The generation of reactive oxygen species (ROS) is a perpetual biological process in eukaryotic cells. Oxidative stress has been defined as an imbalance between oxidants/antioxidants, prompting damage and death. An increase in macromolecule oxidation has been demonstrated after both aerobic and anaerobic exercise of sufficient intensity. The generation of reactive oxygen and nitrogen species (RONS) such as singlet oxygen, superoxide radical, hydroxyl radical, and peroxynitrite occurs as a consequence of normal cellular metabolism and is increased under conditions of physical stress such as prolonged exercise. There is some evidence that resistance exercise can also induce oxidative stress and generation of free radicals akin to those observed during prolonged aerobic and anaerobic exercise.