Climbing stairs legs soft and acidic weakness has more reasons, may be related to lack of exercise, fatigue and other physiological factors, but also may be related to anemia, knee disease, lumbar spine lesions and other pathological factors. 1. Physiological factors: if the lack of exercise can lead to poor muscle strength, or excessive exercise leading to muscle fatigue and other factors, there will be climbing stairs leg soreness and weakness, it is recommended that such people should be moderate exercise. 2. Anemia: the number of red blood cells in the body will be reduced, resulting in a relative reduction in the number of oxygen-carrying cells, so that the whole body appears to be hypoxic symptoms, and the muscles are in a state of hypoxia, there will be soreness and weakness of the symptoms. 3. Knee diseases: degenerative knee joints, meniscus injuries, ligament injuries, etc. can lead to articular cartilage wear and tear or knee joint instability, as well as joint mobility disorders, therefore, in the process of climbing stairs will cause weakness and aching in the legs. 4. Lumbar spine lesions: lumbar disc herniation, spinal stenosis and other lumbar spine lesions, due to the compression of the nerve root, can lead to pain and numbness in the lower limbs, and will also appear in the calves of the soreness and weakness and other symptoms. Climbing stairs leg weakness can also be seen in other causes, it is recommended to consult a doctor in a timely manner, follow the doctor’s instructions for relevant examinations, with the help of the doctor to clarify the cause, and targeted treatment or therapy.