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  1. #1
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    Accurate HRM calorie count - Edge 705 or Polar F6?

    I had been using my Polar F6 for a couple years now and had always assumed it gave an accurate estimate of calories burned. I just picked up a Garmin Edge 705 with HRM and Cadence bundle. I noticed that it seemed my calories total seemed higher than usual, so today I did a test.

    I put on both the Garmin strap and the Polar strap and went for a 2 1/2 hour ride. Any time I looked at the readings, I saw similar numbers for current heart rate, always within a beat or two. Avg heart rate for the ride on the Garmin was 143bpm, Polar 144bpm; both recorded max rate of 168bpm. But my Polar calculates calories burned at 1646, while my Garmin at 2509!

    So I'm wondering which one is likely more accurate. I double checked that both were programmed with my correct weight, and they were.

    If it was only 100 or 2 calories different, I wouldn't care. But now, do I need to eat an extra meal? 900 calories is quite a difference!

    (I tried to search if anyone has discussed this topic before, but didn't come up with anything.)
    A ride a day keeps the therapist away.

  2. #2
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    Quote Originally Posted by Jwiffle
    If it was only 100 or 2 calories different, I wouldn't care. But now, do I need to eat an extra meal? 900 calories is quite a difference!
    I would say you are eating enough if a 900 kcal difference has not eaten away at you over the last few years.

    That is - if you start adding extra meals now, won't you just put on weight?

  3. #3
    GeoMan
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    Well, you have to understand, calorie counts are a bit "unscientific". For instance, how does your Edge or Polar account for wind conditions (which we all know affects how hard we peddle), temperature conditions (you'll burn more calories if you are hot or cold), or your own personal body metabolism?

    Each company uses an algorithm to calculate calories using the information collected and available to each unit. For instance, does your Polar measure elevation gain and loss? Climb?

    That being said, calories counts will often be debated. Use the number as a general guideline as there are too many variables to consider for any fitness computer to be completely accurate except in a lab setting.

    If you're worried about your weight, I'd use a scale. LOL!

    Anyway, I hope this helps.

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  4. #4
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    Geoman-

    Do you know if any HRM's are sophisticated enough to allow programming an individuals' Resting Metabolic Rate (RMR) into their equation? RMR is an individuals, tested, resting calorie burn rate at rest tested first thing in the morning before exercise, meals, caffeine, etc.

  5. #5
    GeoMan
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    Quote Originally Posted by spec306
    Geoman-

    Do you know if any HRM's are sophisticated enough to allow programming an individuals' Resting Metabolic Rate (RMR) into their equation? RMR is an individuals, tested, resting calorie burn rate at rest tested first thing in the morning before exercise, meals, caffeine, etc.
    I have yet to see one but that sounds pretty cool! I'll keep my eyes peeled.
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  6. #6
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    Yeah, I guess I'll be able to use either as a guide for training purposes. I wonder if the Garmin isn't more accurate for me, though, as I tend to always be hungry and eat a ton. I may have been thinking, "but I only burned 1600" when I actually burned quite a bit more.

    And as far as weight goes, I'm not worried about gaining weight. I only weigh 155 at 6'1", and it's a struggle to add weight.

    Mainly I'm just curious why the disparity and if there was a way to know which was more accurate. I wonder if the Garmin factors in the elevation, etc as Geoman wrote about. I know the F6 is marketed as an indoor trainer HRM, and so might not include some variables the Garmin does.

    I guess it doesn't really matter, as the heart rate itself is more important for training purposes than calories burned.
    A ride a day keeps the therapist away.

  7. #7
    3D guy
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    This is from the top of my head so it might be exact but it is close. They calculate calories very differently. I understand Polar has a patent on HR only Calorie calculations (also using age, weight, gender, likely max HR and I think resting HR). See for example (study funded by Polar):

    Prediction of energy expenditure from heart rate monitoring during submaximal exercise.

    Garmin has to obviously use their own method. Originally it was non-HR dependent and I found it was all over the place. They have since tuned it to use HR (AFAIK) and it seems to consistently given reasonable energy expenditure for amount of time and effort for me (assuming I accept one reading as accurate the others seem to be in line for different lengths and exertion levels).

    So, each is different but in the end you likely want a measure of exertion over time which can be compared workout to workout and think either give you that, not sure which is more accurate for you though in terms of actual kCals.
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  8. #8
    GeoMan
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    Quote Originally Posted by GEOMAN
    That being said, calories counts will often be debated. Use the number as a general guideline as there are too many variables to consider for any fitness computer to be completely accurate except in a lab setting.
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  9. #9
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    Thanks for the info, guys.

    So it looks like I need a computer that calculates based upon the RMR, a powertap, HR, blood pressure, cadence, outside temperature, elevation/grade, VO2, barometric index, and maybe a couple other variables--number hours of sleep last night, etc, and I could get something close to accurate.
    A ride a day keeps the therapist away.

