Shannon's health and fitness blog

The myth that just won’t die!

“Keep your target heart rate in the fat-burning zone.”  We hear this phrase used all the time.  We hear it in the media, we see it on cardio machines, and we even hear “fitness professionals”  using it, as if working out at high intensities is a bad thing!  So what is the fat-burning zone anyway?  The fat-burning zone is the heart rate range an individual should be exercising at to burn the most fat.  It is considered to be 60-65% of a person’s maximum heart rate (MHR).  The idea behind this theory is that if a person works out at a low to moderate intensity, they will be burning most of their calories from fat. 

While it is true that a higher percentage of calories burned come from fat at lower exercise intensities, this does not necessarily mean a person will burn more fat this way.  Working at higher intensities (80-85% of MHR) burns so many more total calories, that a person will end up burning more fat even though the percentage of fat calories burned is lower.  Think about it-have you ever seen fat high level runners or triathletes?  They work out at high intensities many days of the week.

Here is an example:

Low intensity exercise (60-65% MHR)

  • Total calories expended per minute = 4.86
  • Fat calories expended per minute=2.43
  • Total calories expended in 30 minutes=146
  • Total fat calories expended in 30 minutes=73
  • % of fat calories burned=50%

High intensity exercise (80-85%MHR)

  • Total calories expended per minute=6.86
  • Fat calories expended per minute=2.7
  • Total calories in 30 minutes=206
  • Total fat calories expended in 30 minutes=82
  • % of fat calories burned=39.85%

As you can see, the higher intensity exercise burned 60 more total calories and 9 more fat calories than lower intensity exercise, even though the percentage of fat burned is higher in the low intensity exercise.

Lower intensity workouts are great if you have 1.5-2 hours to run or bike.  If your workouts are shorter, opt for a higher intensity one!


December 11, 2009 - Posted by | Personal training

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