This is from the link above.
They may be harmless but they are very painful. I have had these off and on pretty much since about age 25. I have jogged on and off since high school and they seem to occur more often, oddly enough, when I am not jogging regularly. The opposite would seem to make more sense to me. I just grit my teeth and massage my calf until they go away.Most of the time, true night leg cramps occur for no known reason, and they're harmless. However, in rare situations, night leg cramps can be associated with an underlying disorder — such as peripheral artery disease or diabetes.