Impact of hypoxic exercise on cardiac stress markers, angiogenic pathways, and antioxidant defence in junior endurance athletes

Abstract Background Regular physical activity is a key stimulus for adaptive changes in the cardiovascular system. However, the combined effects of hypoxia and endurance exercise on cardiac hemodynamics and angiogenic responses in youth athletes remain insufficiently explored. Intermittent hypoxia - defined as alternating short exposures to hypoxia and normoxia may stimulate beneficial adaptations, including modulation of hypoxia-inducible factor 1α (HIF-1α), enhancement of angiogenesis-related pathways, and protection against ischemia–reperfusion injury. Purpose This study investigated the effects of high-intensity interval training performed in a hypoxic environment on cardiac biomarkers, omega-3 index, and antioxidant status in junior athletes. Methods Twelve athletes (age 15.7 ± 1.0 years) completed interval training sessions under normobaric hypoxia (FiO2 = 15.2%; LOWOXYGEN Technology GmbH, Berlin, Germany) and normoxia. Blood samples were collected before and after each session. Cardiac biomarkers -including cardiac troponin T (cTnT), creatine kinase myocardial band (CK-MB), and heart fatty acid-binding protein (H-FABP) - as well as HIF-1α, vascular endothelial growth factor (VEGF), antioxidant status, and membrane fatty acid composition (ω-3 index; Sannio Tech, Italy) were assessed. Differences between conditions (Hyp vs. Nor), time points (pre- vs. post-exercise), and exercise intensity (rest vs. maximal effort) were evaluated using repeated-measures ANOVA with Bonferroni post-hoc testing (p 0.05). Results A significant effect of exercise and hypoxic exposure was found for CK-MB activity (F = 5.9; p 0.05) and cTnT levels (F = 7.2; p 0.03). CK-MB activity was significantly lower after hypoxic training compared to normoxia (14.7 ± 2.2 vs 11.7 ± 2.1 U/L; p 0.001). Hypoxic training also resulted in a significant increase in VEGF concentrations compared to normoxia (51.4 ± 11.6 vs. 74.5 ± 12.3 ng/mL; p 0.001). The ω-3 index increased significantly after hypoxic training, accompanied by a reduced AA/EPA ratio (p 0.05). Antioxidant markers showed minimal sensitivity to oxygen conditions; however, exercise had a significant effect on GPx levels (p 0.001), and superoxide dismutase demonstrated an increasing trend under hypoxia. Conclusion Normobaric hypoxic exercise training induced beneficial changes in selected cardiac biomarkers, angiogenic signaling, and fatty acid profiles in youth athletes. These findings suggest that hypoxic training may support cardiovascular adaptation and potentially reduce long-term cardiovascular risk in young athletes.