Muscle cramps occur most often at night when you are sleeping, but they also can occur when you exercise vigorously, tear a muscle, or keep one leg in an awkward position, such as sitting in a chair in the same position for a long time. Muscle cramps are classified into those that occur during exercise and those that can occur at any time not related to exercise, usually at night. Cramps That Occur During Exercise Lack of electrolytes is a more common cause of muscle cramps during exercise than lack of water (BMJ Open Sport Exerc Med, Mar 5, 2019;5(1):e000478). Electrolytes are minerals that are essential for body functions, including sodium, potassium, calcium, bicarbonate, magnesium, chloride, and phosphate. Having low blood levels of sodium (salt) is a well-known cause of muscle cramps. Dehydration, by itself, is a far less common cause of cramps. You can be salt deficient and still …