The Fat Burning Zone is STILL a myth!

The discussion at the gym usually sounds like this, “If you work too hard while doing cardio you’re not going to burn any fat!” All hail the almighty and deceiving “Fat Burning Zone!” I’ve been in the fitness industry for over 15 years and am still amazed this myth continues to exist! Even today, cardio equipment manufactures display low intensity as “weight loss,” on their monitors and numerous personal trainers prescribe it as the best method for fat loss! No wonder confusion still exists! The question is why the misconception?

Specifically the fat burning zone is 50-60% of your maximum heart rate and research has shown that you burn a higher percentage of fat at lower intensities. Thus, the conclusion was drawn that cardio performed at a lower intensity would lead to faster weight loss (i.e. "Fat Burning Zone"). The deceiving part of this theory is the rate of calorie expenditure is often left out, which is more important factor. Besides, fat is still being used at higher intensities and in most cases will lead to more fat calories being burned. For example, the exerciser expends approximately 8 calories/minute on average while training in the fat burning zone, with approximately 50% coming from fat. In contrast, working at 70-80% of max heart rate (Cardiovascular Zone), the exerciser burns 11 calories/minute on average with 40% of fat being used. Here’s the result:

Fat Burning Zone (50-60% of max heart rate)
• Approximately 50% of calories come from fat
• Approximately 8 calories/minute are expended
• 60 minutes x 8 calories/minute = 480 calories
• 50% x 480 calories = 240 fat calories

Cardiovascular Zone (70-80% of max heart rate)
• Approximately 40% of calories come from fat
• Approximately 11 calories/minute are expended
• 60 minutes x 11 calories/minute = 640 calories
• 40% x 640 calories = 264 fat calories

As you can see, the cardiovascular zone yields a higher expenditure of total calories and fat calories. In addition to burning more fat, your fitness levels rise as well. This is key because fitter individuals tend to burn more fat during their workouts and post-workout. Since carbohydrates are the preferred fuel during exercise and there is a limited supply, the body begins to spare carbohydrates (i.e. glycogen sparing) and uses a higher percentage of fat during workouts when fitness levels are higher. Also, after intense exercise, the body has increases in lactic acid, body temperature, breathing, heart rate, and elevated hormone levels. In order to restore equilibrium, higher amounts of oxygen are required, often referred to as Excess Post-Exercise Oxygen Consumption (EPOC). With the higher demand for oxygen, more fuel is required from the body during post workout recovery. And guess what the primary fuel is during this process...FAT!

With all of this being said, there are many benefits to working at higher intensities while doing cardio, but lower intensity workouts should still be implemented 1-2 times per week into your weekly routine at durations of 60-90 minutes. The focus of these workouts should be “active recovery.” Good examples would include a brisk walk/slow run or a long bike ride. These workouts are great for recovery and are mentally refreshing as well.

Overall my purpose of writing this was to dispel the “Fat Burning Zone” myth and provide a better picture for effective cardiovascular workouts. The bottom line...an effective weight loss and fitness program should include both high and low intensity cardiovascular workouts, strength training, and proper nutrition for optimal results.

For my next post, I will discuss target heart rate and outline the “ideal” cardiovascular program.

Stay tuned…