(Ultra-)inflammation or adaptation? Comparison of different ultramarathon distances and their effect on the immune system

Background: Ultra-endurance sports like running over several hours or days exhibit great physical, psychological and metabolic strain on the respective athlete. Although the impact of ultramarathon running on the inflammatory/immunological system gained interest in the last years, there is no study that examined the effect of different running distances on inflammatory/immune system responses. Methods: During a non-stop ultramarathon, blood and saliva samples were collected before (Pre) and after the race (Post), and analyzed for changes in blood cell variables (immune cells leukocytes/thrombocytes), cytokine response (pro- and anti-inflammation: IL-6/IL-10/IL-1ra/IL1-beta/TNF-alpha), and stress-related parameters (CRP as acute phase protein; uric acid for oxidative stress; cortisol/kynurenine for general stress and energy metabolism). Biomarkers were supplemented by a stress-related questionnaire and 1) analyzed for the whole group of finishers (N = 43; 16f/27m) and 2) compared between the respective running distances (100/160.9/230 km). Results: Leukocyte and thrombocyte count increased Post in all runners, with a more pronounced leukocyte response observed in 100 km vs. 160.9 km. IL-6/IL-10/IL-1ra increased Post in all sub-groups, whereas IL1-beta decreased only in the whole group. Stress/immune response showed an increase of salivary cortisol and CRP in all runners. Sub-group analysis revealed highest cortisol and CRP concentrations in 230 km Post race. Conclusions: Ultramarathons differ in the physiological strain they impose, with running distance being an important factor. Especially 100 km (faster pace, shorter duration) and 230 km (slower pace, longer duration) runners exhibited distinct inflammatory/immunological responses. Thus, broad generalizations regarding the impact of a given ultramarathon on the immune system and potential post-race infection risk are unwarranted, and individualized guidance is currently more effective.