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  1. #1
    He drop me Grasschopper's Avatar
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    Calorie burn differences from one Garmin to the next and one program to the next

    Ok so I'm a bit confused here. I run a Garmin Edge 705 with HR monitor and use Training center as well as Runkeeper.com to track my riding. I know from all of the discussions since the Edge line came out (I had a 305 before the 705) that the caloric burn number they give out is WAY over inflated but let's look at my ride with my wife (she is just getting into cycling and still building up the muscles so a bit slower than I would ride solo) yesterday in Training Center: Distance 32.97 mi, ride time 2:26, avg speed 13.5 mph, 2276 cal burned, 130 bpm avg HR, 1557' ascent

    Now compare those numbers to Runkeeper.com which links with the Garmin and downloads the same data file: Distance 32.85 mi, ride time 2:26, avg speed 13.42, 1584 cal burned, 127 bpm avg HR, 1458' ascent. Same ride mind you...more miles by just a tad, lower avg HR by a couple of beats per min. Obviously the biggy is the difference in calorie burn at nearly 700 cal different. I would assume the Runkeeper number is much more realistic.

    Now factor in my wife's numbers...she uses a Garmin Edge 500 and comes up with similar number for the ride in terms of distance (makes sense) but for calories she gets an even lower number even on Training center...her number was like 1200 calories but her average HR was higher (we are also a similar weight) because she is farther out of shape than I am. I would think that she would have burned more calories...and apparently Garmin changed something on the device level when calculating caloric burn.

    Any thoughts here?
    Last edited by Grasschopper; 06-11-11 at 10:23 AM.
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  2. #2
    Senior Member ericm979's Avatar
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    Those are all guesses. They're different because they use different algorithms. There is no direct correlation between HR and calorie consumption. People's HR varies for the same power output (calorie consumption). Two riders who are in the same shape, weight and age, producing the same power, may have HRs that are 20 bpm different.

    The only ways to measure instead of guess calorie consumption is to measure power output, or to measure something that indicates metabolism, such as oxygen (air) consumption or CO2 exhalation (and then subtract basal metabolism). The latter is what's used in lab studies but you can't take that equipment out on the road, and you wouldn't want to breathe through a mask for 2.5 hours if you could. You can measure power with a power meter, and then make a guess about riding efficiency in order to estimate calories. Efficiency ranges from about 17-23%. Most people assume the higher end because then the conversion from kJ to calories works out so that the number of kJ equals the number of calories. Unless you're at the high end of efficiency this number wind up being slightly low.

    I would ignore the calorie guesses entirely, or use the lowest one you can find and realize that it's not accurate and is probably still too high. 1580 cal for a 2:26 ride at 13 mph with not much climbing sounds low, unless perhaps you're over 200 lbs.

  3. #3
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    Agree with Eric above.

    The edge 500 is supposed to be more accurate than earlier Garmins. It's quite likely your wife burned significantly fewer calories than you if she is lighter and/or spent more time drafting you. For reference, based on the runkeeper.com estimate, you would have been averaging about 175 watts for 2 1/2 hrs and your wife's Garmin would have indicated an average power of around 133W. For the 705 to be correct you would have had to have averaged over 250W which is basically not possible at 13MPH so the Edge 500 and the running site are probably in the right ballpark but the 705 isn't close.

    Regarding your wife burning more calories because she is out of shape, it doesn't really work that way. Your efficiency is basically fixed and difficult to change. As your fitness improves your speed/power will go up and you will be capable of burning more calories/hr.

  4. #4
    He drop me Grasschopper's Avatar
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    Well great thanks for all of the information...I've learned a few things. I will say I did know they are all guesses, I was hoping to try to figure out which is the best guess.

    So I am over 200 lbs, 216.8 as of this morning.

    Is there a calorie estimator that is generally considered more accurate than others? I'm thinking it ISN'T caloriesperhour.com because that site says the burn for this ride would have been around 2041.
    Last edited by Grasschopper; 06-11-11 at 10:31 AM.
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  5. #5
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    These things use an equation to estimate your calorie burn. In order to do it right, it would have to know your weight, the weight of your bike, the width of your tires, you tire inflation, the wind speed and direction, you speed, distance travel and grades climbed. It would have to factor all that stuff in together and it would still be an estimate.

    The best way I know of estimating calories burned is to measure C02 production during respiration. Even that is not a direct measure because burning fats, carbohydrates and proteins all give different values of Calorie burn vs C02 production. By the way, measuring C02 production is not really practical outside of a laboratory.

    Measuring power out put is another way but that is not as direct a measure as C02 production.

  6. #6
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    I have a Garmin 705 and just got a powermeter. The Garmin overestimates my calorie consumption (compared to KJ on the PM) by DOUBLE!

    My friend has a Garmin 500, her's is a lot closer, but still overestimates.
    ...

  7. #7
    NeoRetroGrouch
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    Bottom line - a good, calibrated power meter is plus/minus 10-20%. All others are useless. - TF

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