The most common cause of stiffness and pain in the calf muscles in the middle of the night is muscle cramps in the calf. There are many reasons for calf muscle cramps: first, there is a possibility of local cold, which leads to local muscle spasms, usually at night when sleeping without a blanket, which causes the calf muscles to catch cold and cause. Second, it may be caused by a lack of calcium. Third, it may be caused by local muscle strain, especially during the day, after long-term standing and walking or running and jumping and other strenuous exercise, some people have cramps at night because of fatigue. In addition, some lumbar disc herniation or lumbar spinal stenosis compress the nerve roots of the lower limbs, which may also lead to abnormal discharge of the nerves in the calf muscles at night, resulting in symptoms such as twitching of the muscles on the back side of the calf.