If the legs feel weak, the causes are as follows: First, lack of calcium: especially children during the growth and development period and middle-aged and old people, it is easy to lead to weak legs after the lack of calcium. Muscle and fascia strain and cold: when the muscles and fascia of the legs are strained and cold, the patient will also experience leg weakness. Meniscus injury: patients with meniscus injury of the knee joint will have symptoms of weak legs when walking, as well as feeling weak and achy legs. Herniated lumbar disc: after compressing the spinal cord or nerve roots in the spinal canal, the patient will easily experience the symptom of weak legs. After the patient’s legs feel weak, we must consult the doctor to see what the cause is, and treat the cause of the disease to promote the reduction of the symptoms of weak legs, recovery, in order to restore the normal force of the leg activities.