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Old 05-08-07, 12:30 PM   #1
HardyWeinberg
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calories/power output

Are power and calories constant to maintain speed in a particular gear? My wife's bike and mine have several of the same gears, and we can pedal at the same cadence in the same gear, and one of us is feeling it and the other isn't. It has to be the same power output to move the same gear at the same cadence, right? Are we each burning the same calories, and it's just much easier for one of us?
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Old 05-08-07, 12:58 PM   #2
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Are your weights and sizes identical too? And shapes - less aero will have to work harder to maintain that same cadence.
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Old 05-08-07, 01:03 PM   #3
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Also ratio of aerobic-capacity and muscular-strength comes into play as well. Guys tend to have more muscle-mass for the same lungs and can push bigger-gears at lower-cadences. Women tend to have less muscle and need to spin more for the same speed.
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Old 05-08-07, 02:35 PM   #4
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Danno, let's make this simpler. Yesterday, my wife and I took a 5 mile hike up to a mountain lake. We gained about 1250' of elevation. I wore my Polar 720i, just because. She wore her Polar A1, which just has the one number display. My HR seldom made it into zone 1, max was 104. Her HR was in the 130's and 140's. I had a 3 hour recovery walk which my Polar showed as 650 calories. She had a moderately hard aerobic workout. Did we both burn about the same number of calories?
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Old 05-08-07, 03:52 PM   #5
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Originally Posted by Carbonfiberboy
Danno, let's make this simpler. Yesterday, my wife and I took a 5 mile hike up to a mountain lake. We gained about 1250' of elevation. I wore my Polar 720i, just because. She wore her Polar A1, which just has the one number display. My HR seldom made it into zone 1, max was 104. Her HR was in the 130's and 140's. I had a 3 hour recovery walk which my Polar showed as 650 calories. She had a moderately hard aerobic workout. Did we both burn about the same number of calories?

For the most part calorie expenditure is not related to fitness level. I can be a couch potato and run for 20 minutes and burn the same as a well trained marathon runner. It will feel like evil punishment for me and just another easy jog for the runner, but the calories(assuming sex, weight, and lean mass is the same) will be the same.

The high HR and gasping just means you have fewer RBCs and your heart isn't as efficient(lack of fitness) which has nothing to do with calorie expenditure for the most part.
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Old 05-08-07, 04:07 PM   #6
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Originally Posted by Carbonfiberboy
Danno, let's make this simpler. Yesterday, my wife and I took a 5 mile hike up to a mountain lake. We gained about 1250' of elevation. I wore my Polar 720i, just because. She wore her Polar A1, which just has the one number display. My HR seldom made it into zone 1, max was 104. Her HR was in the 130's and 140's. I had a 3 hour recovery walk which my Polar showed as 650 calories. She had a moderately hard aerobic workout. Did we both burn about the same number of calories?
Probably did close to the same. The amount of power required to do the loop was probably the same provided you both weigh the same and block the same amount of air. Then the calories burnt translates from roughly a 18-20% efficiency.

But, did you both do this ride in exactly the same gearing? Looks like you may have pushed bigger gears than her, thus taxing your muscles a little more relative to your HR. Whereas she may have used lower gears, spun more to save her legs and taxed her aerobic system more.

Next time you do this exact same loop, try spinning easier gears yourself and you'll see that your HR will be higher. Since you both were doing this at sub-maximum (sub-LT) efforts, there's a lot of leeway we can have in adjusting HR and muscular-efforts up & down in a criss-cross fashion for the same power-output and calories-burnt.

Last edited by DannoXYZ; 05-08-07 at 04:50 PM.
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Old 05-08-07, 04:19 PM   #7
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Quote:
Originally Posted by HardyWeinberg
Are power and calories constant to maintain speed in a particular gear? My wife's bike and mine have several of the same gears, and we can pedal at the same cadence in the same gear, and one of us is feeling it and the other isn't. It has to be the same power output to move the same gear at the same cadence, right? Are we each burning the same calories, and it's just much easier for one of us?
In response directly to the OP, the answer is:

same cadence + same gear = same speed.

same speed + same grade + same weight + same aero situation = same power requirement

If any of the factors (like weight or aerodynamics) changes in formula 2, power requirement, and therefore Calories burned, will change.
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Old 05-08-07, 04:32 PM   #8
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Originally Posted by DannoXYZ
Probably did closeto the same. The amount of power required to do the loop was probably the same provided you both weigh the same and block the same amount of air. Then the calories burnt translates from roughly a 18-20% efficiency.

