This paper illustrates one the reasons why exercise is good for healthy longevity, diving into the mechanics of damage to mitochondria and its role in aging: "Mitochondrial dysfunction is commonly thought to result from oxidative damage that leads to defects in the electron transport chain (ETC). ... we highlight new research indicating that there are early changes in mitochondrial function that precede ETC defects and are reversible thereby providing the possibility of slowing the tempo of mitochondrial aging and cell death. ... Increased mitochondrial uncoupling - reduced adenosine triphosphate (ATP) produced per [oxygen molecule] uptake - and cell ATP depletion are evident in human muscle nearly a decade before accumulation of irreversible DNA damage that causes ETC defects. New evidence points to reduction in activators of [mitochondrial] biogenesis [and] to degradation of mitochondria allowing accumulation of molecular and membrane damage in aged mitochondria. The early dysfunction appears to be reversible based on improved mitochondrial function in vivo and elevated gene expression levels after exercise training." The more time you have before needing to benefit from the mitochondrial repair therapies of the future, the greater the chance those therapies will exist when you need them.