Midnight foot tendon is mainly due to the muscle groups of the calf, under the action of various factors dysfunction, which leads to involuntary violent spasm and contraction of muscle fibers, there will be foot tendon symptoms. The common causes include the following: 1, patients in the daytime too much exercise or labor pressure too heavy, resulting in strain or injury to the calf muscles, the accumulation of local metabolites, in the middle of the night easily appear muscle group dysfunction, resulting in the symptoms of tendon. 2, seen in the sleep, the calf local lack of warm cover, especially in the summer air conditioning direct blowing, fan direct blowing or climate change 3, the calf has nerve disease, including neuritis, nerve injury, contusion, and lumbar disc protrusion, compression of the sciatic nerve root in the lower extremity, resulting in nerve abnormalities, resulting in the corresponding muscle dysfunction in the innervated area, which can also lead to the appearance of symptoms of tendon. 4. Patients with calcium deficiency, low potassium, etc., can also lead to muscle dysfunction, resulting in the appearance of hamstring symptoms. It is recommended that patients go to the hospital to improve the examination and make a clear diagnosis.