Fit ‘N Healthy Column: The truth behind the “Fat Burning Zone”


By Mary Rigney, fitness expert & CrossFit Rockwall owner. Do you know anyone who jogs for miles every week and cannot lose weight? The people you see who religiously do 30-60 minutes on the elliptical machine look about the same as they did months ago, don’t they? Why aren’t they getting fitter? And how can others get such amazing results with workouts that last less than 20 minutes?

We are often asked how short, intense workouts can provide better fat-loss benefits than traditional long duration, low-power workouts in the so-called “Fat Burning Zone.”

The “Fat Burning Zone” is supposed to be exercise done between 55% and 65% VO2 max. That means, working at slightly more than half (55-65%) of your aerobic capacity (V02 max). In other words: slow and easy. Jogging or other slow-paced exercise on “cardio” machines is often proclaimed to be the most efficient way to lose weight. But, is it?

We’ve all seen the charts on cardio machines and on the walls of traditional gyms that erroneously show the most effective fat burning exercise occurs when the heart rate is in the range of 55% to 65% of its maximum. These charts are in exercise science books everywhere. This inaccurate obsession is based on research which shows that when we exercise at 50% of VO2 max (low intensity cardio) our body draws about 50% of its energy from stored fat, and that when we go to higher intensity, 70% or more of VO2 max , we only draw about 33% of our energy from stored fat. All of this is true (Romijn et al and other researchers have come to similar conclusions). However, we burn more calories overall with a more intense workout. A smaller percentage of a bigger total can be better than a larger percentage of a smaller total. Would you rather have 1% of a million dollars, or 50% of a thousand dollars?

Now, if you go on an all day hike or four-hour bike ride, you will burn a significant amount of body fat (although there are other health issues that go along with “chronic cardio”). But if you don’t have 4-8 hours every day to work out, high intensity is the way to go. Obviously, “high intensity” is a different value for everyone, and you have to find an intensity that is safe for you. Your mother’s high intensity will be drastically different from a college athlete’s high intensity; it’s all relative. But she can still workout at an intensity level that is safe and beneficial to her.

There is more to the story than just the amount of fat burned during the exercise session. High intensity exercise raises your metabolism for a longer period of time post exercise than slower paced aerobics. After finishing an intense (but short) workout, your metabolism may be higher for up to 14 hours afterwards. But at the end of a slow, steady jog, your body will be back to its steady state within an hour and you will be right back where you started. A higher metabolism post workout means you are burning more calories, even if you’re sitting at a desk most of the day. Not to mention, you will have significantly more energy!

More vigorous workouts will give you greater fat loss and better overall fitness than long and slow workouts. If you have limited time to work out, interval training will help you reach your goals faster. However, you should never jump right into a high intensity exercise program. You must begin by learning the techniques and maintaining a consistent workout schedule. Only then can you begin to gradually increase the intensity level of your workouts. Your body will need time to adapt to the stimulus, as it is vastly different from watching TV on a stair climber. But, you will not be disappointed with the results!

For more info, call 972-454-XFIT (9348).

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