Cramps are essentially tonic muscle spasms, and there are several common causes: 1, vascular in origin, common diseases include varicose veins of the lower extremities, venous thrombosis of the lower extremities, arteriosclerosis of the lower extremities, and even thrombo-occlusive vasculitis of the lower extremities, which can cause tonic muscle spasms of the calf muscles due to reduced blood supply. 2, neurological, common are nerve compression or chronic strain of the calf, lower extremity caused by lumbar diseases 3, electrolyte factors, hypocalcemia caused by a decrease in the concentration of calcium ions in the blood, can lead to cramp attacks.