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Discussion Starter · #1 · (Edited)
I've got a question that nobody seems to know the answer to:

How efficient is my body at using Calories?

If my heart rate monitor (Polar F11) says I burned, 1000 Calories, does that mean my body did 1000 Calories worth of work, or that I did enough work to necessitate eating 1000 Calories.

If the body was 100% efficient, it wouldn't matter, but if it is only 50% efficient at using the energy it consumes (above BMR), then to do 500 Calories of work, I would have to eat 1000 Calories of food.

I am very curious to know, because I am putting together a report on how far it is possible to travel on the amount of energy in a gallon of gasoline (31,000 Calories). You can read about the adventure at http://onegallon.blogspot.com

*** UPDATE ***
The ride is now in the archives, check http://onegallon.blogspot.com/2006_06_01_onegallon_archive.html

for the actual ride.

Thanks!
 

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There's missing data here. The real question is ... If a biker leaves New York burning 1000 calories an hour, and another leaves LA burning 800 calories an hour...who's riding Campy and where will they run into each other? The second question is, did shaving the legs help the guy who only used 800 calories. :)
 

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The latter. The Polar is estimating total Kcal-- BMR + work + wasted energy. Since it only knows your body weight, speed, and elevation gain, it isn't very accurate. You could be doing 12 mph on the flat because you are loafing, or because there is a 30 mph headwind. The Polar would say the same for both, but you'd be working much harder on the latter ride.
 

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ericm979 said:
The latter. The Polar is estimating total Kcal-- BMR + work + wasted energy. Since it only knows your body weight, speed, and elevation gain, it isn't very accurate. You could be doing 12 mph on the flat because you are loafing, or because there is a 30 mph headwind. The Polar would say the same for both, but you'd be working much harder on the latter ride.
It uses your heart rate which would not be the same for those two rides. Also, I don't think it knows anything about altitude. Think it includes BMR? I shouldn't, but it could.

Though I disagree on how it does it, I do agree that it is just an estimate. Numbers I've seen have seemed to be way high.

TF
 

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Two answers

nick2ny said:
I've got a question that nobody seems to know the answer to:

How efficient is my body at using Calories?

If my heart rate monitor (Polar F11) says I burned, 1000 Calories, does that mean my body did 1000 Calories worth of work, or that I did enough work to necessitate eating 1000 Calories.
First, your HRM is probably reading 40% high, based on the numbers I see reported here often. You burn about 600 calories in an hour of riding on the flats at 20 mph, no wind. 1000 calories would be about 250 watts, and that would give you a bit over 24 mph.

Second, it is estimating your total calorie burn - your body is probably about 24% efficient. Couch potatoes are around 18% efficient, and I hear that the highest numbers recorded are just shy of 30% efficient. So 1000 calories burned means about 240 calories delivered to the pedals, which is about 250 watts.
 

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Get thee to a sports lab

nick2ny said:
I've got a question that nobody seems to know the answer to:

How efficient is my body at using Calories?!
I thought I answered this an another thread?

nick2ny said:
If my heart rate monitor (Polar F11) says I burned, 1000 Calories, does that mean my body did 1000 Calories worth of work, or that I did enough work to necessitate eating 1000 Calories.!
The Polar heart rate monitor can say what ever it wants, but at best it can only give an educated guess. While there is a relationship between heartrate and calories burned, unfortunately there are more variables than that, and besides, the relationship is a very individual one - one persion might be buring 1000 calories an hour at 150 beats per minute, and another person could be burning only 500 calories an hour (depending on many things, like rider size, lean muscle mass, max. heartrate, resting heart rate, etc., etc.). There is also the phenomon on heartrate drift - under a high work load, heartrate at a given power output tends to increase over time.

As far as how much of the calories burned gets converted into useful energy, that also varies between individuals. As Kerry stated, the spread can be quite large - one rider might be generating 50% more work per calorie burned than the next rider.

The only way to be sure how your heartrate relates to calories burned and how your calories burned relates to work output is to go to a sports lab and have yourself measured. The most likely test for this would put you on a calibrated ergometer (basically a stationary bike with a powermeter) to measure power output, while wearing a heartrate monitor to measure heartrate, and while wearing a breathing mask attached to O2 and CO2 monitors (to measure calories burned). Only then would you be able to relate heartrate to calories burned and work output.
 

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I compared my heart rate monitor to my power tap for an hour workout. The powertap said that I burn 800 calories where my heart monitor said I burned 640. My weight in the heart is what I weight before the workout. I change this everytime.
 

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nick2ny said:
How efficient is my body at using Calories?

Agree with Mark, Kerry. Labs will tell the truth, but you can say probably better than 20%, worse than 30%.
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If my heart rate monitor (Polar F11) says I burned, 1000 Calories, does that mean my body did 1000 Calories worth of work, or that I did enough work to necessitate eating 1000 Calories.
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IT THINKS the latter, but like others have said every HRM calculator in the world, as well as every "excercise calculator" website, posts 25-50% high on cycling. I wish I knew why -- maybe they don't calculate the effeciency of a roadie's cadence and aerodynamics? 1 hour @ 20 mph flat ~ 550 kcal.

Of course, my interval ride yesterday, using my lab-snagged results for calorie burning plus an HRM, burned like 2,600 calories. I made pretty much an entire bag of pasta. Mmm. Pasta. Garlic. Pinenuts. Bread. More garlic.

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On ONEGALLON.BLOGSPOT.COM -- I've had similar thoughts myself seeing gas at $3.25 / gallon. That's sort of ridiculous. Of course, how much 31,000 kCal of food would cost, I'm not sure ...
 

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Discussion Starter · #9 ·
Argentius, that's a great point about food! You get to choose how much it costs! With gas, you have three choices, $3.09, $3.19, and $3.29 With food, you can run on caviar and champaigne, and it will cost a pretty penny for each calorie, or you can grow the food in your back yard and bike around for free (no money, anyway).

It's up to you!
 

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It has been explained to me like this. One pound of body fat is approx. 3500 calories, so everyone even the thinnest tri-athlete has enough energy to ride for hours and hours. But it takes carbs to burn fat and you can only digest 50-60 grams of carbs per hour. So I try to eat/drink 50-60 grams of carbs per hour of non filling low fat and low cal foods. After my ride I eat a meal not of not only 50- 60 grams of carbs but 50-60 grams of protien. Hope this helps I has been working great for me.
 

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My CatEye HRM reads about 800 calories burned on a 26 mile ride at about 18mph taking about 1 hour and 30 minutes. This seems to be in line with Kerry's equation. My 60 milers end up being in the 1700 calorie range with more drafting and a slightly lower average speed.

Is everyone in agreement that a 500-600 calorie per hour figure is about right for a 18-20mph rider?
 
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Now I am no scientist but I believe that human efficiency ranges from about 18% up to 25% for the most physically gifted of us. That means, at best, we can transform 25% of the energy we burn into work. The rest gets lost as heat and such. So for me, I know that when my SRM tells me that I done 250 kj of work, that I have burned about 250 kcals of energy to do it. Since the conversion from kj to kcal is about 4 to 1 just changing the units on the number is an easy, but rough, way to figure out how many calories you have burned.

Having said that, I have no idea how the Polar works and how it calculates the work done and/or calories burned.
 
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