The most common cause of calf muscle stiffness with pain in the middle of the night is caused by calf muscle cramps. There are many reasons for calf muscle cramps: first, there may be a local cold, which leads to local muscle spasms, usually sleep at night without a quilt, which leads to the calf muscle cold and caused. Second, it may be caused by calcium deficiency. Third, it may be local muscle strain, especially during the day, after standing and walking for a long time or running and jumping and other strenuous exercise, some people at night because of fatigue and cramps. In addition, some lumbar intervertebral disc herniation or lumbar spinal stenosis compresses the nerve roots of the lower limbs, which may also lead to abnormal discharges of the nerves of the calf muscles at night, resulting in twitching of the muscles of the back of the calf and other symptoms.