The possible reasons for thigh muscle weakness can’t stand up are exertion, hypokalemia, lumbar intervertebral disc herniation, muscle atrophy and so on. 1. Exhaustion: After a long time of physical labor, thigh muscle strain and lactic acid accumulation can cause thigh pain and weakness, which is a normal phenomenon, and proper rest is sufficient. 2. Hypokalemia: Because of the large loss of potassium after diarrhea or previous endocrine diseases such as hyperthyroidism, hypokalemia is caused by weakness of the lower limbs, palpitation, irritability, loss of appetite and other symptoms. 3. Lumbar intervertebral disc herniation: Lumbar intervertebral disc herniation compresses the femoral nerve, which can cause thigh pain and fatigue, mostly accompanied by pain and discomfort in the lumbar region. 4. Muscle atrophy: If there is a lack of activity after a fracture, it may cause muscle atrophy of the lower limbs and a decrease in muscle strength, thus causing weakness of the lower limbs. Causes of thigh muscle weakness can not stand up more reasons, may also be related to lumbar spinal stenosis, hip osteoarthritis, Green-Barre syndrome, etc. If the symptoms continue to be unrelieved, it is recommended to consult a doctor in a timely manner, to clarify the cause of the disease, and to carry out targeted treatment.