Although athletic stitch is very common – affecting, for example, an estimated 60% of runners per year – and although references to the problem can be traced back to the works of Shakespeare, there is still no consensus on its cause.

Two alternative causes have been put forward for stitch – recently given the more technical label of ‘exercise related transient abdominal pain’ (ETAP):

• Diaphragmatic ischaemia (impaired blood flow to the diaphragm);
• Stress (from jolting of the torso) on the subdiaphragmatic ligaments supporting the abdominal organs.

However, according to a leading article in the British Journal of Sports Medicine, the former proposition is invalidated by the high prevalence of the complaint among devotees of horse riding, which does not tend to impose high respiratory demands, while the latter is inconsistent with the variability in the site of the pain and the fact that it occurs during swimming.

The article, by Dr DP Morton of Australia, posits a third possible explanation of the problem: irritation (by friction) of the parietal peritoneum, which lines the walls of the abdomen. This, he argues, is sensitive to any torso movement when irritated and, as it extends throughout the abdomen, can give rise to pain in various sites. Furthermore, the subdiaphragmatic portion of the parietal peritoneum is supplied by branches of the phrenic nerve, which arises in the neck, and this would explain the common association of stitch with shoulder tip pain.

As far as prevention/treatment are concerned, Morton makes two suggestions:

• Since energy-dense hypertonic fluids appear to be more provocative of ETAP than isotonic and hypotonic drinks, the former should be avoided as a prevention strategy;
• Since spinal problems may be involved in triggering ETAP, efforts to optimise spinal integrity may be important in its management.

British Journal of Sports Medicine 2003; 37:287-288