Exercise has long been correlated with a longer life, but it’s only recently started to become clear why this might be. Studies, like a new one in the journal Preventive Medicine which found that exercise is linked to longer caps at the ends of chromosomes, have helped flesh this out a bit more. These caps, called telomeres, naturally shorten as we age, with each cell division. People who live a long time have telomeres that are in better shape than those who don’t—but there’s a lot we can do to affect the rate at which they shorten over the years. The team behind the new study looked at data from CDC's National Health and Nutrition Examination Survey, and found that for people who exercised regularly, their telomeres were 140 base pairs longer on average than sedentary people's. Which correlates to being years “younger” than their sedentary peers.