The pain on the outside of the knee after running needs to be considered that it may be caused by trauma, osteoarthritis, vitamin D deficiency and other factors. 1. Trauma: frequent running if excessive exercise or improper activities, can lead to muscle strain around the knee joint, and even lateral collateral ligament, meniscus injury and other parts of the injury, the appearance of running knee pain, need to pay attention to rest, reduce the amount of exercise, protect the knee joint. 2 osteoarthritis: knee degenerative lesions or old trauma protection is not appropriate, can develop into osteoarthritis, can be manifested as running knee pain, need to appropriately reduce the amount of activity and intensity of exercise, avoid climbing stairs, climbing and long time running and other sports. 3. Vitamin D deficiency: caused by the lack of vitamin D in the body, including insufficient intake of vitamin D, insufficient synthesis of vitamin D, decreased sensitivity of vitamin D in the body, etc., which can lead to osteoporosis, bone pain, muscle atrophy, bone fracture and other symptoms, so some of the patients will have the symptom of pain on the outside of the knee after running. Daily life should eat more food containing vitamin D such as deep-sea fish, animal offal and other foods, usually more sunshine. There are many other causes of lateral knee pain after running, and it is necessary to go to the hospital for examination to clarify the specific causes.