If there is one thing every runner dreads for its devastating potential to reduces 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.

• Cramp is more common in males than in females.
• Cramp is associated both with the duration and intensity of exercise - the further and the faster the more likely cramp is to occur.
• Onset of cramp is usually after 30km in a distance race, regardless of running speed.
• Cramp during exercise is almost always in the large muscles that span two joints - the hamstrings, quadriceps and calf (gastrocnemius) muscles.
• 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. These minerals play a critical role in muscle contraction, so any imbalance would affect muscle function. However, if a runner were to become sufficiently electrolyte depleted while running, it is unlikely that only one or two muscles would cramp – surely the electrolyte loss would affect all muscles equally ? As it is, the muscles most likely to cramp are the comparatively large calf, hamstring and thigh muscles.

Researchers at the University of Cape Town did a study on runners who regularly suffered cramp during distance races. Blood samples were taken before and after the Two Oceans marathon, and the glucose, sodium, potassium, calcium and magnesium levels measured. And guess what? Of the 44 runners in the study, 21 suffered cramp during the event, and 23 did not. However, the sodium, potassium and magnesium levels of all those who cramped was entirely normal, as was that of the non-crampers. All subjects were well hydrated at the finish. The conclusion then: mineral imbalance and dehydration are not the cause of cramp.

So what is the cause?
In the same study, the runners who developed cramp severe enough to prevent them walking were monitored in the medical tent after the marathon. The electrical activity in the affected muscle was measured on admission to the tent and again 60 minutes later when the cramp had stopped. These recordings showed that even while not in a cramped state, the muscles of affected runners showed very elevated levels of electrical activity.

This suggests that some runners are more vulnerable to cramp due to hyper-excitable muscle, which is more likely to malfunction during periods of prolonged use. It is thought that receptors in the muscle tissue, which exist to co-ordinate muscle contraction and relaxation by informing the brain about the degree of stretch or tension in a muscle, cease to work adequately. The result is that the brain gets the incorrect information and the muscle remains in a contracted state. What causes these receptors to stop working is not known, but the obvious reason is that they also fatigue with prolonged and repetitive stress.

Magnesium deficiency is most commonly blamed for causing cramp. Magnesium plays a role both in muscle function and energy production but during prolonged exercise it appears that magnesium gets relocated in the body as opposed to lost via sweat or urine (reason not known). Hence magnesium imbalance relative to other electrolytes during exercise could be one of the factors involved in cramping in fatigued muscle. However, ingesting magnesium supplements daily is unlikely to reduce the risk of cramping because the problem is not a lack of magnesium per se – and the body will just excrete any excess magnesium. Whether taking magnesium during prolonged exercise reduces cramp risk or severity has never been scientifically studied.

Another misconception is that lactic acid (melksuur) build-up causes cramp. This is incorrect, for several reasons. High levels of lactic acid in the muscle contribute to fatigue by inhibiting muscle contraction. On the contrary cramp is a sustained muscle contraction. Lactic acid is generated during high intensity, but in endurance events lactic acid production is minimal. Also, lactic acid does not stay in muscle for very long – it is shunted off to the liver to be recycled into more glucose. It does not form crystals, either in the muscle or anywhere else, so this additional explanation for cramp and also muscle pain is also without physiological foundation.

What can you do then to prevent muscle receptor fatigue and consequent cramp?

Train:
You have to teach muscle what you want it to do at a certain pace, over varying gradients for long periods of time. Ensure that you train on terrain similar to that you plan to race on.

Get strong:
The stronger the muscle, the more fatigue resistant and therefore possibly less cramp prone. Do hill work and if you have the opportunity, specific leg strengthening workouts in the gym.

Stretch regularly:
Increased muscle flexibility might help to counteract cramp. When cramp strikes, stretch it out. You have to unlock the muscle from its contractile circuit.

Be very cautious when changing speed or gradient in the latter stages of a race. Fatigued muscle cannot readily adapt to the changing demands made upon it.

Health & Nutrition Advice & Information supplied by Lindsay Weight