By Lucy Danziger, SELF Editor-in-Chief YAHOO.Health.ratingWidget.init("rate-form","thumb-rate",0,0,"blog entry"); I love my long training runs, but most days carving out more than an hour to work out just isn't in the cards. And when my schedule is really crammed, shoehorning a sweat session seems next to impossible. Luckily, the fantastic fitness team at SELF let me in on a little secret: You can get an hour's worth of fitness and calorie burning in 20 short minutes. Yes, I was skeptical at first, but this fat-blasting routine is as ultraeffective as it is speedy, and the secret lies in high-intensity spurts of energy. Here's how to do it: • Pick any cardio you like (running, swimming, the elliptical trainer). Warm up for 2 minutes at a moderate...