Ask A Coach: Fat-Burning Zone

Last week, we received a question about the mysterious "fat-burning zone."  Coach Leanne answers below. Send your running questions to us!

Hi! Will I burn more fat if I remain at 60%-75% of my heart rate?

This a great question about an often confused concept. Yes, your body uses fat as the primary fuel source at a lower intensity, but no, if your goal is to lose fat, this is not the most effective way. It's helpful to understand a few things

  1. At different intensities (or heart rate zones) your body taps into different fuel sources. BUT low-intensity, "fat-burning" workouts at 65% of your Heart Rate Max will not necessarily burn weight gained by eating, say, buttery foods.
  2. There is a difference between Absolute Fat Burn and Relative Fat Burn. Although you will burn a higher percentage of fat (relative) than glycogen at lower intensities, your total (absolute) amount of fat burned during a high-intensity workout will be higher, because your overall calorie burn is higher. (see diagram below)
  3. If your goal is losing weight, burning more calories is most important than specifically burning fat.
  4. It's not just about the calories / fat you burn during the workout - it's also about the after burn effect. Excess post-exercise oxygen consumption (EPOC), also known as after burn, refers to the process your body uses to return to homeostasis (normal) after a tough workout. When you work out at a low intensity, there is very little after burn, meaning your body burns very few calories after the workout itself is over. With a high-intensity workout, there can be a huge after burn, meaning you continue to burn calories and contribute to weight loss after you've left the gym.
 
Understanding Absolute vs. Relative Fat-Burn, via builtlean.com

Understanding Absolute vs. Relative Fat-Burn, via builtlean.com

 

In short, there is no reason to stay in a low-intensity, 65% HR Max zone if your goal is to lose fat. Below are a few articles that go into a bit more detail. Thanks for sending your question in!

From Men's Health, "Instead, he advises clients to focus the majority of their efforts on generating a calorie deficit. “You may burn a little more fat during exercise, but if a calorie deficit isn't present, then it will all even out in the end you won't lose much fat at all.” In lower intensity programs, the overall calorie burn during a workout will be lower than a high intensity workout - regardless of whether those calories come from fat or carbohydrates.'" Read more...

From BuiltLean.com, "While low intensity exercise certainly has its place within an exercise regimen, relying on exercise in the fat burning zone to burn fat is not an efficient approach. Contrary to popular belief, getting up early in the morning to do low intensity cardio on an empty stomach will not help you lose more body fat versus other more intense methods. For busy people, interval training and circuit training workouts are substantially more efficient to help you burn far more calories in much less time, and burn more fat in the process." Read more...

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