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Cramps are spasmodic, painful, involuntary muscle contractions. This page is focused on Exercise Associated Muscle Cramps (EAMC), though there are other types. Many runners suffer from cramps, and sometimes cramps can be severe enough to prevent the completion of an event, or catastrophically impact performance. There are two leading contenders <ref name="twooptions"/> for the cause of muscle cramping; sodium deficiency [[Sodium Deficiency]] and muscle fatigue.

The initial stages of sodium deficiency [[Sodium Deficiency]] produce dehydration as the body excretes water to keep the blood sodium concentration at the right level. More extreme sodium deficiency[[Sodium Deficiency]], or excessive hydration, can lead to [[Hyponatremia]] where the sodium concentration in the blood drops. Either of these conditions are believed to interfere with nerve function and cause cramping. A study<ref name="Jung"/> in 2005 showed that a carbohydrate/electrolyte drink delayed cramps in athletes that have a history of cramping. There is also a large body of anecdotal evidence that increased salt reduces cramping.

[[Sodium deficiency Deficiency]] is easy to treat and pretty much risk-free. [[Sodium deficiency Deficiency]] can be either chronic (long-term) or acute (short-term). Increasing the salt in your diet can help prevent chronic sodium deficiency[[Sodium Deficiency]], and any excess will be naturally excreted. You may need to add far more salt to your diet than you expect. To prevent acute sodium deficiency [[Sodium Deficiency]] you should add extra salt to the drink you take while running. I generally add a 1/4 teaspoon of salt to each quart of drink. To treat sodium deficiency [[Sodium Deficiency]] triggered cramping, one recommendation is 3 g (1/2 teaspoon) of salt added to 0.5 L (~16oz) of water or sports drink<ref name="twooptions"/>, which is rather salty and unpleasant shouldn't trigger nausea. [[Heat Acclimation Training]] may also help prevent cramping.

One theory behind muscle fatigue causing cramping is the idea that a cramping muscle has lost its inverse stretch reflex. The inverse stretch reflex is stimulated by a prolonged stretch and causes the muscle to relax. If a muscle's inverse stretch reflex becomes weakened, it will tend to contract strongly. The theory also explains why cramps are more likely to occur in muscles that are contracting in a shortened position (calf, hamstring). This theory suggests that stretching [[Stretching]] will help with cramping, not because of increased flexibility, but because it will reinforce the inverse stretch reflex.

File:RunningForm-L.jpg|As the right leg decelerates for pawback, the momentum of the foot will cause it to come up towards the shin, stretching [[Stretching]] the calf slightly.

Changing running form [[Running Form]] can be difficult and risky, and evaluation should be performed using something like high-speed video to verify that a problem exists. One alternative is to vary your pace and running style slightly every few miles. This could be to pick up the pace slightly for 20 to 30 seconds, or to consciously raise the knees higher, or any other variation that helps to stretch your muscles a little.

The following criteria can be used to determine if the cramping is due to muscle fatigue or sodium deficiency[[Sodium Deficiency]]:* '''Sudden onset'''. [[Sodium deficiency Deficiency]] tends to cause minor cramping that escalates whereas muscle fatigue is often sudden and dramatic.* '''Localized'''. Muscle fatigue is usually localized to specific muscles such as the calf where I sodium deficiency [[Sodium Deficiency]] is more generalized.* '''Response to treatment'''. If the cramping is relieved by stretching [[Stretching]] it is most likely to be from muscle fatigue, but if the cramping is relieved by hydration and electrolytes then it is likely to be sodium deficiency[[Sodium Deficiency]]. Cramping that is relieved by pickle juice or vinegar could be because of either underlying cause is this treatment is working on the underlying behavior of the nerves.