Free radical can be defined as a molecule or molecular fragments containing unpaired electron in the outer orbital, which react with nearby molecules to get stability. There are two types of them in the body: oxygen free radicals and nitrogen free radicals. Our body has an antioxidant defense system which prevents accumulation of these radicals. There is a balance between free radical production and antioxidant defense system. Excessive free radical production or weak antioxidant system leads

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... oxidative or nitrosative stress. Diabetes mellitus is one of most important diseases that show cell injury due to oxidative and nitrosative stress in many tissues especially arteries. It causes atherosclerotic plaques in arteries by induction of inflammation, increasing the adhesive molecule expression, extravasation of circulating inflammatory cells, over-expression of some transcription factors, and fat deposition in the wall of arteries. Exercise is one of the main factors that influence production of free radicals and performance of antioxidant defense system. Although strenuous and acute exercise induces oxidative stress by increasing production of free radicals, but regular moderate exercise causes resistance against oxidative and nitrosative stress by potentiating antioxidant defense/repair systems. It appears that regular exercise accompanied by changes in life style is effective in reducing complications of diabetes, especially in prevention of atherosclerosis.