Antioxidant-Enzyme Profiles in Youth Athletes: Associations of SOD and GPX with Exercise and Implications for Endothelial Health

Oxidative stress is a key driver of endothelial dysfunction and early cardiovascular risk. Antioxidant enzymes such as superoxide dismutase (SOD) and glutathione peroxidase (GPX) are vital for vascular protection, especially during growth. While exercise-induced redox adaptations are well established in adults, data in pediatric athletes are limited. This cross-sectional study examined associations between training load and systemic antioxidant enzyme activity in 203 youth athletes aged 10-16 years, also considering sex, age, sports discipline, and redox phenotypes. Physical activity was assessed via validated questionnaires and expressed as weekly hours and MET-hours. Fasting blood samples were analyzed for SOD and GPX. Statistical tests included <i>t</i>-test, ANOVA, regression, and k-means clustering. Antioxidant enzyme levels were stable across training volumes, sports disciplines, and age groups. Boys showed significantly higher SOD than girls (259.43 ± 54.02 U/mL vs. 226.93 ± 48.22 U/mL, <i>p</i> < 0.001); GPX levels were similar between sexes. Cluster analysis identified three distinct redox profiles with differing training and sex distributions. No linear association was observed between training load and enzyme activity. Findings suggest that youth athletes exhibit robust antioxidant defenses, with individual and sex-related factors playing a more prominent role than training volume. These results highlight the value of regular physical activity for vascular health during development and the need for longitudinal studies to track redox adaptation.