Why do you get a stitch in your side?

You know the feeling: you’re running, cycling, or doing some other physical activity, and suddenly you feel a sharp pain in your side, just below your chest. It’s like someone is stabbing you with a needle, and it makes you want to stop and catch your breath. Although there is no precise definition of exactly what a stitch is, everyone knows how to recognise it.

This pain, which often prevents you from breathing, walking or running properly, disappears a few minutes after you stop exerting yourself. And while it can be a little frightening, it is c...