If there is one thing every runner dreads for its devastating potential to reduce winners to also-rans and silver medals to bronze, it's cramp. So everybody has their favourite cramp theory and their favoured remedy but lets consider some facts first. Onset of cramp is usually after 30km in a distance race, regardless of running speed. Cramps are often initiated by a change in speed, gradient or running surface. A classic example is cresting a hill and then accelerating downhill or running on to grass after hours on the tar.
Some people are simply more cramp-prone than others.
The most widely held belief is that cramp is due to dehydration and the loss of minerals such as sodium, potassium and magnesium. However, if this were so, then presumably all muscles would be affected and not just the large leg muscles, as is generally the case. A recent study on Two Oceans marathon finishers showed that the fluid and electrolyte balance of those who cramped and those who did not, was entirely normal. However what was abnormal in the crampers was the level of electrical activity in the muscle both during and after a muscle cramp. Whether electrolyte imbalances contribute to this loss of receptor function in working muscle is not yet known.