The purpose of this study was to determine the changes of oxidative response and exercise-induced muscle damage after two different resistance exercise protocols. Whether training with low or high intensity resistance programs cause alterations in the activities of lipid peroxidation, nitric oxide (NO_x), and creatine kinase (CK) activity in human plasma was investigated. Twenty untrained males participated into this study. Ten of the subjects performed high intensity resistance (HR) exercise circuit and the rest of them performed low intensity resistance (LR) exercise circuit of 4 different exercises as a single bout. Venous blood samples were drawn pre-exercise, immediately after the exercise, and at the 6^th, 24^th, 48^th and the72^nd hours of post-exercise. Samples were analyzed for markers of muscle damage (CK), lipid peroxidation (MDA) and NO_x. NO_x production increased in HR group (p < 0.05). The MDA response to the two different resistance exercise protocol in this study caused a significant increase between pre and post-exercise values in both groups (p < 0.05). Also, there was a significant difference in the MDA level between the two groups in post-exercise values (p < 0.05) and higher values were observed in HR group. CK activities showed a significant increase in all post exercise values (p < 0.05) of both groups but there were no difference between HR and LR groups. These findings support that high intensity resistance exercise induces free radical production more than low intensity resistance exercise program.

• High intensity resistance exercise caused increases in NO, MDA and CK levels.

• Light intensity resistance exercises increased MDA and CK levels but did not affect NO levels.

• Damage arose during resistance exercises may be related to the level of resistance applied.