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 t-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, p < 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.

Adolescence is a critical window for cardiovascular (CV) development, yet the molecular drivers of vascular adaptation to regular exercise in youth remain poorly understood. This cross-sectional study assessed vascular structure and function alongside endothelial, metabolic, and lipoprotein biomarkers in 203 healthy young athletes (aged 10–16). Vascular phenotyping included carotid intima-media thickness (IMT), pulse wave velocity, and carotid deformation indices (strain, strain rate). Circulating nitric oxide (NO), endothelin-1, free triiodothyronine (fT3), leptin, low-density lipoprotein, and high-density lipoprotein were analyzed. Associations were examined using hierarchically adjusted multivariable linear regression, mediation and moderation were tested and sex-stratified/matched analyses were conducted. While training volume was not associated with endothelial markers, leptin was correlated positively with NO and negatively with diastolic strain rate, suggesting dual vascular actions. fT3 was inversely associated with IMT, indicating a potential protective role in vascular remodeling. Lipoprotein profiles showed no independent associations with vascular parameters. Hemodynamic load, particularly systolic blood pressure, emerged as the dominant determinant of arterial stiffness. Sex-specific differences across biomarkers and vascular indices support a multifactorial model: in active youth, vascular phenotype reflects hemodynamics, body composition, and endocrine–metabolic signals more than training; longitudinal mechanistic studies should clarify causal pathways and guide individualized cardiovascular risk profiling.

Maximal aerobic power (V̇O₂peak) in youth depends on hemoglobin (Hb)—mediated oxygen transport. While sex- and age-specific patterns are established in untrained cohorts, further research is needed in competitive adolescent athletes. We studied 124 young athletes matched by age and sex (62 boys, 62 girls; 10–16 years). Hb was measured from fasting blood samples, and V̇O₂peak was determined via cardiopulmonary exercise testing (CPET). Boys showed higher Hb than girls (14.43 ± 0.85 g/dL vs. 13.6 ± 0.74 g/dL; p < 0.001) and a significant age-related increase (B = 0.29, p < 0.001), whereas girls remained stable. V̇O₂peak was also higher in boys (50.03 ± 6.18 mL/min/kg, p < 0.001). Regression analysis identified Hb as a strong predictor of V̇O₂peak (β = 0.40, p < 0.001). These findings demonstrate that classical developmental Hb trajectories persist in highly trained youth and confirm Hb as a key determinant of aerobic power. Monitoring hematological status, particularly in female athletes, is essential for optimizing performance and development.

Resting antioxidant enzyme activity in youth athletes may reflect stable individual redox characteristics and developmentally modulated plasticity. This 12-month longitudinal analysis from the MuCAYA^plus study examined the tracking of superoxide dismutase (SOD) and glutathione peroxidase (GPX) in 69 trained athletes aged 10–17 years. Participants underwent repeated assessments of antioxidant enzyme activity, training exposure, body composition, and hematological parameters. Longitudinal tracking was evaluated using Pearson correlation and intraclass correlation coefficients, while change-score regression models tested whether changes in training exposure, growth-related variables, sex interactions, and hematological parameters predicted changes in SOD or GPX. In exploratory analyses, cluster-based redox phenotype stability was assessed using agreement statistics. Over 12 months, SOD decreased whereas GPX increased. GPX showed substantial tracking (r = 0.714, p < 0.001; ICC = 0.683), while SOD showed no meaningful tracking (r = 0.057, p = 0.644; ICC = 0.053). No statistically supported associations were detected between changes in training-exposure or growth-related measures and enzyme changes. Exploratory erythrocyte-related associations were observed for SOD, whereas leukocyte and platelet changes were unrelated. Cluster-based SOD/GPX phenotype analyses were not robust. These findings are compatible with a comparatively stronger trait-like component for GPX and greater state-like variability for SOD.