Weak legs and knees may be caused by soft tissue strain, lumbar disc herniation, physiological phenomena and other reasons. 1. Soft tissue strain: it may be the weak legs and weak knees after competitive sports or excessive labor due to the accumulation of local lactic acid, resulting in sore legs and fatigue. 2. Lumbar disc herniation: It may be caused by lumbar degeneration and injury. The protruding place can compress the lumbar nerve root, causing abnormalities in the nerves that innervate the muscles of the lower limbs, resulting in neurogenic intermittent claudication, or the phenomenon of weak legs and weak knees. 3. Physiological phenomenon: with age, joint cartilage degenerative disease, patients may be accompanied by weakness, activity disorders, osteoporosis, muscle atrophy and other symptoms, the phenomenon of weak legs and weak knees can occur. Weak legs and knees can also be seen in hypokalemia and other reasons, if you exclude physiological phenomena, it is recommended to go to the hospital in a timely manner, clear the cause of the disease and then follow the doctor’s instructions for treatment, to avoid delaying the condition.