FIG. 6.

The free radical-dependent aging theory is well accepted, and it is clearly demonstrated that the extent of oxidative damage increases in the last quarter of the life span. However, it is also clear that the oxidative modification of lipids, proteins, and DNA is well detectable even at a young age, and this could indicate that a moderate level of oxidative damage is not dangerous to cells; moreover, it even can be necessary. On the other hand, significant elevation of oxidative damage at an advanced age is associated with increased incidence of a wide range of diseases and impaired physiological function. Regular exercise has been shown to attenuate the age-associated increase in oxidative damage, and it also attenuates the deleterious effects of aging on organ function (To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars.)