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  1. #1
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    How accurate is calorie function on HRM?

    Bought a new toy, a Sports Instruments Fit3 HRM, that has a "calories burned" feature based on your weight, max HR, and your HR throughout the ride. During the last ride, it said I burned close to 3,000 calories. Dunno if I should believe this.

    I realize that there is going to be a margin or error. But does anyone know what this margin is? Or whether these toys over- or uner-estimate the actual calories burned?

    I'm curious, because I just found out that I weigh 15 pounds more than last year. I can't affor to buy new pants and I like to eat. So I figure I should just ride more.

  2. #2
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    Quote Originally Posted by No MSG
    Bought a new toy, a Sports Instruments Fit3 HRM, that has a "calories burned" feature based on your weight, max HR, and your HR throughout the ride. During the last ride, it said I burned close to 3,000 calories. Dunno if I should believe this.

    I realize that there is going to be a margin or error. But does anyone know what this margin is? Or whether these toys over- or uner-estimate the actual calories burned?

    I'm curious, because I just found out that I weigh 15 pounds more than last year. I can't affor to buy new pants and I like to eat. So I figure I should just ride more.
    My polar S725 varies +/- 10% compared to my calories on my powertap. Good enough for me. When I do a steady state workout its been as close as 2%, the more coasting you do the less accurate it becomes it seems.

  3. #3
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    Quote Originally Posted by fsrftc
    My polar S725 varies +/- 10% compared to my calories on my powertap. Good enough for me. When I do a steady state workout its been as close as 2%, the more coasting you do the less accurate it becomes it seems.
    So the powertaps are pretty accurate with respect to calories burned?

  4. #4
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    Quote Originally Posted by No MSG
    So the powertaps are pretty accurate with respect to calories burned?
    It is for me, I set up my s725 by doing the VO2 max test they have in it

  5. #5
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    Quote Originally Posted by No MSG
    So the powertaps are pretty accurate with respect to calories burned?
    This has to be the most accurate method, since it calculates calories based on the output to your hub.

    Hub gives you Watts. From finding the area under a Watt/Time curve, you can get kiloJoules. Kilojoules can be directly converted to calories.


    I suspect the HRM companies empirically created a function with a group of test subjects by plotting HR and Calories. So Calories = f(Sex, HR, weight). It's just a curve fit of people using a power tap or equivalent.

    It's just so weird that my wife and I get such different calorie numbers after a ride. I'll have 2800 or so and she'll have 1000. I guess I use three times more energy to do the same ride. I weigh 165 and she weighs 115. This is HRM data.

  6. #6
    ganginwood
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    this has been discussed to no end on rbr.

    the most accurate calculations were determined to come from the free calorie counter on bicycling.com. it gives you about 800 calories per hour working at a good effort. my garmin throws 1200-1300 calories at me for a 1 hour ride. i know thats way off.

    so...according to bicycling mag, 2800 calories would be a 3-4 hour ride pushing lactic threshold.

    here's the link
    http://www.bicycling.com/channel/0,6...tion=_*topnav*

    as far as the polar being +/- 2% accurate, how can we possibly know that? according to their vo2 test?

    i have to admit, when i hear the term kilojoules i think of Back to the Future
    "1.21 jigawatts! 1.21 jigawatts! that's impossible! why, the only thing capable of producing that type of energy is a bolt of lightning. unfortunately we never know where or when it is going to occur......."
    "we do now"
    Quote Originally Posted by Mike Aswell
    the 5th poster, ganginwoods, is correct

  7. #7
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    How is heartrate related to calories burned? It seems like, if you know your heartrate, or perhaps, % of max heartrate, throughout the workout, as well as other key values (e.g., weight) you should be able to get a pretty accurate calories burned calculation. No?

    Also, should calories burned (assuming valid calculation) be a good measure of total workout difficulty across different activities (e.g, running, cycling)?

  8. #8
    Still learning
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    Would use of the Polar Power Output sensor help giving more accurate readings when riding?

  9. #9
    CB2
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    The only thing I use the calorie burned function for is justifying having a piece of cake.

  10. #10
    Gnar
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    I have the Pro 9 from Sports Instruments and it doesn't have a calorie function. They call it "Workload Index".

