Aim: The purpose of this study was to investigate the relationship between oxidative stress, antioxidant defense system markers and VO2max, one repetition maximum (1RM), and relative strength in trained and untrained men. Methods: Sixteen apparently healthy volunteers (trained N.=8; untrained N.=8; age: 27.25±5.5 years) participated in this study. To elicit blood oxidative stress, all participants performed the leg extension resistance exercise at progressive intensities: 1) 1×17 reps at 50% of 1RM; 2) 1×14 reps at 60% of 1RM; 3) 1×12 reps at 70% of 1RM; 4) 2×5 reps at 80% of 1RM; 5) 3×3 reps at 90% of 1RM, with 5 minutes of rest between intensities and 90-120 seconds of rest between sets. The RE intensities were standardized for total volume. Blood samples were drawn before (PRE), immediately post each intensity (T50%, T60%, T70%,T80% and T90%), and after (30 minutes post =T30 min, 60 minutes post =T60 min and 24 hour post =24 h) the RE in order to analyze lipid hydroperoxide (LHP), protein carbonyl (PCO), total glutathione (GSH) and superoxide dismutase (SOD). Results: A significant correlation was found between VO2max and Pre-LHP and Pre-PCO concentration, and between VO2max and T24h GSH concentration. A significant correlation was also found between all GSH measures (except PRE) and 1RM and relative strength. Furthermore, SOD and PCO levels were significantly correlated to strength variables. Conclusion: It was determined that both aerobic exercises and anaerobic or resistance exercises - by increasing muscle mass and power - are important to improve the antioxidant defense capacity.