But, did you both do this ride in exactly the same gearing? Looks like you may have pushed bigger gears than her, thus taxing your muscles a little more relative to your HR. Whereas she may have used lower gears, spun more to save her legs and taxed her aerobic system more.

Next time you do this exact same loop, try spinning easier gears yourself and you'll see that your HR will be higher. Since you both were doing this at sub-maximum (sub-LT) efforts, there's a lot of leeway we can have in adjusting HR and muscular-efforts up & down in a criss-cross fashion for the same power-output and calories-burnt.
Hike, Danno, hike. Very similar cadence.

But that's what I've suspected - calorie burn about the same, since work accomplished is about the same. She just has to exert more to burn the same calories.
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Old 05-08-07, 04:43 PM   #9
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Quote:
Originally Posted by Carbonfiberboy
Hike, Danno, hike. Very similar cadence.

But that's what I've suspected - calorie burn about the same, since work accomplished is about the same. She just has to exert more to burn the same calories.

Wait! Different engines -- bodies in this case -- burn fuel at different efficiencies. Assuming you are in better condition then she is, she has to burn more calories to accomplish the same amount work/power.

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Old 05-08-07, 04:50 PM   #10
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Originally Posted by NomadVW
same speed + same grade + same weight + same aero situation = same power requirement

If any of the factors (like weight or aerodynamics) changes in formula 2, power requirement, and therefore Calories burned, will change.
Yes the amount of work done to the bicycle will be identical if the above conditions are met. However, the number of calories burnt to produce that amount of work may vary slightly.

Quote:
Originally Posted by slowandsteady
The high HR and gasping just means you have fewer RBCs and your heart isn't as efficient(lack of fitness) which has nothing to do with calorie expenditure for the most part.
Considering that the circulatory and pulmonary systems do not work for free you just pointed out the first difference. The gasping person and the normal-breather may be delivering the same amount of oxygen, on a molar basis, but the unfit persons system is working harder due to all that chest flapping.

Other considerations:

Temperature regulation – buckets of sweat don’t fall off without some metabolic cost.

Primary macronutrient providing energy – the very fit person will be burning more fat and less carbs and protein than the gasper; all while generating less lactate and waste products like urea. Even if a calorie is a calorie (debatable) the differing systemic perturbations will also have differing chemical and energetic demands.

Last edited by Enthalpic; 05-08-07 at 05:31 PM.
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Old 05-08-07, 04:52 PM   #11
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Quote:
Originally Posted by SabreMan
Wait! Different engines -- bodies in this case -- burn fuel at different efficiencies. Assuming you are in better condition then she is, she has to burn more calories to accomplish the same amount work/power.

Glenn in Omaha
Not really, humans all have roughly the same 18-20% conversion efficiency. You may be thinking of maximum power-output at LT or VO2-max which does vary between people. This is power-produced-per-oxygen consumed. But the conversion efficiency is still the same as in calories-glucose-per-Watt-produced.

So differences in fitness may result in different maximum power-output, but for any given amount of power-produced, it should be similar calories-burnt. Sure for one person it may be at 100% of their LT/TT pace, while for another it may be only 80%.
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Old 05-08-07, 05:17 PM   #12
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Originally Posted by DannoXYZ
Not really, humans all have roughly the same 18-20% conversion efficiency.
Exactly, while a 2% difference may seem small consider a person who originally is 18% efficient who then somehow increases their efficiency to 20%. That translates into a ~11% increase in performance, an enormous amount when compared to other training adaptations.
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Old 05-08-07, 07:06 PM   #13
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Originally Posted by Carbonfiberboy
Hike, Danno, hike. Very similar cadence.

But that's what I've suspected - calorie burn about the same, since work accomplished is about the same. She just has to exert more to burn the same calories.
That's not at all what I got from reading the above.

