A novel feature of this study is the examination of different intensities of physical fitness-improving exercise in patients with anxiety disorders. This has not previously been performed and would yield valuable insight into dose-response associations between physical fitness and effects on the brain. Objective measurements of physical fitness and cognition are a great strength of the proposed study. Analyzing specific hormones and cytokines before and after the intervention, in relation to symptoms and functional data, may provide additional information about mechanistic aspects, treatment effect and prognosis. The proposed research also offers opportunities to develop effective treatment protocols to reduce the costs of sick-leave, an area of increasing interest world-wide.