Strenuous exercise induces different stress-related physiological changes, potentially including changes in intestinal barrier function. In the Protégé Study (ISRCTN14236739; www.isrctn.com) we determined the test-retest repeatability in responses to exercise in well-trained individuals.<br/>Eleven well-trained males (27±4 years old) completed an exercise protocol that consisted of intensive cycling intervals, followed by an overnight fast and an additional 90 min cycling phase at 50% Wmax the next morning. The day before (rest), and immediately after the exercise protocol (exercise) a lactulose/rhamnose solution was ingested. Markers of energy metabolism, lactulose/rhamnose ratio, several cytokines and potential stress-related markers were measured at rest and during exercise. In addition, untargeted urine metabolite profiles were obtained. The complete procedure (Test) was repeated one week later (Retest) to assess repeatability.<br/>Metabolic effect parameters with regard to energy metabolism and urine metabolomics were similar for both the Test and Retest period, underlining comparable exercise load. Following exercise, intestinal permeability (one hour plasma lactulose/rhamnose ratio), serum interleukin-6, interleukin-10, fibroblast growth factor-21, and muscle creatine kinase levels were only significantly increased compared to rest during the first test and not when the test was repeated.<br/>Responses to strenuous exercise in well-trained young men, as indicated by intestinal markers and myokines, show adaptation in Test-Retest outcome. This might be due to a carry-over effect of the defense mechanisms triggered during the Test. This finding has implications for the design of studies aimed at evaluating physiological responses to exercise.