Reactive oxygen species include superoxide, hydrogen peroxide, hydroxyl radical, and singlet oxygen. Produced as byproducts of mitochondrial respiration, immune activity, and enzyme reactions.
Mechanism — Damage lipids (peroxidation), proteins (carbonylation), and DNA (oxidation). At low, controlled levels, also serve as signaling molecules — exercise-induced ROS drive mitochondrial biogenesis (a hormetic response). The damage-vs-signaling balance is dose-dependent.
Use case — Endogenous defenses (glutathione, SOD, catalase) matter more than exogenous antioxidants. Train hard, sleep enough, sufficient mineral cofactors (zinc, selenium, manganese), polyphenols from food.
Caveats — High-dose antioxidant supplements can blunt exercise adaptation. Vitamin E + C megadoses underperform whole-food polyphenols in trials. Less ROS isn't always better — context matters.