This CrossFit Workout of the Day (WOD) burns an average 13 calories per minute, according to scientists at Kennesaw State University.
It's effective because it pairs three exercises—5 pullups, 10 pushups, and 15 air squats—that work different major muscle groups, and you do as many rounds as possible in 20 minutes.
So if you're in amazing condition, you can go all-out for each one, without slowing down or stopping to recover in between.
If you're somewhat less than amazing (read: like most people), you simply rest when needed. For example, you don't move on to the pushup until you've completed 5 reps of the pullup, even if you have to stop and start.
"Any routine that takes you from standing, down to the ground, and back up to standing again is an amazing calorie burner, because it really spikes the heart rate," says John.