Reactive oxygen species are produced by body cells, and this is a consequence of aerobic metabolic reactions. Oxidative stress is defined as an imbalance between the body antioxidant defense and production of reactive oxygen species. Exercise is one of the factors that disrupts the balance between ROS and the antioxidant system. The ROS production level depends on the exercise strength and intensity. To improve the mechanism against exercise-induced oxidative stress, use of antioxidant supplements is quite common in athletes. But it is not clear whether an increased antioxidant consumption is needed during periods of training, including strenuous exercise. Researchers have demonstrated that ROS have a beneficial role in the cell metabolism, such as the activation of cell signal transduction pathway, and according to the hormesis theory, oxidative stress at low level is required to regulate endogenous oxidant defenses. Studies are conflicted about whether an increased antioxidant intake (with antioxidant-rich foods or antioxidant supplements) is necessary after exercise, and which way provides the most adequate amount of antioxidant intake for the human body mechanism.