Cramps, also known as muscle spasms, calf muscle spasms may be caused by overwork, poor sleeping position, cold stimulation, calcium deficiency and other factors. 1. Excessive fatigue: Exercise too long, will make the lower limbs overworked, resulting in the accumulation of local acidic metabolites, thus causing calf muscle spasm. 2. Poor sleeping posture: lying on the back for a long time, with the quilt pressed on the feet; or lying prone for a long time, with the feet against the bed, can make certain muscles of the calf for a long time in a state of absolute relaxation, which is easy to cause passive contracture of the muscles, and calf muscle spasms. 3. Cold stimulation: the calf muscles in the cold stimulation, can also appear muscle spasm. 4. Calcium deficiency: low calcium concentration in the blood can increase the excitability of the muscle, which is easy to have muscle spasm. In addition, there are many other causes can cause calf muscle spasm, such as high fever, epilepsy, etc., if accompanied by other symptoms, you should consult a doctor in time.