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Calorie Confusion

Old 08-04-14, 09:24 AM
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Calorie Confusion

I've learned long ago not to trust the calorie burn estimator's out there.



If I multiplied the distance and the reported calories by 10 I get 53.4 miles and 3,800 calories. I did a ~53 mile ride this weekend at a similar effort and Garmin reports 1/2 the calories.




Same: Bike,Rider info, Device, HRM.
Am I missing something or is this just an absurd inconsistency?

What brought this to my attention is I recently synced my Garmin connect account with MyFitnessPal.
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Old 08-04-14, 09:59 AM
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Originally Posted by bbeasley
I've learned long ago not to trust the calorie burn estimator's out there.
They use a really poor algorithm. 1661 is probably a reasonable number, the algorithm they license to use while an HRM is active isn't too bad. If you assume that number includes basal calories it probably isn't too high. ~30 calories per mile is reasonable if you're riding solo and you're in good shape. That number might still be high if you were drafting a lot or had a big tailwind and your cardio isn't as good as the software assumes.

If you don't have a HRM active Garmin's algorithm is as bad as anyone's.

The only way to really get a close estimate is to use a power meter and know exactly how efficient you are.
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Old 08-04-14, 10:20 AM
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The Garmin seems a little more realistic as to what you burned.
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Old 08-04-14, 10:21 AM
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Originally Posted by kc0bbq
They use a really poor algorithm. 1661 is probably a reasonable number, the algorithm they license to use while an HRM is active isn't too bad. If you assume that number includes basal calories it probably isn't too high. ~30 calories per mile is reasonable if you're riding solo and you're in good shape. That number might still be high if you were drafting a lot or had a big tailwind and your cardio isn't as good as the software assumes.

If you don't have a HRM active Garmin's algorithm is as bad as anyone's.

The only way to really get a close estimate is to use a power meter and know exactly how efficient you are.
Wouldn't the HRM account for drafing/tailwind as the effort and HR would be less?
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Old 08-04-14, 10:25 AM
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That's why I try not to eat the calories I exercise.
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Old 08-04-14, 10:41 AM
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Originally Posted by bbeasley
I recently synced my Garmin connect account with MyFitnessPal.
I'd venture a guess that 3,800 calories is way off. At that avg speed on my flat (yes, my flat is different than your flat) training ride my kJ burn is ~800/hr and Garmin reports the calories as 540/hr

The fact that you got Garmin and Strava (kJ energy output) to report similar numbers is amazing.

I *used* to use Training Peaks and just add my meals/food and when I uploaded a run or ride to Training Peaks all the math was done for me using the powermeter kJ calculation. Now that Training Peaks is no longer allowing me to add foods I have to join My Fitness Pal and then somehow sync the two.
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Old 08-04-14, 10:49 AM
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I pretty much totally ignore the calorie burn calculations, I let Wahoo post the workout to Myfitnesspal but I only rarely eat back any of the exercise calories......and even then it is only typically 25 or so to let me add one minor food item.

If I am planning a big ride, big for me being say a metric century I will eat 300 back the day before, and 300 the day of the ride, but that has only been once so far :-). I am on a 7000-10,000 calorie a week deficit at present, will be til April next year if it all goes according to plan :-).

The "Calculator" ap was about the most conservative I have found calorie wise for a given ride time and average speed.

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Old 08-04-14, 11:20 AM
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Originally Posted by bbeasley
Wouldn't the HRM account for drafing/tailwind as the effort and HR would be less?
For as accurate as it normally is I would assume the algorithm makes some assumptions about your fitness level based on the speed. I might be way off base, though. It requires a lot more joules to move a bike forward than to power the heart and lungs. The model would break if your heart is working harder than what it thinks your legs are doing. For example, say you're barely hanging on inside a big group because your cardio is not up to it, but you're essentially totally out of the wind. (This example isn't you, just a worst case).

It's not going to me much different, because that is showing not much more than 30 calories per mile. I don't imagine it's more than ten percent, where the really bad 75 calorie per mile estimate is 150% higher than even that.

I imagine it could be wrong in the other direction in some circumstances, too...
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Old 08-04-14, 12:50 PM
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Hmmmm, makes sense. On the longer ride I was having a really good day. By that I mean low HR and no trouble maintaining pace. So this should equal less calories. On the short ride, I do something a bit sketchy. No warm up, just ride hard from driveway to driveway. This really get's my heart jacked up in a hurry and I have to push hard to keep the average up as it's such a short ride. At the two stop signs, I actually have to slow way down or stop as they're a bit dangerous causing my average to plummet. All this drama should equate to more calories.

I think I've just come up with an excuse to buy a power meter
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Old 08-04-14, 01:29 PM
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Originally Posted by bbeasley
Hmmmm, makes sense. On the longer ride I was having a really good day. By that I mean low HR and no trouble maintaining pace. So this should equal less calories. On the short ride, I do something a bit sketchy. No warm up, just ride hard from driveway to driveway. This really get's my heart jacked up in a hurry and I have to push hard to keep the average up as it's such a short ride. At the two stop signs, I actually have to slow way down or stop as they're a bit dangerous causing my average to plummet. All this drama should equate to more calories.

I think I've just come up with an excuse to buy a power meter
all I can tell you is prepare to be humbled regarding how much you think your doing effort wise, and how many watts that actually equals. I also found HR has almost no bearing on watts over time. I have had rides where my average HR was 10-15 higher with same watts average....cant explain why.

I dont buy you can train on perceived effort or HR.

Just consider the fact that as you get more fit, you can maintain the same average watts with LESS HR.