  10. #10
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    I know that my Polar F11 watch is less accurate than using the Polar chest strap with my treadmill because the treadmill also calculates incline for calories burned, while the F11 watch does not use this in the calculation. I would think anything that uses more input calculations should be more accurate than a source with less inputs for the calculation.

  11. #11
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    Quote Originally Posted by Jwiffle
    Thanks for the info, guys.

    So it looks like I need a computer that calculates based upon the RMR, a powertap, HR, blood pressure, cadence, outside temperature, elevation/grade, VO2, barometric index, and maybe a couple other variables--number hours of sleep last night, etc, and I could get something close to accurate.
    And a trailer to pull it, oh, and a physician to calibrate it all. Tandem with a BOB trailer and you are there.....
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  12. #12
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  13. #13
    Let's ride SuperModerator
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    The Garmin is near useless for Calorie count. All the seem to take into account is mph. On a long roadbike ride, you'll burn thousands. On a long MTB ride, you'll burn 1/3 of that. On a hard trainer ride where it only has HR info, and NOT mph info, you burn almost nothing. I've tested these on my polar 720 and my 305. The Garmin is great for many things, but kcal isn't one of them. I hope they fix it at some point.

  14. #14
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    Quote Originally Posted by rensho
    The Garmin is near useless for Calorie count. All the seem to take into account is mph. On a long roadbike ride, you'll burn thousands. On a long MTB ride, you'll burn 1/3 of that. On a hard trainer ride where it only has HR info, and NOT mph info, you burn almost nothing. I've tested these on my polar 720 and my 305. The Garmin is great for many things, but kcal isn't one of them. I hope they fix it at some point.
    Apparently you are correct. I just did a big ride yesterday (Shenandaoh 100!), but didn't wear the HRM strap. When I was looking at it after the ride, turns out it says I burned about 8000 calories. So I guess HR isn't even part of the equation, as I had not expected to see any numbers for calories burned. Although 8000 probably wasn't too inaccurate considering it was a 12.5 hour ride. I wonder if it adds HR to the equation when you are wearing the strap and if it would have changed the numbers any.

    I may do an experiment on my regular road loop, see what kind of calories it records when I don't wear the strap and when I do (if I can manage to keep my effort about equal).
    A ride a day keeps the therapist away.

  15. #15
    GeoMan
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    Please let us know the outcome of your experiment. I, for one, am very curious.

    Like other components of the Edge system, the Edge compensates for missing pieces of the pie. For instance, without the cadence/speed sensor it relies entirely on the GPS for speed and distance. It might be the same with the heart monitor and calories but I have not found documentation validating this.

    Thank you!
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  16. #16
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    Well, I determined that the Edge 705 does not take HR into account at all when calculating calories. I did a very simple experiment. I turned it on and let it sit on my desk for 30 minutes. 0 calories, to be expected. I reset it and let it sit while I wore the heart rate strap for 30 minutes. 0 calories. I put on the Polar and while just sitting and typing at the desk, I burned 12 calories in 10 minutes.

    Anyway, I guess that settles our curiosity. In which case although, like we've said earlier, the Garmin can be used for comparing similar workouts off its readings, I don't think it's very accurate. If it's only determining calories burned from speed, it's going to be an incorrect measure, as it would read more calories burned coasting downhill than grinding uphill! I'd have to do an experiment to determine if it calculates the elevation gain/grade into the equation. So I imagine the Polar is probably closer to determine actual calories burned (even if it doesn't matter).
    A ride a day keeps the therapist away.

  17. #17
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    Well

    I know the garmin uses more then speed and distance. At the very least it is using time and elevation. I do a ride at least once a week and use it for a time trial sometimes. I takes me a little over an hour to get to the top of the climb and its about 800 calories when I am just riding, and close to 1000 when I am pushing hard. Also I never wear the heart rate strap so it is guessing at how hard I am working and can tell when you are going harder. Also it only adds like 200 calories for the 30 min trip down even though I am going much faster. So its definatly using elevation gain/loss, and time.
    I also feel like the edge guesses high, so I tell mine I weigh less then I do.

  18. #18
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    I have compared my entry level Polar CS100 with my Garmin 305. The stats were taken over 88 hours of riding with the Garmin and 50 hours with the Polar. I am 42 years, 77kg. The average heart rate with both these machines for various training rides was 133-138(72-75% of max). The Polar gave a value of 0.071 cal/heart beat. The Garmin indicated 0.09 cal/heart beat. Both were used with HRM's. If the Garmin was used without the HRM, it gave an even higher value.(5500cal vs. the 3200cal "calculated" by the Polar.)
    My conclusion? A highly optimistic calculation to make you feel good about your training. The Garmin might be the most optimistic.
    PS: At a resting HR of 50 my cal consumption/ heart beat should be around 0.029. Calculation! not a true measurement.

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