
While you're walking, think about how hard you're pushing yourself. On an exertion scale from 0 to 10 (with 0 being "easy" and 10 being "very, very difficult") you want to go beyond the 3 or 4 most people settle on. Crank it up to a 6 or 7 to get fat-burning engines revved and running. How do you know you're there? Do the talk test. You should be walking swiftly enough so that you can talk a little but find it difficult to carry on a conversation. If you're walking alone, it should be a struggle to sing along with your iPod for more than a few verses.