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I have a Garmin Forerunner 301 which shows "Total Calories." That number is much higher than what I calculate just using my weight, time and some speed factors from a book edited by Ed Pavelka, like 50-60% higher. I've wondered about this since I got the unit and finally sent an email to Garmin asking them about it. While not explaining the discrepancy, they did clarify that the unit doesn't use heart rate in the calculation, but there are two new units that do use heart rate in calculating calories burned. Here's the complete response for anyone interested.

"The Forerunner 301 calorie burn data is based on MET values. MET values use weight and how fast an individual moves from point A to point B. Distance plays an indirect roll in this because the further you travel the more time it has to calculate. HR is not used in the calorie calculation. Garmin's new Forerunner 405CX and Forerunner 310XT have heart-rate base calorie computation."
 

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Guy I ride with has a 301. We rode for 1:40 the other night and it said her burned about 2400 calories. There is no way either of us burned that many calories in less than 2 hrs.
More like 1200 or less.
 

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overestimates due to calculations based on Speed. Do a flat 20 mile course with low entisity avg 21 mph and it will say you burned more calories than if you did a hilly ride for an hour and only avg 13 mph. Never liked the idea that it based calculations on speed vs HR, at least thats the case with my 305.
 

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Makes me wonder if it assumes we are running rather than cycling. I could see burning double the calories to run the same distance at the same speed (if that were humanly possible).

I just ignore the calories number.
 

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Useless MET

GerryR said:
I"The Forerunner 301 calorie burn data is based on MET values. MET values use weight and how fast an individual moves from point A to point B. Distance plays an indirect roll in this because the further you travel the more time it has to calculate. HR is not used in the calorie calculation. Garmin's new Forerunner 405CX and Forerunner 310XT have heart-rate base calorie computation."
Bicycling magazine also uses METs for their calorie estimations, and they get equally bogus numers. For a reasonably fit cyclist on a road bike, the MET methodology over-estimates caloric consumption by a vast amount. It is only used by the ignorant or the disengenuous (certainly that applies to Bicycling magazine, whichever you choose).
 
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Calories are just a indirect measurement of watts. If you produce x amount of calories for y amount of time you get z amount of calories burned, no matter what (very similar to the fact that if you run a mile or walk one, you still burn very close to the same amount of calories). Doesn't matter if you're a pro putting out 200 watts and it's a recovery ride for you, or someone who's never ridden before doing the same but killing themselves to do it, they still both burn the same amount of calories. I usually take about .6 of what the garmin says and that gets me to within 3-5% of what I actually burn. It's kinda funny actually, garmin has the formula down, they just always come out high, but consistently high.
 

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Discussion Starter · #8 ·
jains89 said:
I usually take about .6 of what the garmin says and that gets me to within 3-5% of what I actually burn.
How do you know how many calories you actually burn?
 
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GerryR said:
How do you know how many calories you actually burn?
I compare the numbers to an SRM, or my old powertap. A power meter will be with 1-2% accuracy ( or whatever the accuracy of the power meter is) as it's just a conversion formula once you have watts.
 

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When I download the data to Ascent software (I use a Mac) I get a more realistic calorie number. I think Topofusion and other software also do a good job at correcting some of the over generous data from Garmin, Motion based and Training Center. That said, if you use the information to compare your efforts on the same ride to ride, it can be useful.
 

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Simple formula

jains89 said:
I compare the numbers to an SRM, or my old powertap. A power meter will be with 1-2% accuracy ( or whatever the accuracy of the power meter is) as it's just a conversion formula once you have watts.
And yet, in another thread, you use a questionable metabolic efficiency of 18% in your conversion formula, which can be otherwise described as "wrong." Just saying.
 

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No doubt about it, the Garmin is dead wrong. I used to use a Powertap so I basically knew the effort/time/calorie guidelines that I usually do. At first I set my Garmin up with a profile of 110lbs (I'm really 175) but I thought this was still a little overstated so I changed it to 100 lbs and it seems to be pretty accurate.

Of course the Garmin is going to be wrong unless it has power data as calories are just a unit of work done and heart rate is a very bad estimator of work (plus the estimation Garmin uses is exponentially bad).

Dividing your weight by 1.65 to 1.75 seems to do the trick.
 
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