The purpose of the study is to investigate the treatment effects of hip adduction combine knee extension exercise in patients with patellofemoral pain syndrome. We use muscle morphology of quadriceps muscle, pain, and functional abilities as the main outcome measures. Besides, we will make further compare with traditional knee extension exercise. The first hypothesis of the study is that patients with patellofemoral pain syndrome will get improvement in muscle morphology of quadriceps muscle, pain, and functional abilities after hip adduction combine knee extension exercise training . The second hypothesis is that patients with patellofemoral pain syndrome who receive hip adduction combine knee extension exercise training will get more improvement in muscle morphology of quadriceps muscle, pain, and functional abilities than patients who receive traditional knee extension exercise training.