Using a prospective cohort design the investigators will investigate the effect of a novel treatment strategy aimed at temporary reduction in the loading of the patellofemoral joint by activity modification. After inclusion, the custody holder and the adolescent with PFP will be informed to begin a 4 week activity modification period and avoid all sports activity including school sports. This protocol will cause a temporary reduction in the loading of the patellofemoral joint. At 4 weeks they are instructed to begin a predefined training protocol involving graded exercises. The purpose of the graded exercises is to increase loading capacity of the tissue around the knee.