Should I trust a HRM for calories burned?

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  • DebbieLyn63
    DebbieLyn63 Posts: 2,650 Member
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    I have heard that Timex can greatly overstate calorie burns, especially for women. I have a PolarFT4 and it gives me half the number that my bike computer, and MFP says. Even with the lower number, I find that if I eat back my calories burned, it puts me into maintenance or even gain level.
    In theory, it shouldn't be the case, but in real life for me, that is my experience. So I exercise for cardio and strength, but eat at a calorie deficit for losing weight.

    And I don't need a bunch of people telling me that I am wrong on this. I am only saying what I have found to be true for ME over the past 5 months.
  • DebbieLyn63
    DebbieLyn63 Posts: 2,650 Member
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    If you are this concerned about accurate calories burned through exercise, then you need to know your VO2 Max (which is the amount of oxygen you can process). Higher VO2 Max means a lower heart rate at a given intensity.

    That being said, if you're going this close you're probably doing it wrong :) High performance athletes, body builders, etc may have concerns, but you should be within a couple hundred calories.

    Here's how to determine your VO2 Max and how to use it to determine the calories burned.
    Determine VO2 Max: http://www.shapesense.com/fitness-exercise/calculators/vo2max-calculator.aspx
    Calculate Calories: http://www.shapesense.com/fitness-exercise/calculators/heart-rate-based-calorie-burn-calculator.aspx

    The VO2 info made my eyes glaze over and was a bit confusing. However, the heart rate calculator was really eye-opening!

    Looking back in my exercise diary notes I found a day back in November when I first got my HRM where I rode my bike for 1 hour and my Ave HR was 114
    According to my HRM I burned 394 calories in that hour.
    According to the calculator from that site you suggested-
    It gave me 329 gross calories for a 60 min workout at an ave 114 HR, but the NET cals burned were only 294.

    This certainly explains why the exercise burns I get do not equal the weight loss rate it should, according to the MFP calculators. Before I bought my HRM, I would enter an hour of light cycling and it would say I burned 700 cals!

    So a difference of over 400 calories! If I were eating back those calories, I would be gaining weight!

    I am also glad that I now average around 130 BPM for my workouts. Makes a huge difference.

    I think I will be using that calculator to figure my burns from now on.

    ETA, I actually rechecked my numbers and my HRM gave me 330 gross calories for an hour, so this calculator is almost exact with the PolarFT4!
  • Espressocycle
    Espressocycle Posts: 2,245 Member
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    Maybe take your average heart rate for the exercise and run it through another calculator and see if they match up. If the heart rate is right but the formula the watch uses isn't, that could create a discrepancy.
  • peggymoney
    peggymoney Posts: 126 Member
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    Thanks that was good info, I was looking into buying a hrm soon and heard polar is the way to go!
  • kohlmannj
    kohlmannj Posts: 1
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    Calculate Calories: http://www.shapesense.com/fitness-exercise/calculators/heart-rate-based-calorie-burn-calculator.aspx

    YES!! This is a research-based calculator, and is the best one I've found to be applicable. It still overestimates a bit (due to the assumption of a high VO2 max), but it's pretty close.

    A very, very, very important point though is that the calculator is NOT correct for an average HR below ~60% of your max HR. That is also explained in the research paper that produced the calculator.

    The other point (that DebbieLyn63 highlighted above) is that if you're going to use this as a way to figure out how many calories you can "eat back" (by adding it to your basal metabolic rate) , be sure to use the NET calories burned, not the GROSS calories burned. There's a link to figure that out on the same page as the original calculator listed above.

    HRMs are all over the place, so it's hard to say how accurate yours is compared to any other. It depends on a lot of factors. My advice is to just use it to calculate average HR and exercise time, then plug those numbers in manually to the calculator listed above.

    Good luck!
  • sasu27
    sasu27 Posts: 51
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    It's a Timex one that I bought a few years ago that I just dusted off recently. Better late than never, right?

    I had a Timex Ironman HRM with the chest strap and after getting crazy high readings from just doing simple tasks like cleaning (800 calories in a hour), I returned it and purchased a Polar HRM. There was a 400 calorie difference in the readings (polar reading lower). So for me, no I wouldn't trust Timex.
  • kensgirl2
    kensgirl2 Posts: 21 Member
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    Calculate Calories: http://www.shapesense.com/fitness-exercise/calculators/heart-rate-based-calorie-burn-calculator.aspx

    YES!! This is a research-based calculator, and is the best one I've found to be applicable. It still overestimates a bit (due to the assumption of a high VO2 max), but it's pretty close.

    A very, very, very important point though is that the calculator is NOT correct for an average HR below ~60% of your max HR. That is also explained in the research paper that produced the calculator.

    The other point (that DebbieLyn63 highlighted above) is that if you're going to use this as a way to figure out how many calories you can "eat back" (by adding it to your basal metabolic rate) , be sure to use the NET calories burned, not the GROSS calories burned. There's a link to figure that out on the same page as the original calculator listed above.

    HRMs are all over the place, so it's hard to say how accurate yours is compared to any other. It depends on a lot of factors. My advice is to just use it to calculate average HR and exercise time, then plug those numbers in manually to the calculator listed above.

    Good luck!


    This is what I've started doing! I was going to buy a Polar HRM, but since you all have posted this site, I think I'll save the money and just plug in the numbers from my own. And it WAS an eye-opener! I *knew* that I couldn't've been burning as many calories as my HRM said I was, but dang!!! It made me feel like I was doing something!!!! :mad: But now I have a more realistic place to work from and won't be disappointed when my scale shows me something different than what I thought I had earned. *sigh*

    Thank you all for your input! It is greatly appreciated!!!!!!

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