community run — Journal of Science and Medicine in Sport, 2005-06-01
• Factors influencing exercise-related transient abdominal pain — Medicine & Science in Sports & Exercise, 2002-05-01