Randomization
We used cluster randomization on health care center level to prevent contamination effects. Of the 15 health care centers, eight were randomized to the PARASOL intervention and seven the control group. Concealment of allocation was ensured since a person outside of the research team performed the randomization. The health care centers were informed about their allocation by email. The health care professionals and patients were not blinded. The main investigators were also not blinded to group assignment.Physical therapists and mental health nurses of the health care centers assigned to the intervention group were asked if they had a special interest or already experience in treating patients with MUPS. The physical therapists and mental health nurses signed up were instructed how to treat patients with moderate MUPS during a two-day training on the content of the PARASOL intervention. Furthermore, a booster session after six months was conducted to ensure adherence to the treatment protocol. The physical therapists and mental health nurses of the control health care centers were not trained.