Study population
A total of 19 patients with IBD were included in the study. Inclusion criteria for all IBD patients were age ≥18 years and diagnosis of Crohn’s disease or ulcerative colitis made by a gastroenterologist. IBD patients were not included when they used specific biologicals (infliximab, adalimumab, golimumab, ustekinumab) as these might change the immune response. All patients completed a distance of 30, 40 or 50 km per day on three consecutive days at a self-selected pace. As a control group, a total of 19 age- and gender-matched healthy controls were recruited who also underwent the same repeated exercise bouts. This study was approved by the Medical Ethical Committee region Arnhem-Nijmegen (CMO registration number: 2019-5375) and was registered at trialregister.nl as NL7872. All participants provided written informed consent prior to participation. This study was conducted in accordance with the Declaration of Helsinki.