A cramp is an intense, involuntary contraction of a muscle that usually occurs during or immediately after exercise. Cramps were traditionally thought to stem from fluid or electrolyte imbalances, but they are not always the reason. Cramps may occur following chronic muscle use by individuals, such as musicians, who are not sweating.
Cramps have also been attributed to extreme environmental conditions or metabolic abnormalities, but again there are examples where this doesn’t hold. Cramps typically occur in situations that cause muscle fatigue, such as toward the end of long, strenuous or intense rides.
A current theory suggests muscle cramps result from fatigue that triggers abnormal neural activity. There’s an increase in neural input telling the muscle to contract, and a decrease in signals telling the muscle to relax. The result is a vigorous contraction of part or all of the muscle.
The presence of dehydration is thought to accentuate muscle fatigue, adding insult to injury. Cramps are most common in muscles that span two joints. The hamstrings are a great example. Other two-joint muscles include part of the quadriceps (thigh muscle) and the gastrocnemius (calf muscle).