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# Help with big calorie difference in watts formula vs. "usual tables".

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# Help with big calorie difference in watts formula vs. "usual tables".

07-11-16, 11:52 PM
#1
tomcon
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Help with big calorie difference in watts formula vs. "usual tables".

The accepted formula for computing calories burned from watts appears to be:

watts * 3.6 * hrs.

So, for 1 hour at 100 watts, you get 360 calories.

I am a pretty easy-going recreational rider. On a recent ride, almost entirely flat (never more than +/-1% grade), my average Watts (from Power Pod power meter) was 102, and my average speed was 13.1 mph. That calculates to 367 cal/hr.

The trouble is that ALL (as far as i can see) statistics given on the web, and all those "bike calculators", state nearly DOUBLE that figure for calories burned per hour when going 13.1 mph.

Just to name a couple, the calculator at bicycle.com says that, for my wt (174 lbs) I have burned 631 calories for 12-13.9 mph (and my speed is right in the middle of that range). MapMyRide says 780 calories! Other calculators and tables all over the web give a similar but maybe a few percent different figure for calories burned for 1 hour at 13.1 mph. All are way, way, above the 367 cal/hr that the formula gives.

Putting it another way, using the watts -> calories formula in reverse, I would need to be at 175 watts to burn 631 cal/hr. So, we're not talking about a trivial rounding error here.

In fact, typical web tables give values pretty close to 367 cal/hr for walking at 3 mph! (I've seen a range around 310-340).

So, HOW TO RECONCILE THIS?? WHAT IS CORRECT??

Any thoughts/wisdom to offer on this??

Thanks!
07-12-16, 12:01 AM
#2
caloso
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Ignore the web tables. They're useless.
07-12-16, 12:02 AM
#3
Liz33
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I don't know, I don't have the answer. Sorry. Have you tried the application Runtastic? It shows under the name Road Bike. It's the one I use and it counts very little calories burnt, so little that I wonder if it's wrong, but I don't know much about this, so maybe it uses the formula you know.
07-12-16, 01:59 AM
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Machka
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I use the formula ... 100 calories for every 5 km of cycling. That seems to be a reasonable ball-park figure for me.
07-12-16, 06:04 AM
#5
andr0id
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I run a PowerTap and weigh about 190. My numbers are going to be slightly higher than yours, but weight on level ground doesn't change things much.

Assuming road bike, mostly level ground, light wind, out and back or circuit coarse...

Riding 18 -20mph is about 650 Calories/hr. That's around 180 watts or so average.

Riding with my wife at 11-12ish is a lot less, maybe 60 - 80 watts so less than 300 Calories an hour.

Anything that tells you more for less work / riding slower is likely lying.

If I'm riding my fixed gear without power meter, I assume 100 Calories / 10 minutes as an estimate based on equivalent effort and speed.

I would say your power pod is more reasonable that the web sites.

BTW, this is one of the reasons why people don't lose weight cycling. They get back all the calories they've burned in a half hour ride with one bottle of sugary Gatorade. I'd suggest the G2.

Last edited by andr0id; 07-12-16 at 06:10 AM.
07-12-16, 06:19 AM
#6
rm -rf
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Originally Posted by Machka
I use the formula ... 100 calories for every 5 km of cycling. That seems to be a reasonable ball-park figure for me.
Yes. That's the same as 32 calories per mile. The 25 to 30 calories per mile estimate seems to work very well for a lot of riders, and it's verified by those with power meters. This rate applies to "typical" riding, not all-out, max effort rides.

Power Pod
This is from the iBike company, and uses air flow and other readings to estimate power. It's not as accurate as a power meter that measures power at the crank or wheel. But your reading of 100 watts for a 13 mph average sounds correct. (dcrainmaker reviewed, and it's reasonably accurate.)

Calorie estimates
A lot of the GPS based or heart rate calorie estimates are often quite high. I have no idea why they are all like that.

I just googled "calories while walking" and one source had about 100 cal per mile at 3 mph for a 180 pound person. Riding at 13 mph is sort of the same effort as a brisk walk for me, so that sounds about right. Bikes are really efficient!

Last edited by rm -rf; 07-12-16 at 06:30 AM.
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