You've heard it before: It's best to get 30 minutes of moderate cardio exercise on most days in order to stay healthy and keep your weight in check. But what, exactly, qualifies as "moderate" exercise? Thanks to a recent study, now we know. Researchers from the Prevention Research Center at Yale University measured the energy expenditure of volunteers as they walked on a treadmill and determined that moderate exercise was 92 to 102 steps a minute for men and 91 to 115 steps a minute for women. The experts recommend counting steps with a pedometer until you get a feel for the pace.