It sounds about right, I did a century this weekend. Average HR was about 151.33, max of 178. On the bike for 5 hours 42 minutes. Average speed of 18.1, distance of 103.5. I burnt 4,772 calories, and weigh 185. Had my polar on the whole time.

I don't believe it is consistently off; it appears to only use speed, so if you are climbing if will think you aren't doing much. I used to think it took HR into account (because thats what I was told by someone who had one before I got mine), but after looking at the data it seems to underestimate with heavy climbing and overestimate otherwise. Therefore, no consistent factor can be determined.

I've heard (no idea if it's true) that Garmin can't use HR to calculate calories because they don't hold/can't license the necessary patents.

Suck. So if I want to get a better (although still questionable) estimate of calories burned, my only remotely affordable option is to pair my Garmin with a powertap? What's another $1200, eh?

Originally Posted by Booger If Garmin's figures are off, are they consistently off? That is to say, can we extrapolate a multiplier using a more trusted figure? I don't have an SRM, so Garmin is it for me.


i suggest one uses an online cycling calorie calculator for a better estimate. the only way to come up with a solution like yours is to have several people use both computers at the same time for a period of time.

from my reading it appears that Garmin's lack of use of the HR data is the main reason for the inflated numbers. just like UMD posted about.

later.

My numbers come solely from my Polar HRM, which I've relied on in one model or another for 10 years. With height, weight, age, and gender dialed in, the calories burned estimate is based on my body's efforts for that given day, whether I'm climbing, hammering in a club ride, or coaching a class. If I'm looking for a calories burned number, I think it's about as close as I'm going to get for the money.

Am I correct in reading here that you are all primarily using Garmin estimates (not based on heart rate data) for these numbers??

Beth

I was using a Polar HRM. I "calibrated" mine by tracking what I ate very carefully for a while and made an effort to eat exactly what it said I burned + BMR. It was a little high apparently because I gained weight, so I ate less until I reached an equilibrium. It was I think about 10-20% high. When I got the Garmin, I compared the numbers I got to the polar. The numbers were not even close.

Powertaps don't calculate calories burned, they just integrate the work you've done. Garmins are funny. I used to tell my wife I burned 6k calories on rides just for fun. I don't think I've ever put in more than 3 MJ on the bike, even on very hilly 100+ mile rides (I'm lightish though). 500-700 kCal/hr is probably a decent estimate.

18mph on flats is about 170 W or so, which is about 600 kJ/hr, or roughly 600 kCal/hr depending on your efficiency.

I agree that Garmin's numbers may be inflated, but I disagree that it is due to lack of incorporating HR data. At first I thought it might be necessary for the device to use HR data for true calorie burned calculations but now I don't think it matters at all. My reasoning is this: As we exercise more and more, our heart rates should decrease for a given amount of work (to a certain limit). An example, when I first started running and biking my HR would easily be in the 190s to climb a certain hill by my house. Now that I have lost 13 pounds and I'm in better shape, I did the same hill today at my fastest pace yet and my HR was in the 170s.

I didn't know about this thread when I recently posted pretty much the same question in the electronics forum. I too was curious about the accuracy of my Forerunner 305. It always says I'm buring a ton of calories but the fat seems to linger. Thus, I think they can actually be detrimental to training in the sense that one may feel that he can eat more because he burned so many calories when in reality he didn't.

i have both the forerunner and the edge. the edge is way off while the forerunner is slightly off when comparing them to online calorie calculators. like i said, they are all estimates and i suggest using the one that produces the lower estimate if the true goal is weight loss via calorie counting. later.

HR is a poor approximation, but it is better than speed, which is what the Garmin uses. My Polar (RS200) had a test that it used to approximate VO2 performance, which was basically just a determiniation of resting HR and resting HR variability. The lower you could get your HR and the smaller range you could hold it in, the "fitter" it thought you were, and it would update your VO2 max entry with the results. The higher the VO2 max you entered, the less calories it would think you were burning at any given HR, so it did take increased fitness into account. Again, all estimates, but much better than determining calorie burn by speed alone. It basically assumed if you were going really fast you were burning tons of calories, without any regard to the effort. Power is the best measurement, but even there you have to assume an efficiency factor. With HR at least the unit can determine if you are working hard or going easy. With speed it has no idea if you are going 30mph because you have a tailwind, or you are going 5mph because you are trudging up a 15% grade.

