The investigators aim to investigate whether exercise therapy during 12 weeks including a lesson on general healthy lifestyle in adult patients with a moderately active disease is more effective, compared to control patients only receiving a lesson on general healthy lifestyle recommendations. The three main categories of outcomes are 1) health-related quality of life, 2) general health status of the patients 3) explorative outcomes. The primary outcome is health-related quality of life, the secondary outcome is general health status measured by waist circumference, disease activity scores, blood pressure, and blood lipids, and the third outcome are explorative outcomes (none-disease specific quality of life scores, biomarkers of C-reactive protein, fecal calprotectin and immunology markers including interleukins).

The investigators will apply a superior trial design in this randomized clinical trial with two arms, intervention and comparison. In both the intervention and comparison arm, the patients will receive the proper and usual medical treatment decided by their responsible physician and changes in the medical treatment is allowed at all times.

Inclusion Criteria:

• Patients with moderately active Crohn's disease or ulcerative colitis are defined by fulfilling all the following five criteria:

  1. Well-characterized Crohn's disease or ulcerative colitis (physician assessment) i. Fulfilling standard clinical, endoscopic, radiologic, and histological criteria

  2. A minimum of one-year disease duration from the time of diagnosis of Crohn's disease or ulcerative colitis to inclusion into the trial

  3. Any of the following pharmacological treatments in a period of three months prior to inclusion:

     i. Usage of 5-Aminosalicylic acid (5-ASA) ii. Usage of corticosteroids iii. Immunomodulators usage: Azathioprine (AZA), 6-mercaptopurine (6-MP), Methotrexate (MTX) iv. Biologics usage: Anti-TNFα (Infliximab, Adalimumab, Golimumab), Ustekinumab or Anti-integrin (Vedolizumab)

  4. Disease activity defined by clinical disease score:

     i. Harvey Bradshaw Index (HBI) 27 > 5 ii. Simple Clinical Colitis Activity Index (SCCAI) 29 > 5

  5. Marker for gastrointestinal inflammation:

     i. Fecal calprotectin (FC) > 200 mg/g

     Exclusion Criteria:

• 1. A language barrier that prohibits the exercise instructors/supervisors to give sufficient or safe instructions during the intervention or at the general health lesson.

  2. Known heart condition that prevents them to actively participate safely in the exercise intervention.

  3. Known pregnancy or planned pregnancy. 4. Disabling musculoskeletal injuries that prevent them to actively participate in the exercise intervention.

  5. Severe disease activity manifested clinically and with the need for urgent change in treatment evaluated by the responsible physician.