The causes of weakness in one leg are as follows: 1. lumbar disc herniation, due to lumbar disc herniation, the nerve roots that govern the sensation and movement of the lower limbs are compressed by the herniated disc, and symptoms of numbness and weakness in the corresponding radiation area of the unilateral lower limb appear. 2. pear-shaped muscle entrapment syndrome, the sciatic nerve is compressed when the pear-shaped muscle passes, and edema and degeneration occur, manifesting as numbness and weakness in the affected lower limb. 3. sports injuries, the Lower extremity muscle strain, seen after strenuous exercise and heavy laborers, local injury to the lower extremity muscles accompanied by aseptic inflammation in the soft tissues, manifested as lower extremity edema, pain and lower extremity weakness. 4, hip and knee joint lesions, including hip and knee osteoarthritis, rheumatoid arthritis, gouty arthritis, etc., manifested as joint pain, decreased muscle strength of the surrounding soft tissues, lower extremity soreness and weakness.