Oxidative stress and antioxidant enzyme activities in elite female Turkish cross-country skiers

Abstract

Background Oxidative stress-related processes contribute to exercise physiology through redox-sensitive signaling, yet when oxidant production exceeds antioxidant buffering, oxidative modifications may be reflected in circulating biomarkers. Evidence in elite female endurance athletes remains limited, particularly in cross-country skiers, and interpretation should be restricted to biomarker-level descriptions within the constraints of cross-sectional designs. Methods This cross-sectional comparative study included 17 elite female cross-country skiers and 17 age- and BMI-matched sedentary women (15-20 years). Following a 10-12 h overnight fast, participants attended the laboratory between 07:00 and 09:00 a.m.; venous blood was collected under standardized resting conditions. Serum catalase (CAT) activity, total glutathione (GSH), and TBARS-derived malondialdehyde (MDA) were quantified using spectrophotometric methods. Between-group differences were tested using the Mann-Whitney U test, with effect sizes expressed as Cliff's delta (delta) and 95% confidence intervals. Within-group associations among CAT, GSH, and MDA were examined using Spearman correlations (rho). Results Compared with controls, skiers showed higher CAT activity (p < 0.001; delta = 0.765, large) and higher GSH concentrations (p = 0.006; delta = 0.554, large), while TBARS-derived MDA was lower in skiers (p < 0.001; delta = -0.848, large; indicating higher values in controls). Within the skier group, CAT and GSH were moderately correlated (rho = 0.57, p = 0.017), whereas no significant CAT-GSH association was observed in controls. No significant correlations were detected between CAT and MDA or between GSH and MDA in either group (all p >= 0.05). Conclusions Elite female cross-country skiers exhibited robust between-group differences in selected circulating redox-related biomarkers at rest, characterized by higher CAT and GSH and lower TBARS-derived MDA relative to sedentary women. These findings describe biomarker-level group separation and should be interpreted as association-level observations without causal attribution, claims of systemic redox homeostasis, or direct inference of training adaptation, recovery, or performance effects (ClinicalTrials.gov identifier: NCT07181889, Date 2025-09-12).