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Fat-Burning Zone: Fact or Myth?

 

Question: On all of the cardio machines at the gym, I see mention of a Fat-Burning Zone. I hear that if your heart rate exceeds this, you won't burn as much fat. Is that true?


Answer: This is one of those misconceptions that should be put to rest once and for all. The "fat-burning zone" idea got its start about 15 years ago, when scientists reported that during high-intensity aerobic exercises, the body burned mostly stored carbohydrates for fuel, as opposed to burning stored fat as it did during lower-intensity activity.
Exercise instructors took the news and ran, leading the charge for low-intensity "fat-burning" classes. Obviously, these classes didn't end being the magic bullet for weight loss. Here's why:

It's true that the body burns a higher percentage of calories from fat during more mellow exercise like walking and easy cycling. But, when you pick up the pace for a higher-intensity cardio workout, you burn a greater number of overall calories (which should be your focus for weight loss) and subsequently just as much total fat.

Let’s take me for example. As of this post I am 280 pounds; let’s compare a fairly easy walk and a high-intensity jog. After 1 hour, I would have burned the following in total and fat calories:

Busting the myth
  Moderate Intensity
(60-70% max heart rate)
High Intensity
(70-80% max heart rate)
Total calories burned 538 806
% of fat calories burned 75% 50%
Total fat calories burned 403 403

As you can see, you would burn just as much fat and significantly more calories by working out at a higher intensity. What's more, high-intensity aerobic exercises kick your metabolism into high gear even after you're done working out.

According to Janet Walberg Rankin, PhD, a professor of nutrition at Virginia Tech University,  your body will actually burn more fat during your recovery time after a high intensity workout. Your metabolism also stays revved up five times longer after a vigorous workout than after an easy one. Over time, this can add up to burning an additional 100-200 calories a day.

Of course, this assumes that you are able to maintain the high intensity workout for as long as you can the moderate one. If you are able to walk for an hour but can only jog for a few minutes, you are better of walking. However, what many people forget is that exercise doesn’t have to be all one exercise. In fact, it’s better if there is variations in the routine.

The easiest way to infuse intensity into your existing routine is to sneak some intervals into the aerobic workouts you already do. For example: If you walk now, start by warming up for 5 to 10 minutes, then try picking up your pace and running (so your breathing becomes heavy, but you're not gasping for breath) for 3 minutes, then walk for 3 minutes, and so on. Do this 2 days a week. Before long, the running segments will feel easier, and you'll be a speedier walker, too, which means more calories burned every time you exercise.