Muscular cramping may occur after one to two hours of exercise. Cramping may be induced in as little as 10 minutes after high intensity exercise targeting a specific muscle group.
The most commonly proposed causes exercise associated muscle cramps (EAMC):
Decreases in body mass, blood and plasma volume
Abnormal serum electrolyte concentrations
Decrease concentrations of sodium, potassium, magnesium, chloride, and/or calcium
As a result of sweating or over consumption of water during exercise
Exercising in heat which may result in electrolyte imbalances and dehydration
Dehydration and electrolyte loss are not the sole causes of EAMC because many individuals can experience cramping when they are hydrated and supplemented with electrolytes.
A more recent theory suggests that EAMC is related to sustained neural activity that results in fatigue. This idea is supported by athletes who are more likely to experience cramps toward the end of an event. A distinction has been made between EAMC that result from fatigue and that resulting from heat (in which electrolyte and fluid losses result in a contraction of extra cellular fluid space).
In one study, participants who experienced cramps had a higher average sweat rate than those that did not experience cramps. Subjects who experienced EAMC who consumed a carbohydrate - electrolyte beverage were able to exercise 150% longer before the onset of cramps.