Now back to lurkdom..
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Old 08-04-14, 01:47 PM
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Originally Posted by vesteroid
all I can tell you is prepare to be humbled regarding how much you think your doing effort wise, and how many watts that actually equals. I also found HR has almost no bearing on watts over time. I have had rides where my average HR was 10-15 higher with same watts average....cant explain why.

I dont buy you can train on perceived effort or HR.

Just consider the fact that as you get more fit, you can maintain the same average watts with LESS HR.

Now back to lurkdom..
Yeah, I've got no delusions of grandeur when it comes to power. I borrowed one once and it read "You Suck"

I am, however, easily motivated by screens. When riding alone, I put my Garmin on a screen that only displays cadence, average speed, and current speed. I always ride harder when watching this. When I feel well, if my average speed drops below 18 MPH I try to move it up. Data Geek? Type A personality, who knows but it works.
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Old 08-04-14, 01:54 PM
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Originally Posted by vesteroid
all I can tell you is prepare to be humbled regarding how much you think your doing effort wise, and how many watts that actually equals. I also found HR has almost no bearing on watts over time. I have had rides where my average HR was 10-15 higher with same watts average....cant explain why.
Because you may be fatigued, or overheated, or just not quite "at it". The body isn't a machine, it's a biological system, and it doesn't always perform with 100% consistency.

I dont buy you can train on perceived effort or HR.
Yes, you can. A powermeter certainly adds another dimension, and makes it possible to be reasonably precise about outputs, but using HR intelligently will certainly allow you to make a training plan and get fit. It's less precise than power, but it is telling you different things.

Just consider the fact that as you get more fit, you can maintain the same average watts with LESS HR.
Of course. But if you train properly with HR, you'll retest your LTHR every month or two and reset your zones accordingly. So you'll be increasing your training load while staying in the same zones, just as you do when revising your FTP upwards after a retest. You won't know how many watts you're putting out for a given level of effort, but the object of the exercise isn't to count watts, it's to get faster.

Don't get me wrong, I have no doubt of the benefits of training with power. But using power and HR together, as separate data points, is superior. And using power on its own, without regard to HR or perceived exertion, can be problematic for precisely the reason you mention - some days one simply can't hit the numbers, and it may be a good idea to look at HR, listen to one's body, and back off.
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Old 08-04-14, 02:23 PM
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Originally Posted by chasm54
...just as you do when revising your FTP upwards after a retest.
Through an incentive from our health benefits at work, I hope to pick up an HR monitor so I am reading threads on HR when I see them. I finally have to ask as I have seen this acronym many times, what is FTP? All I can find with google is "File Transfer Protocol".
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Old 08-04-14, 02:45 PM
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Functional Threshold Power.

My understanding is this is how hard you can go before your body needs to dip into Glycogen stores to maintain the current level of effort. At this point you're starting to go anaerobic and it will be a short trip.
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Old 08-04-14, 04:07 PM
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you measure FTP (one method) by doing a 20 minute all our effort. the goal is to fall off the bike at the end of 20 minutes totally spent with nothing left. You then take your average watts for that period and multiply *.95 Thats your FTP. This theoretically represents the maximum power output you can ride for an hour.

I have to admit I dont keep up like I use to on all these details and smart fast people like IBO may want to chime in, but this is close enough for most on this board
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Old 08-04-14, 04:19 PM
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Originally Posted by vesteroid
you measure FTP (one method) by doing a 20 minute all our effort. the goal is to fall off the bike at the end of 20 minutes totally spent with nothing left. You then take your average watts for that period and multiply *.95 Thats your FTP. This theoretically represents the maximum power output you can ride for an hour.

I have to admit I dont keep up like I use to on all these details and smart fast people like IBO may want to chime in, but this is close enough for most on this board
Close enough for pretty much everyone. Except IBO, of course. He multiplies his by 1.05 instead of .95, so he can be absolutely certain that he'll throw up after every training session.
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Old 08-04-14, 04:30 PM
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Originally Posted by bbeasley
Functional Threshold Power.

My understanding is this is how hard you can go before your body needs to dip into Glycogen stores to maintain the current level of effort. At this point you're starting to go anaerobic and it will be a short trip.
Er, no, not exactly. At threshold you're already fuelling your effort mainly from glycogen rather than fat.
here's an explanation.

But once you're anaerobic you're using just glycogen stored in the muscles, and the build-up of lactate products is more rapid than you can metabolise them. They used to call it "oxygen debt".

Last edited by chasm54; 08-04-14 at 04:40 PM.
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Old 08-06-14, 01:19 PM
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Originally Posted by vesteroid
you measure FTP (one method) by doing a 20 minute all our effort. the goal is to fall off the bike at the end of 20 minutes totally spent with nothing left. You then take your average watts for that period and multiply *.95 Thats your FTP. This theoretically represents the maximum power output you can ride for an hour.

I have to admit I dont keep up like I use to on all these details and smart fast people like IBO may want to chime in, but this is close enough for most on this board
I can't be smart nor fast. Spent the best 8 years of my life in High Skool and get dropped regularly. Strike 2.
I use the 30 min effort with the last 20 multiplied by .95 OR my last 40K TT effort to arrive at my pFTP number.


Originally Posted by chasm54
Close enough for pretty much everyone. Except IBO, of course. He multiplies his by 1.05 instead of .95, so he can be absolutely certain that he'll throw up after every training session.
Nope. I use the .95 deal (or 40K power) and I've only thrown up in one trainer (FTP measurement) session and after 4 of the 7 TT's I've done. The last one on the 40K was #awesome and #Epic . Lady for sure wanted to call the ambulance.
Haven't managed to go hard enough while training to enjoy that particular aspect of a training session. Hard fer me to physiologically go there.
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