There are many reasons why sitting up for a long time and legs won’t go, mainly related to lactic acid accumulation, nerve compression, knee arthritis and joint free body. 1. Lactic acid accumulation: may be due to long-term pressure on the waist and legs resulting in poor local blood circulation, lactic acid and other metabolites accumulate in the thighs, resulting in paralysis of the thigh muscles, the symptoms of weakness, appeared to sit for a long time up the legs will not go. 2. Nerve compression: the sciatic nerve in the lower limbs after sitting for a long time by the extrusion of the nerve will also appear transient ischemia, resulting in lower limb numbness symptoms, then walking will appear the phenomenon of the leg can not make strength. 3. Knee arthritis: osteoarthritis of the knee and rheumatoid arthritis and other diseases, but also because of the articular cartilage and the joint capsule and synovial tension and spasm, resulting in limited joint activity, appearing to sit for a long time to get up the legs will not go. 4. Joint free body: when there is a free body in the knee joint, it will lead to the situation that the leg will not walk after sitting for a long time because of the free body. If there is no recovery after a short period of time and the symptoms persist, it is necessary to consult a doctor in time to carry out relevant examinations to see whether there is a nerve strain and other conditions, and then carry out targeted treatment under the guidance of the doctor.