FWIW, my highest "score" on the Polar test was 81, when my resting HR was 32. More recently I have "scored" in the low 70s, but I'm much fitter now (I can generate more power at a lower HR), so go figure.

25% efficiency might be high. An article in June08 Bicycling mag refers to physiologist who studies cycling performance at Polar saying most amatuer cyclists are 17-20% efficient, with pros reaching 22-23%.

I'm not totally sold on any device that uses HR for calorie calculations just because there are so many variables that can effect your HR, such as time of day, temperature, recent illness/infection for example. I do think that Polar trick of estimating your VO2 max is interesting and I'll look more into it.

I do totally agree that speed is certainly a useless measurement for anyting other than just that... speed. You're right in that these units think that you are just putzing along only doing 10-12 mph. What it doesn't know is that I'm cranking up an 8% grade and have been doing it for the last 5-6 miles, no wonder I'm so slow. Do they take into account grade at all, anyone know?

Wouldn't altitude throw off a formula base on HR?

I still am not sure of the value of calories anyway. Are people using this for diet, or ride planning?

I am usually starving after a ride, but I just eat til I feel good (not over-full), instead of thinking about the calories.

Exactly. But as an estimation, it's not too bad. And in the spectrum of badness, it's much less bad than Garmin's speed-based algorithm.

My Garmin 305 on my standard 35 mile ride, with about 50ft/mile of climbing and 18+mph calculates 1900-2000 calories. I weigh 160lbs.

listen, not you UMD you get it, the majority think that the Edge ignores HR all together and puts all the importance on speed.

we are saying that the Edge collects enough data to BETTER estimate calories expended then it currently does. it is not one or the other...........it is all the factors.

later.

I do know what you, imparticular, are saying... I do get it. I can't speak about the Edge but I can say that the Forerunner doesn't use HR at all. For me, that's fine because I don't think it needs to use HR in its calculations. And to say that some device has the capabilities to measure different parameters but doesn't do so, doesn't really tell us much. The primary question simply was how accurate are the GPS units at determining calories burned, not what parametes does one unit use to do that.

As for the question as to why one would want to measure such data, for me, it's just a another thing that adds to the joy of cycling. I love riding, I also like losing weight. See the amount of calories burned helps to keep me motivated at losing weight.

To complicate this more, I just did the same check that I did when comparing how the units vs. software applications calculate climbing and grade. It appears that each software application calculates calories differently, based on the data in the unit. In other words, the unit does not transfer a value for calories (I don't think GPX even supports the data type). Instead, the Garmin device, Garmin software, Motionbased, and Ascent, all report different calories for the same ride. I find it really interesting that there is discrepancy in the two Garmin algorithms.

So this begs the question of where are you all reading these values, in the device or in other applications?

I don't really keep a runnig total or anything like that, I just like to look at my Forerunner at the end of a ride and say, "Cool I burned such and such calories." Then treat myself to a Dasani water

So, to answer the question, I just read the number of my Forerunner and call it good there. When I ride on my trainer, that's different story. I have a Kurt Kinetic with the little watt meter that came with it. To know the calories for that I have to actually do a little math. Hey, how many calories can you burn doing math?!

The Edge 205 definitely doesn't use heart rate, because it doesn't collect it.

For those using SportsTracks, there is a Power plugin available that attempts to estimate your power. Now granted, this is an estimate and not as good as a PowerTap or other real power meter. However, the power plugin will also attempt to estimate your calories burned based on the power estimate. Based on the comments in this thread and my experience with a Garmin and SportsTracks, the power plugin is a better estimator of calories burned then Garmin is.