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My heartrate is 65 at rest and top heartrate i can get while biking is 191. My goal is to burn some extra fat so i try to get i the 60%/70% zone for optimal fat burning.

Now i find there are 2 ways to calculate this zone.

  1. Take 60% and 70% of your max rate: 114-134
  2. (60% or 70%) * (max Hr - rest Hr) + rest Hr) 140-153

These result turn out very different but which one is correct? Or how should i interpret these?

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There are several other methods as well including various "field tests", blood testing, and other formulas like philmaffetone.com/180formula.cfm. Your mileage may vary. –  Ryan Miller Sep 5 '13 at 13:43
    
You may also be interested in learning about Metabolic Efficiency Training fuel4manceblog.blogspot.com/p/store.html –  Ryan Miller Sep 5 '13 at 13:44
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1 Answer

The reason for the difference in these two results is that the second formula that you cite is not a direct heart rate zone, but it rather is an assessment of heart rate reserve (HRR) (Karvonen formula).

HRR is the difference between your maximum heart rate (MHR) (Either predicted or measured) and your resting heart rate. The theory is that as you get fitter, your MHR will increase, and your RHR will decrease, and as a result your HRR zones will change to reflect your fitness level. In reality, the Karvonen was a bad sample, based on less than 10 people if I remember right, and it doesn't take into consideration VO2 values either.

I am not a big fan of exercising according to heart rate zones, for the simple reason that there are too many variables that can affect the heart rate in various ways. For example, take your MHR, and your calculated zone of 114-134. Today you were tired when you woke up, so you have coffee for a change, and you are also dehydrated and tense from work. All of these combine to raise your normal heart rate by 10 beats per minute overall. Now when you workout, you are probably not working as hard as you think you are, because your HR is elevated for reasons unrelated to your exercise level.

Your best bet is just to pick one method, calculate your zone and use that. As long as you are consistent, you should see results. The body is a very complicated system, and lumping things in by zones and generic predicted formulas generally has mixed results, i.e. it works for some but not others.

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