Myth: The “Fat Burning” Zone
“It was invented to sell you heart rate monitors, treadmills, and other ‘science-backed’ nonsense”

These days you’re bombarded by so much marketing that it’s hard to separate fact from fiction. One of the myths that drive me crazy is exercising in the “Fat Burning Zone,” which in turn gives you better results. Just in case you want to stop reading, it doesn’t – not even close, nothing replaces old-fashioned hard work. With all things in life, wouldn’t it be nice if we could get great results by only giving a B, C or D-level effort?

Let’s start with what the “Fat Burning Zone” is. If you’ve ever stepped on any cardio equipment, like a treadmill or stair stepper, or went to one of those [insert color here] theory fitness facilities, or went to a group fitness program that required the use of a heart rate monitor, then you’ve probably seen the colored graph with numbers or percentages that shows the relationship between heart rate and fat burning. This so-called, highlighted sweet spot is known as the “Fat Burning Zone,” and there is research to support it. “So the ‘Fat Burning Zone’ does exist? While there is some truth to it, you have to take it within context.

So where’s the truth? Well, it’s true that between 60%-80% of heart rate max, most people do utilize the highest amounts of fat for fuel. Whereas working above that zone you’ll use primarily carbohydrates as an energy source, and below that zone you still use body fat, but just not as much. Right about now, you’re probably confused and wondering why you shouldn’t workout in this zone and the answer is, “Excess Post-exercise Oxygen Consumption,” also known as EPOC.

What is EPOC? EPOC is also referred to as Oxygen Debt, essentially how much oxygen is required to return your body to homeostasis, otherwise known as your Resting Metabolic Function – where you were before you exercised. This process or physiological effect is how your body continues to burn MORE calories well after you’ve finished your workout. Most importantly, this process of returning to your Resting Metabolic Function can take 24-48 hours, and even after some workouts up to 60-72 hours. To achieve this maximal effect, your workout needs to be intense enough and activities such as a good session of strength training, running sprints, playing pick up basketball, etc., or other activities that causes you to work in anaerobic zones can get you there.

*Let’s put this into a practical example. For simplicity we’ll just say you burn 1 caloric unit per minute (60 per hour) when you’re at your Resting Metabolic Function.

  • 1 Hour Jog: After an aerobic jog your EPOC is elevated where it requires 6 hours to return to homeostasis at 1.5 caloric units per minute (90 per hour), then it returns to normal.
    • Normal Expenditure in 6 hours without jogging: 6 hours x 60 caloric units per hour = 360 caloric units
    • Expenditure with jogging: 6 hours x 60 caloric units per hour x 1.5 EPOC = 540 caloric units
    • Net burn of 180 caloric units more than without exercise
  • 1 Hour High Intensity Workout: After a high intensity workout your EPOC is elevated for 24 hours, at 2 caloric units per minute.
    • Normal Expenditure in 24 hours without High Intensity Exercise: 24 hours x 60 caloric units per hour = 1,440 caloric units
    • Expenditure with high intensity exercise: 24 hours x 60 caloric units per hour x 2 EPOC = 2,880
    • Net burn of 1,440 caloric units more than without exercise
    • A net effect of 1,260 more caloric units than jogging

So where do you burn more body fat overall?

  1. 1 hour of aerobic cardio
  2. 24 hours of elevated caloric consumption post high intensity exercise

Just in case it’s not very clear, the answer for the above question is B. However, I don’t want you thinking heart rate monitors are worthless because they’re not, and in the right hands (someone who can actually interpret the data objectively) it can be beneficial. However, it’s usage as a gauge for working in a “Fat Burning Zone” is a horrible use of a heart rate monitor. Also, I’m not telling you that you should just workout at high intensities and metcon yourself into the ground every day – because I’m not saying that either as there is the variable of post workout recovery. But why you shouldn’t high intensity metcon every day is a whole different blog entry that I’ll write about another time. Just in case you’re curious, all modes of fitness have its place, and if you’re sprawled out on the ground gasping for air after a metcon every day, then that’s not good either!

*PLEASE NOTE: The aforementioned example is just an example. Results and data from individual to individual are different and will vary.