Exercise stress to assess health resilience

Health can be defined as the capacity of the body to maintain homeostasis and adapt to physiological stressors through coordinated protective and recovery mechanisms. This thesis investigates whether dynamic biomarker responses to controlled physical stress can be used to quantify intestinal and immune resilience. Using standardized bicycle ergometer protocols, healthy young men were subjected to exercise at varying intensities and hydration states, while a broad panel of metabolic, immune, hematological, and intestinal biomarkers was monitored over a 24-hour kinetic window. The results demonstrate that numerous biomarkers exhibit time-dependent responses to exercise, with the magnitude of these responses strongly influenced by exercise intensity and hydration status. Moderate exercise (50% Wmax) was sufficient to induce measurable physiological and immunological changes, whereas high-intensity exercise (70% Wmax) and intermittent protocols elicited more pronounced responses. Dehydration amplified biomarker changes and negatively affected intestinal physiology. Intestinal biomarkers such as plasma citrulline and serum intestinal fatty acid-binding protein (iFABP) reflected exercise-induced alterations in intestinal metabolic activity and epithelial integrity, respectively. In parallel, leukocyte subsets displayed intensity-dependent, biphasic kinetic responses indicative of transient immune activation and recovery. Exploratory analysis of salivary biomarkers identified secretory leukocyte protease inhibitor (SLPI) and matrix metalloproteinase-9 (MMP-9) as potential non-invasive indicators of physiological stress. Interlaboratory comparison across multiple research centers confirmed that the standardized exercise model produces reproducible biomarker kinetics, demonstrating its robustness and transferability. Together, these findings show that dynamic biomarker responses to exercise provide valuable insight into intestinal and immune resilience. The standardized bicycle ergometer test therefore represents a promising tool for assessing health status and evaluating the effects of lifestyle, nutritional, or environmental interventions on systemic health resilience.