Question about HRM and BMR - double counting?

GenF32
GenF32 Posts: 184 Member
in Fitness and Exercise
Hi there, I have a question I'm hoping someone can answer for me. I have a new HRM that arrived yesterday, and I'm wearing it today at work to try and get a sense of my daily burn on a fairly sedentary non-exercise day. My question is, I know that my BMR is approx 1450, and I know that BMR basically means the calories that are required to keep all your organs functioning in a coma, presumably including your heart.

So, if I measure my burn using my HRM, that obviously uses my heart rate to estimate the calories burned, is it a simple case of adding this daily reading to my BMR to get a (very rough) estimate of total burn (obviously excluding the extra calories burnt digesting food - I know there is a separate formula for this), or am I running the risk of double-counting calories? Obviously some of the BMR calories are related to heart beat, hence my confusion.

I hope someone out there has some insight into this. Trying to google something like this is challenging and I do (allegedly) have a day job ;-)

Cheers in advance.
Gen

Replies

  • danekin
    danekin Posts: 21
    The quick answer is yes, it is double counting, but the value really is trivial. What you could do to make it more close to accurate is divide your BMR by 1440 (24hours x 60minutes) which produces your BMR per minute. Then subtract your workout time times BMR per minute from your total burn calculated on the HRM.

    So, for your BMR you're basically burning 1 calorie per minute, so for a 45 minute workout just subtract 45 calories from your HRM calorie burn.
  • GenF32
    GenF32 Posts: 184 Member
    Oh cool, thanks Dan! Maybe I should have just come straight to you first rather than post here :-)

    And when I'm not actively 'working out' but still obviously moving around and not in a coma, should I still subtract the 1 calorie per minute? You're right that that's actually a miniscule amount - presumably that 1 calorie per minute (don't know why I hadn't thought to divide the BMR by minutes in the day) is in fact divided up between all the main bodily functions, not just keeping my heart pumping.

    I've burnt 600 calories since 8am today, which is approx 348 minutes, so approx 250 over BMR.

    No real reason why i need to know this - just being a nerd as usual.
  • danekin
    danekin Posts: 21
    Your BMR is resting burn, which is your heart, lungs, brain, and other organs consuming energy. The other thing to factor in for more confusion is your HRM calculates energy burn based on cardiovascular activity. This means that your caloric burn for activities such as strength training will be different, so I am guessing that technically offsetting it for BMR would be flawed because it is only grabbing the heart beat as a means to calculate energy burn and in that makes a number of assumptions that in some cases could corrupt the accuracy of the burn calculation.

    If you are using the MFP settings you have to remember that it works on TDEE, which is your BMR + Lifestyle (base rate) which is a pretty good estimate. In any case you would be safe to just count your calories from your HRM as is for your workouts.

    Science!!
  • danekin
    danekin Posts: 21
    For your nerdy curiosity, this is how HRMs work.

    Male Calories Burned = (0.2017 x age in years + 0.09036 x weight in pounds + 0.6309 x average heart rate - 55.0969) x time elapsed / 4.184

    Female Calories Burned = (0.074 x age in years - 0.05741 x weight in pounds + 0.4472 x average heart rate - 20.4022) x time elapsed / 4.184
  • GenF32
    GenF32 Posts: 184 Member
    Ok wow, that's taking nerdy to a whole new level :) But thanks!
  • GenF32
    GenF32 Posts: 184 Member


    In any case you would be safe to just count your calories from your HRM as is for your workouts.


    Yes I was thinking that given most of my workouts are PT sessions with a mix of strength training and short bursts of cardio, the burn according to my HRM doesn't obviously include the ongoing burn from my muscles recovering (and most of the time I'm only just stopping being sore from one session when the next session time rolls around) so if anything it's an underestimation of the total burn I'm getting from those workouts.

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