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What is the Best Fat Burning Zone and Heart Rate?

The body does burn a higher percentage of calories from fat in the 'fat burning zone' or at lower intensities.  But, at higher intensities, you burn a greater number of overall calories which is what you should be concerned about when trying to lose weight. The chart below details the fat calories expended by a 130-pound woman during cardio exercise:

  Low Intensity - 60-65% MHR High Intensity - 80-85% MHR
Total Calories expended per min. 4.86 6.86
Fat Calories expended per min. 2.43 2.7
Total Calories expended in 30 min. 146 206
Total Fat calories expended in 30 min. 73 82
Percentage of fat calories burned 50% 39.85%

From The 24/5 Complete Personal Training Manual, 24 Hour Fitness, 2000

In this example, the woman burns more total calories and more fat calories at a higher intensity. This isn't to say that low intensity exercise doesn't have it's place. In fact, endurance workouts should be a staple of a complete fitness program along with shorter, higher intensity workouts or even interval workouts which are a great way to burn calories and build endurance.  To figure out your own intensity levels, start by calculating your target heart rate zone. 

What is Your Target Heart Rate?

In order to figure out which zone you're in, you first need to figure out what your own target heart rate is. You can do this by using the Karvonen Formula. You can also use any number of target heart rate calculators to get your heart rate zone, but many of them do not incorporate your resting heart rate (which makes it a bit more accurate).

Below is an example of the Karvonen formula for a 23 year old person with a resting heart rate of 65 beats per minute (*to get your resting heart rate, take your pulse for one full minute.):

220 - 23 (age) = 197
197 - 65 (resting heart rate) = 132
132 * 65% (low end of heart rate) OR 85% (high end) = 85.8 OR 112.2
85.8 + 65 (resting heart rate) = 150 112.2 + 65 (rhr) = 177
The target heart rate zone for this person would be 150 to 177

For this person to work in his 'fat burning' zone, he would need to stay around 150 beats per minute or lower. To work within his 'cardio' zone, he would need to work at 150 bpm or higher.