The Question: I want to burn fat (and get rid of that layer of flab that's covering my abs). Should I work out at a low intensity?
The Expert: Mike Donavanik, C.S.C.S., C.P.T., personal trainer and creator of Extreme Burn: Ripped
"To be 100 percent honest and blunt, the fat-burning zone is bull****," Donavanik says. "It's been so badly misconstrued and misinterpreted—it's like a drunken game of telephone."
Here's where that game began: During low-intensity activities, people burn a higher percentage of calories from fat than calories from glycogen (a.k.a. your muscles' stored carbs). And during high-intensity activities, people burn more calories from glycogen than from fat, Donavanik says. "The idea of the 'fat-burning zone' takes that fact and essentially says, 'If you want to lose fat, why work hard? You're only going to burn carbohydrates. And you want to burn fat, right? So, just take it easy and burn more fat."
However, even though low-intensity exercise burns a better ratio of fat to carbs, high-intensity exercise burns way more calories—including those from fat.
Let's tease this out a bit: If you dilly-dally your way through 10 minutes of low-intensity exercise, you'll burn 60 calories from fat and 60 from carbs. On the flip side, if you crank out 10 minutes of high-intensity exercise, you'll burn 80 calories from fat and 120 from carbs, he says. While that's a lower ratio of fat to carbs, it's still more fat—and calories—burned, which is the bottom line when it comes to weight loss. So who cares if you burn some extra carbs while you're at it?
Plus, hitting it harder can help you burn more calories even after your cooldown. Research from the Human Performance Laboratory at Appalachian State University suggests that completing a high-intensity workout can up your metabolic rate for 14 whole hours. (Check out seven more tricks to boost your metabolism.)