The inability to stand up with weak thighs may be caused by the following reasons: First, it may be caused by excessive fatigue. If the patient does excessive exercise activities for the lower limbs, then it may cause muscle fatigue in the thigh area, which in turn leads to weakness of the lower limbs. Second, this condition may be caused by lesions related to the nervous system. There are many types of such lesions. For example, when there is an injury to the spinal cord, it may cause weakness in the lower extremities. In the case of central nervous system lesions, such as cerebral infarction and cerebral hemorrhage, it may also cause weakness of the thighs. In addition, if there is some peripheral nerve entrapment, such as in the femoral nerve, it may also lead to similar symptoms. Third, this condition may be caused by muscle atrophy. Such symptoms are often seen in patients after prolonged bed rest and braking, resulting in disuse atrophy of the muscles of the lower limbs. In this case, during the patient’s weight-bearing activities on the ground, there may be weakness of the thigh muscles and lead to the above symptoms. Fourth, this condition may also be caused by some autoimmune related diseases. For example, when the patient has a series of pathologies such as Greenbrier syndrome and myasthenia gravis, there may also be similar symptoms.