Georgina Lee, of Avonside Girls High School, asks :-

Rebecca Cadogan, of Clyde, asked:-

What causes stitch? Why do people get the stitch sometimes when they run?

Ross Boswell, a pathologist at the Christchurch Medical School, responded.

The stitch is a pain in the left side which comes on during exercise. It is well-known to all children, but less common in adults.

I can find no reference to it in standard medical textbooks, but I have once read (and since believed) that the pain is caused by contraction of the spleen. The spleen is an organ about the size of a fist that sits in the upper left side of the abdomen, behind the stomach. Its functions include the removal of old worn-out red blood cells, but especially in children it may also be a site of production of new red cells. In some animals the spleen functions as a reservoir of new red cells, and at times of stress it can contract and squeeze them out into circulation to increase the oxygen-carrying capacity of blood. In humans this reservoir function is not very well developed, and the capacity of the splenic reservoir is only about 50mL. This is not really enough to make a noticeable difference in oxygen carriage.

If the pain of the stitch is due to splenic contraction, then there is some basis to the standard treatment I was taught as a child, which is to bend over and touch your toes. This would put some external pressure on the spleen and help it to empty its reservoir, making the pain go away.