You are out for a run and suddenly out of nowhere you get cramp. It may be a stitch or a cramp in your leg muscle, either way it can put you right off your stride.
So why do cramps happen? Can you prevent them? And how should you deal with them when they do?
Side stitch is a sharp, painful cramp in either the left or right side of the abdomen. There are different theories as to why it happens.
It could be that stitch is caused by fluids that the body finds difficult to digest.
It may be caused by eating too soon before a run. A study of more than 800 people after a community race in Sydney, Australia found those who’d eaten 1-2 hours before exercise were the most likely to get side stitch.
Or another reason could be to do with the flow of blood around the body when you run.
"The theory about stitch is commonly attributed to a blood flow issue," says David James, professor of exercise science at the University of Gloucestershire.
He says: "The blood is redistributed to an active muscle but it’s stolen from other areas and that causes the stitch."
In other words as we run the blood moves away from our diaphragm to our legs and arms. The diaphragm is the main muscle we use for breathing so the pain is caused by a reduction of blood supply to the diaphragm causing it to cramp.
Running coach Karen Weir says: "Not having a strong enough core and slightly leaning to one side when you run or having a poor breathing technique may also contribute to side cramps."
Can you prevent side cramps?
You can try to minimise them by not eating shortly before going on a run and by concentrating on getting a good breathing rhythm going.
If you do get it you can run it off within a few minutes. It may help to stop running and touch your toes, bend forward at the waist and carry on running slowly or rub the area that hurts to help relieve the pain.
"It also helps to focus on deep breathing if you do get it," says Karen.
Scientists have many theories about the cause of muscle cramps but as they are spontaneous it’s hard to offer a definitive reason for them.
"The jury’s still out on the cause of muscle cramps," says Karen who has the RunWithKaren website. "But dehydration, overuse, overloading in a fatigued state and poor technique could be to blame."
Dehydration and loss of sodium is a popular theory: "Some sports drinks have electrolytes within them which may help," says Professor James. "But there’s no definitive research, as it’s all to do with sodium concentration and it’s difficult to manipulate that so you can’t really tell if the drinks are effective."