The basic result (old people who walk faster live longer than old people who hobble around) shouldn't come as a surprise at all: if you see two 75-year-old women at the mall, and one breezes by you like she has somewhere to be while the other shuffles past slowly, and you had to bet on which person had longer to live, you'd pick the fast one.

The interesting part is how strong the result is: "Predicted survival based on age, sex, and gait speed was as accurate as predicted based on age, sex, use of mobility aids, and self-reported function or as age, sex, chronic conditions, smoking history, blood pressure, body mass index, and hospitalization."

That's pretty remarkable. For a given age and sex, all of a person's headline medical information, taken together, is as good an indicator of longevity as their walking speed is.