Weakness and tenderness of the legs may be related to prolonged climbing, cycling and other high-intensity exercise, but also need to consider lumbar spine lesions, peripheral nerve disease, myasthenia gravis and other pathologic factors. 1. High-intensity exercise: prolonged mountain climbing, bicycling and other activities, resulting in excessive fatigue, lack of timely rest, lack of sleep, etc., can cause weakness and tenderness of the legs. 2. Peripheral nerve diseases: such as Guillain-Barré syndrome, mostly related to infection, autoimmunity and trauma. It damages most of the spinal nerve roots and peripheral nerves, and often involves the cerebral nerves. Paralysis and weakness of the lower limbs can occur, and the decrease of muscle strength can be seen on physical examination, accompanied by the weakness of the upper limbs. 3. Myasthenia gravis: The post-synaptic membrane of the nerve-muscle junction is lesioned, and the skeletal muscles are easily fatigued, and the symptoms are aggravated after activities. Weakness of the lower limbs can occur, characterized by morning and evening episodes. 4. Lumbar spine lesions: for example, lumbar disc herniation, due to lumbar disc degeneration and other causes of intervertebral disc fibrous ring rupture, nucleus pulposus tissue prolapse, compression of the nerve. When the nerve root is severely compressed, nerve paralysis, muscle paralysis, weakness of the lower limbs can occur. If the weakness of the legs does not improve after resting, it is recommended to consult a doctor for further examination to clarify the cause of the disease and to carry out targeted treatment with the help of the doctor.