Pain and weakness in the lower extremities are commonly caused by the following: 1. lumbar spine diseases, due to lumbar spine diseases causing compression of sciatic nerve roots in the lower extremities, resulting in radioactive pain and weakness in the lower extremities. 2. metabolic diseases seen in the whole body, such as abnormal calcium and phosphorus ion metabolism and potassium ion deficiency, can produce pain and weakness in the lower extremities. 3. poor blood circulation in the lower extremities, such as Vasculitis or localized compression of blood vessels can produce pain and weakness in the lower limbs. This problem should go to the hospital for detailed examination, you can go to the orthopedic department for examination, find the cause and take the appropriate treatment.