What is causing these charley horses?

Muscle cramps – also known as a Charlie horse, is a sudden, painful muscle contraction of a muscle that can be so intense that we can't use the muscle until the cramp eases. It can be caused by a lack of magnesium, or a potassium deficiency. But beware – it can also signal the onset of vascular disease, so if you find that you are cramping more than usual, please check this out. Kidney dialysis can also bring them on.