The nerve that innervates the muscles in the front of the calf is the common peroneal nerve, which originates from the sciatic nerve. If the back of the foot cannot be turned up, it is often caused by damage to the sciatic nerve. The damage to the sciatic or common peroneal nerve is commonly caused by the following reasons: first, lumbar disc herniation or lumbar spinal stenosis, tumors in the lumbar spinal canal, compression of the nerve or damage to the nerve and the foot can not be upturned. Second, is there a tumor around the sciatic nerve in the thigh or hip or calf, which compresses the nerve and causes nerve damage, resulting in the inability to move the muscles in front of the calf, so that the foot cannot be uplifted. Thirdly, the nerve is not damaged due to inflammation or lesion of the nerve itself, and the corresponding innervated muscles are not able to move and the back of the foot is not able to turn up. Therefore, it is necessary to go to the hospital to find out the cause of the inability to turn up the back of the foot.