What causes cramps in the body?

There are two basic causes of cramping. One is inadequate oxygenation of muscle, and the other is lack of water or salt. Cramps from poor oxygenation can be improved by rapid deep breathing, as well as stretching the muscle. Cramps from lack of salt and water can be treated by stretching the muscle, and of course drinking water and increasing salt intake. Pounding on the muscle can increase soreness. Muscle cramps in particular can be treated by applying a soft massage on the cramped muscle, stretching the muscle and applying heat or cold. Heat improves superficial blood circulation and makes muscles more flexible, so some people find that heat is more soothing for muscle cramps than applying ice. Electrolyte disturbance may cause cramping and tetany of muscles, particularly hypokalemia (a low level of potassium) and hypocalcemia (a low level of calcium). This problem can be solved by drinking electrolyte enhanced fluids, such as Gatorade, after strenuous muscle activity. Muscle cramps may be a symptom of Hypothyroidism.

I was told that cramps can be caused by a lack of salt