How does exercise improve health over the long term and modestly extend healthspan? One of the important mechanisms is increased autophagy, the collection of cellular maintenance processes that are provoked into action by various stresses. Heat, lack of nutrients, and the oxidative molecules generated during the hard work of exercise are all sufficient to trigger greater autophagy for some period of time, continuing even after the stress has ended. This sort of stress response is an important component of near all of the methods demonstrated to somewhat slow aging in laboratory species. Sadly it isn't anywhere near as effective at extending life span in longer-lived species such as our own. Nonetheless, the benefits of exercise are both highly reliable and essentially free. It would be foolish to skip them given that cost-benefit equation.
Researchers have found that a lack of muscle stimulus due to a surgically induced sciatic nerve injury in rats resulted in a buildup of inadequately processed proteins in muscle cells and consequently led to muscle weakness or wasting. This buildup was caused by the impairment of autophagy, the cellular machinery responsible for identifying and removing damaged proteins and toxins. The researchers demonstrated that physical exercise can keep the autophagic system primed and facilitate its activity when necessary, as in the case of muscle dysfunction due to the lack of stimulus. The degenerative processes caused by a lack of muscle stimulus were found to be delayed in rats that had been subjected to a prior regime of aerobic exercise training.
"Daily exercise sensitizes the autophagic system, facilitating the elimination of proteins and organelles that aren't functional in the muscles. Removal of these dysfunctional components is very important; when they accumulate, they become toxic and contribute to muscle cell impairment and death. Imagine the muscles working in a similar manner to a refrigerator, which needs electricity to run. If this signal ceases because you pull the plug on the fridge or block the neurons that innervate the muscles, before long, you find that the food in the fridge and the proteins in the muscles will start to spoil at different speeds according to their composition. At this point, an early warning mechanism, present in cells but not yet in fridges, activates the autophagic system, which identifies, isolates and 'incinerates' the defective material, preventing propagation of the damage. However, if the muscle does not receive the right electric signal for long periods, the early warning mechanism stops working properly, and this contributes to cell collapse."