Exercise is associated with increased metabolic demand, which results in an increased formation of reactive oxygen species (ROS). However, regular exercise appears to decrease the incidence of a wide range of ROS-associated diseases, especially those related to lifestyle, such as cardiovascular diseases and type II diabetes, and also age related conditions such as Alzheimer's diseases and some kind of cancers. The preventive effect of regular exercise, at least in part, is due to oxidative stress-induced adaptation. The oxidative challenge-related adaptive process of exercise is probably not just dependent upon the levels of ROS but primarily on the increase in antioxidant and housekeeping enzyme activities related to oxidative damage repair enzymes. Therefore, the effects of exercise resemble the characteristics of hormesis. In addition, it appears that oxidative challenge-related effects of exercise are systemic. Skeletal muscle, liver, and brain have different metabolic rates and functions during exercise, but the adaptive response is very similar: increased antioxidant/damage repair enzyme activity, lower oxidative damage, and increased resistance to oxidative stress, due to changes in redox homeostasis. Hence, it is likely that the beneficial effects of exercise are due to the ability of exercise to produce increased levels of ROS. A sedentary life, which systemically decreases the body's capability to withstand oxidative challenge, increases the vulnerability to numerous physiological and environmental perturbations.
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