Limitations of HRM Calorie Counts - A Real Life Data Point

The_Enginerd
The_Enginerd Posts: 3,982 Member
edited November 7 in Health and Weight Loss
HRMs are often relied upon to get the most "accurate" calorie counts, but it's important to know their limitations. Azdak has made some excellent posts on the limitations and the reasons, and I recommend searching for his posts if you'd like more background on the subject. In summary, they are not accurate for low intensity activities (such as using one while cleaning or walking) and weight training. They are most accurate for steady state moderate intensity cardio at 60-85% of your maximum HR. They can still be inaccurate even then if not set up properly or the assumptions made are not accurate for you. This is especially true if you have a lower end HRM that does not allow you to set your VO2MAX. With that background out of the way...

I wanted provide some real world experience on how inaccurate an HRM can be when it's assumptions no longer hold. I use a Polar FT40 that has been set up with my VO2MAX using recent race results. On my regular runs, the HRM calorie burn is within 5% of that from running calculators.

Not brought up as often is that HRM calorie burns will be inaccurate in hot conditions. Yesterday, I did a two hour trail run from 2-4 pm in 100ºF heat with almost full sun. My real calorie burn was about 1200 calories. According to my HRM, it was 1750 calories. Why such a big discrepancy? The assumed exertion versus HR relationship no longer held because my HR was significantly higher from my body pumping blood to try to keep me cool. The HRM has no way of knowing this, it is only reading my HR.

Lesson: Take those HRM calorie counts with some grains of salt.

Replies

  • stumblinthrulife
    stumblinthrulife Posts: 2,558 Member
    I'm glad someone wrote this.

    HRMs for weight loss is just marketing for an industry looking to break into a larger market.
  • SingRunTing
    SingRunTing Posts: 2,604 Member
    Just out of curiosity, how do you know your real calorie burn was 1200?

    I'm not questioning your stats, just wanting to learn.
  • The_Enginerd
    The_Enginerd Posts: 3,982 Member
    Just out of curiosity, how do you know your real calorie burn was 1200?

    I'm not questioning your stats, just wanting to learn.
    Experience and data from similar runs in more mild conditions.

    edit to add: Based on long term data on my intake, exercise, and weight, ~120 calories/mile for running is accurate for me.
  • TheWorstHorse
    TheWorstHorse Posts: 185
    Just out of curiosity, how do you know your real calorie burn was 1200?

    I'm not questioning your stats, just wanting to learn.
    Experience and data from similar runs in more mild conditions.

    ^this^

    Another example: The difference between me doing the same steady state cardio exercise at sea level and again at an elevation of six thousand feet is roughly twenty-five percent. And, if I stay at elevation for three or more weeks gradually returns to within five percent of the sea level measure.

    If you keep track of, and analyze, the data you collect, you know when any reading doesn't make sense. If you always accept the data as "true", log it, and never look at it again, it doesn't have much value. And you are unlikely to stay on track for meeting your goals.
  • jrcrmr
    jrcrmr Posts: 31 Member
    I don't completely agree with the aspect that HRMs are just "marketing" gimmicks as I think, as the OP pointed out, it is one of the most reliable tools if you're in a steady cardio activity (jogging/running, steady cycling, etc). The faults are because it's much harder to get your "net" heart rate/calorie burn (meaning, the extra calories you burned from the activity beyond the normal calories burned just from regular activity) on activities that don't bring your heart up. As far as cost goes, like most things, getting something that more accurately describes your personal calorie burn is usually going into the higher range. Much like finding out your personal body fat %, there are lower cost ways (some are even really cheap if you know how to work the instruments) but the best measures, by far, are much more expensive and not usually readily available.


    All that being said, I just want to join a sidepoint made in the OP. I detest people who turn up the heat "to burn more calories." I have a gym in my condo building and there's this one guy who turns off the AC because he wants to burn "twice as many calories" as he said. It's the physical exertion that converts the energy into movement to burn the calories; not the sweat you lose.

    That is all! Good info though..
  • SarcasmIsMyLoveLanguage
    SarcasmIsMyLoveLanguage Posts: 2,668 Member
    Interesting, thanks for the post. I definitely rely on my Garmin HRM but perhaps I should be more careful
  • The_Enginerd
    The_Enginerd Posts: 3,982 Member
    All that being said, I just want to join a sidepoint made in the OP. I detest people who turn up the heat "to burn more calories." I have a gym in my condo building and there's this one guy who turns off the AC because he wants to burn "twice as many calories" as he said. It's the physical exertion that converts the energy into movement to burn the calories; not the sweat you lose.
    Well, it certainly FEELS harder when it's hot! On my normal long runs, I run about 750-800 calories per hour. Yesterday I was under 600 calories/hour, and it felt way harder than my normal runs. Any faster I would overheat.

    For another data point: I ran my typical long run when it was warmer out (80 and in the afternoon sun versus 70-75 and later in day so that finish close to sunset). Same exact run, but my HRM calorie reading was ~10% higher for the warm run versus the cooler runs.
  • The_Enginerd
    The_Enginerd Posts: 3,982 Member
    Bumping this since there are a lot of newbies and I just had another data point to add.

    Today's pace run was done in 86F, 19% humidity, at 10:30 a.m. in full sun. I had a 176 BPM average during the pace portion. On the same workout last week, I had a 164 BPM average despite running 0:22 faster per mile when it was 60F and I ran near dusk.

    Despite being the same workout, my properly set up HRM calculated nearly 200 extra calories, 870 vs 670, for the same workout; 30% more calories.

    Know the limitations and take those HRM calorie counts with a bit of salt. Speaking of salt... I'm sweaty as hell. I'm gonna go down some Cheez-its.
  • Mr_Knight
    Mr_Knight Posts: 9,532 Member
    awarreningermany wrote: »
    I can easily say also that mfp underestimates calories burned...

    99% of the time, MFP is over-estimating burns.
  • marcolbmp
    marcolbmp Posts: 92 Member
    Mr_Knight wrote: »
    awarreningermany wrote: »
    I can easily say also that mfp underestimates calories burned...

    99% of the time, MFP is over-estimating burns.

    You may be right, but I'm hoping you're wrong.
    Do you have any data to back this up?
    I use a HRM and always use a conservative number when I enter it in to MFP, but if I use the MFP estimates, it can sometimes be quite a bit lower. Just curious.
  • Mr_Knight
    Mr_Knight Posts: 9,532 Member
    HRMs also over-estimate, for most people, doing most activities.

    If you want to talk about a specific workout, I'll be happy to work through the math, if you like.
  • kcjchang
    kcjchang Posts: 709 Member
    awarreningermany wrote: »
    I think they are great and rather like mine. I think anything you look at is going to be an estimate and no one is going to know 100% what they burned.

    True and the closest is in a laboratory setting. The problem is not whether it is "over" or "under" estimating but to draw conclusions based zero correlations. It's like predicting the car engine's RPM by reading the gas gauge. It doesn't work, period.

    OP, you been following the power meter development for running? Just saw a post from DC Rainmaker. Should be a major game changer (as in cycling).
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