Cramp. It’s a runner’s worst nightmare. One minute you are running along feeling great, next minute you are clutching your leg trying to find a way to relieve the cramp that has taken hold of your calf or hamstring. If this happened at the finish line it wouldn’t be such a problem, but when it happens with 30k or more to go it becomes a big problem. I have either been lucky or well trained as it has never affected me in a race. But when I talk to other runners i realise it is a very common problem and there are a lot of different ideas as to the causes and remedies for it. Some of these have been shown to be scientifically incorrect. There is however one theory which seems to fit the evidence and we can use this, combined with some common findings on who suffers cramp, to outline some prevention strategies and remedies if cramp strikes.