Between November 2012 and September 2013, we included app. 500 municipal workers perfoming either manual work, administrative work or a combination of the two. Participants worked in 5 different municipal workplaces. These workplaces were characterized by being devided into 'natural working unit', which had no or very little daily contact. All 5 workplaces participated with at least 2 units. Thus 11 units contributed to the data. Baseline assessment took place during right upon recruitment prior to randomization.