This exploratory study's primary objective is the changes of irritable bowel syndrome (IBS) symptom severity by cardiovascular endurance training (CET) in relation to the baseline sedentary or non-active lifestyle. Secondary endpoints focus on the mechanisms associated with these changes. These mechanisms relate to dietary adaptations, changes in anxiety, depressive comorbidity, somatisation, alterations in the gut microbiome or metabolome, body composition and measures of cardiovascular fitness. Virtually all IBS guidelines mention lifestyle modifications as a management option. Research on the role of physical activity remains underassessed as compared to the other interventions. Therefore, an exploratory proof-of-concept study will investigate the influence of regular physical exercise on symptoms in a small group of IBS patients. This study will gather data on putative underlying mechanisms related to dietary factors, faecal microbiome and metabolome, mental well-being, body composition and cardiovascular fitness.