    The Workload display uses your heart rate and other information to
    calculate a single number which represents the amount of work you
    have performed during a workout. This feature gives you a simple,
    easy to use single number for comparing one workout to another in
    terms of overall effort. When used with Average Heart Rate these
    two numbers give you a quick overview of load and intensity on a
    daily basis

  11. #11
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    Quote Originally Posted by ganginwood
    this has been discussed to no end on rbr.

    the most accurate calculations were determined to come from the free calorie counter on bicycling.com. it gives you about 800 calories per hour working at a good effort. my garmin throws 1200-1300 calories at me for a 1 hour ride. i know thats way off.

    so...according to bicycling mag, 2800 calories would be a 3-4 hour ride pushing lactic threshold.

    here's the link
    http://www.bicycling.com/channel/0,6...tion=_*topnav*

    as far as the polar being +/- 2% accurate, how can we possibly know that? according to their vo2 test?

    i have to admit, when i hear the term kilojoules i think of Back to the Future
    "1.21 jigawatts! 1.21 jigawatts! that's impossible! why, the only thing capable of producing that type of energy is a bolt of lightning. unfortunately we never know where or when it is going to occur......."
    "we do now"
    Wouldn't the most accurate measure be a power meter? just sayin'

    I weigh 185ish and typically do about 900kj/hour with my power tap on normal rides, I've seen almost 1100/hr already for a near time trial effort and a lazy ride is in the 6-700 calorie range. My polar is usually within +/- 5% of that but has been as high as 10% on rides when there is a lot of coasting.

  12. #12
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    Power?

    Quote Originally Posted by fsrftc
    Wouldn't the most accurate measure be a power meter? just sayin'

    I weigh 185ish and typically do about 900kj/hour with my power tap on normal rides, I've seen almost 1100/hr already for a near time trial effort and a lazy ride is in the 6-700 calorie range. My polar is usually within +/- 5% of that but has been as high as 10% on rides when there is a lot of coasting.
    OK, so maybe power is the global metric I'm looking for. What's the formula to calculate it? I've got lots of data to throw into it: distance, ave speed, elevation, heart rate, etc.

  13. #13
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    Quote Originally Posted by swoodbrn
    OK, so maybe power is the global metric I'm looking for. What's the formula to calculate it? I've got lots of data to throw into it: distance, ave speed, elevation, heart rate, etc.
    There is no formula, get a power meter

  14. #14
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    power formula

    Quote Originally Posted by fsrftc
    There is no formula, get a power meter
    Well, there's a formula, but I guess my current rig doesn't give me the inputs (e.g., chain tension, cadence, etc.). Don't need to buy anything else - I'll just ride.

  15. #15
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    Hum, very strange indeed. I would expect a variation between males and females, but nothing almost 3 times different. What HRM are you using and what's your wife using? Is this road rides or trail? I know for sure that I burn more than a lot of people I ride with on the road, because I'm always the one in front blocking the wind/pulling.

    As for hourly calories burnt, my range is somewhere between 500-800 now but when I first got it about 1.5 years ago it was 700-900 or so. guess the fitter you get, the more efficient you get, hence the less power you use/burn. Highest I've done was about 4500 calories on a century ride of about 6.5 hours on road using my MTB w/ knobbies pumped up to 65 PSI.

    Quote Originally Posted by Poncharelli
    ...................It's just so weird that my wife and I get such different calorie numbers after a ride. I'll have 2800 or so and she'll have 1000. I guess I use three times more energy to do the same ride. I weigh 165 and she weighs 115. This is HRM data.
    One day your life will flash before your eyes, will it be worth watching??

  16. #16
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    HRM and Calories

    Your power tap calculates mechanical energy, this is the absolute energy expenditure, however your body is not 100% efficient so therefore you will burn more calories then your powertap suggests depending on how efficient your body is.

    The HRM functions were calculated using a different groups of people of various activity levels. Basically they measured the absolute calorie requirements of these groups of people and graded them into their activity levels (how many hours of activity they do a week). Then they calculated regression formula for each activity level which works out calorie requirements based on HR readings. This is why the polar monitors require that you select your activity level and age etc, if you put these in differently you will get different calorie readings, and different test results (VO2 max etc.).

    I have personally used mine (Polar S610) in the lab where I was measuring my real energy expenditure by my expired air. My HRM was almost bang on with the real readings we were taking with air expenditure. I would personally vouch for the polar system if you set it up correctly.

    Regards,
    Dave.

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