At 8 months, when their sedentary lab mates were bald, frail and dying, the running rats remained youthful. They had full pelts of dark fur, no salt-and-pepper shadings. They also had maintained almost all of their muscle mass and brain volume.

…

At 1 year, none of the exercising mice had died of natural causes.

…

The researchers were surprised by the magnitude of the impact that exercise had on the animals’ aging process, Dr. Tarnopolsky said. He and his colleagues had expected to find that exercise would affect mitochondrial health in muscles, including the heart, since past research had shown a connection. They had not expected that it would affect every tissue and bodily system studied.