Sitting for a long time in the middle of the buttocks to consider and sacrococcygeal ligament strain, lumbar disc herniation, ankylosing spondylitis and so on. 1. Sacrococcygeal ligament strain: Sacrococcygeal ligament strain due to frequent sedentary or frequent bending of the waist, appearing in the middle of the buttocks pain, rest can be alleviated. 2. Lumbar disc herniation: after sitting for a long time, the load borne by the lumbar region increases, and it is easy for nerve compression to aggravate, resulting in pain in the middle of the buttocks, and in some cases, there will be pain and numbness in the lower limbs. 3. Ankylosing spondylitis: when sitting and standing up for a long time may appear lumbosacral pain, appropriate activities can be reduced, accompanied by morning stiffness, serious spinal deformation may occur. Sitting for a long time in the middle of the buttocks pain causes more, if the rest pain did not improve, it is recommended to seek medical attention.