Adolescents will be recruited from a population-based cohort from Aalborg and Copenhagen consisting of a total of 16 public schools. This cohort will allow for recruitment of adolescents with PFP from the following categories 1) adolescents not participating in sport outside school; 2) adolescents involved in sports a minimum of 3 times per week. In addition, a randomly recruited age- and gender-matched pain-free group from the same cohort will be recruited to form a control group.