Exercise and oxidative stress: significance of antioxidants with reference to inflammatory, muscular, and systemic stress.
Many studies have demonstrated that intense muscular work generates considerable amounts of reactive oxygen species (ROS). In order to prevent oxidative stress, the body contains a large number of nonenzymatic and enzymatic antioxidants that either prevent ROS formation or scavenge radical species. Oxidative stress can lead to damage or destruction of cellular macromolecules such as lipids, proteins, and nucleic acids. Therefore, oxidative stress has been associated with decreased physical performance, muscular fatigue, muscle damage, and overtraining. It has been hypothesized that the body's physiological amount of antioxidants is not sufficient to prevent exercise-induced oxidative stress and that additional antioxidants are needed to reduce oxidative stress, muscular damage, or overshooting inflammation. However, some but not all investigations have demonstrated oxidative stress following physical exercise, and also, findings concerning the role of antioxidants in reducing oxidative stress are equivocal. In addition, a clear association between the amount of exercise-induced muscular, metabolic, hormonal, or inflammatory stress and levels of antioxidant vitamins could not be established consistently. Therefore, although the theoretical background may be sound, there is no scientific evidence to recommend increased quantities of antioxidants to physically active people exceeding the amount provided by a healthy, balanced nutrition.