Enzyme-Specific Redox Stability and Plasticity in Trained Youth Athletes: Longitudinal Analysis of SOD and GPX.

Resting antioxidant enzyme activity in youth athletes may reflect stable individual redox characteristics and developmentally modulated plasticity. This 12-month longitudinal analysis from the MuCAYAplus 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.