Should I be working out in the Fat Burning Zone?

By Liz Neporent

Virtually every piece of cardio equipment at the gym has a slow-paced "fat burning" program on the display panel that promises to help you stay "in the fat burning zone." If you are trying to lose weight, cover it with a towel and ignore it. Workouts that focus on the fat burning zone are a relic of the persistent yet outdated belief that long, slow workouts are always better for weight loss than faster, shorter workouts. But you can file that along with other fitness myths you should ignore: The best fat burning workout plan is simply the one that burns the most calories.

Like many myths, the so-called fat burning zone is based on a grain of truth: At slower speeds, your body's primary fuel source is fat, whereas at higher intensities, usually at a rate of perceived of exertion (RPE) of 7 or higher, you primarily draw on the carbohydrates that are circulating in your bloodstream or stored in your muscle. Misguided exercisers often reason that using higher percentages of fat as fuel must translate into quicker fat loss. The reality is, the more calories you burn, the closer you inch toward your weight-loss goals, regardless of what type of fuel your body uses for energy.

Here's a quick example to illustrate the point. It involves some arithmetic so I'll walk you through it. Let's say you spend a half an hour on a treadmill doing a casual stroll as you watch videos and yada yada with the person on the next mill over. You might burn 150 calories with this routine, about 80 percent of them from fat. That's a total of 120 fat calories burned.

Now let's say you spend 30 minutes doing a gear-grinding, booty-kicking spin class with tons of sprints, jumps and hills thrown in to dial up the intensity. In this scenario, you destroy 300 total calories with approximately 50 percent—150 calories—coming from fat. Even if I lost you on the number crunching, it should be clear why the second workout is superior for calorie burn (twice as much!), fat burn and weight loss.

That's not to say that low-and-slow workout sessions don't have their place in your exercise and weight loss plan. They are easy on your body and you can do them day after day; they are the ‘base' of your exercise program. Overdoing high intensity workouts leads to burnout, soreness and injuries (stretching has lots of body benefits, including greater flexibility, but in most cases it doesn't prevent injuries). And if you're sidelined from exercise entirely then you certainly won't burn any calories—from fat or otherwise.

I recommend doing two high intensity, one or two moderate intensity (60 to 75 percent of maximum effort) and one to three low intensity workouts a week. Also, if you're a serious athlete training for competition, then it is a good idea to undergo a complete physiological workup in a sports medicine lab to find out exactly which fuels you burn at exactly which heart rates; this will help make your training plan more precise and sharpen your competitive edge.