Quadriceps retraining, especially the vastus medialis oblique muscle strengthening, plays an important role in clinical management of patellofemoral pain syndrome. Vastus medialis oblique muscle roles as a dynamic stabilizer during the functional knee movement. It can generate a medial pulling force to patella against the lateral pulled by vastus lateralis. Thus it improves the patellofemoral joint compression force, reduces the knee pain, increases functional abilities, and patients’ quality of life.