Work accomplished can only be the same if they are both identical in stature, weight, and shape (would make for an odd-looking couple).

If either one is heavier, and there were hills, that person almost certainly did considerably more work, as in more energy expended per unit time. That person would also (likely) have to burn more calories, unless the heavier person was VERY, very fit and the lighter person was VERY, very unfit, and the weight differential was not very great.

Stature and shape also play a part, but to a lesser degree (that's why there are 6' top-level pro cyclists (Jan, Bobby Julich), but no 200lb-ers).
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Old 05-09-07, 06:56 AM   #14
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Originally Posted by Enthalpic
Yes the amount of work done to the bicycle will be identical if the above conditions are met. However, the number of calories burnt to produce that amount of work may vary slightly.



Considering that the circulatory and pulmonary systems do not work for free you just pointed out the first difference. The gasping person and the normal-breather may be delivering the same amount of oxygen, on a molar basis, but the unfit persons system is working harder due to all that chest flapping.

Other considerations:

Temperature regulation – buckets of sweat don’t fall off without some metabolic cost.

Primary macronutrient providing energy – the very fit person will be burning more fat and less carbs and protein than the gasper; all while generating less lactate and waste products like urea. Even if a calorie is a calorie (debatable) the differing systemic perturbations will also have differing chemical and energetic demands.
But is it a significant difference? NO.


It is the cruel joke for the fat unfit person trying to lose weight. They have to feel practically dead to burn roughly the same calories as the fit person who feels at worst, invigorated.

If it wasn't the case there would be essentially no fat people because no matter how fit or unfit you were, calorie expenditure would balance itself out.
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Old 05-09-07, 07:57 AM   #15
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Originally Posted by DannoXYZ
Not really, humans all have roughly the same 18-20% conversion efficiency. You may be thinking of maximum power-output at LT or VO2-max which does vary between people. This is power-produced-per-oxygen consumed. But the conversion efficiency is still the same as in calories-glucose-per-Watt-produced.

So differences in fitness may result in different maximum power-output, but for any given amount of power-produced, it should be similar calories-burnt. Sure for one person it may be at 100% of their LT/TT pace, while for another it may be only 80%.
Let me take a different example. I am not a very graceful swimmer. I tend to flail about. In swimming a lap in the pool a smaller portion of the energy I expend goes into moving me foward, as compared to a master swimmer swimming that same lap. I must expend more energy to complete the lap than the master swimmer.

Probably, this example does not transfer very well to biking, since most bikers (even me) don't flail that much in riding

Glenn in Omaha
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Old 05-09-07, 08:06 AM   #16
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Originally Posted by NomadVW
In response directly to the OP, the answer is:

same cadence + same gear = same speed.

same speed + same grade + same weight + same aero situation = same power requirement

If any of the factors (like weight or aerodynamics) changes in formula 2, power requirement, and therefore Calories burned, will change.
You left off rolling resistance in your power equation. Different tires and pressures can make a significant difference in power requirements, especially at slower speeds where aerodynamics play a lesser role.
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Old 05-09-07, 09:29 AM   #17
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Originally Posted by SabreMan
Let me take a different example. I am not a very graceful swimmer. I tend to flail about. In swimming a lap in the pool a smaller portion of the energy I expend goes into moving me foward, as compared to a master swimmer swimming that same lap. I must expend more energy to complete the lap than the master swimmer.

Probably, this example does not transfer very well to biking, since most bikers (even me) don't flail that much in riding

Glenn in Omaha

Swimming is a bad example because swimming isn't as much about exertion but rather form. I may be treading water and burn as many calories as the guy doing laps. Forward movement is highly dependent upon technique in swimming. The fastest swimmers, though fit, are the fastest because each stroke is more efficient(greatest distance per energy spent) than the next guy's.
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Old 05-09-07, 11:36 AM   #18
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Originally Posted by SabreMan
Let me take a different example. I am not a very graceful swimmer. I tend to flail about. In swimming a lap in the pool a smaller portion of the energy I expend goes into moving me foward, as compared to a master swimmer swimming that same lap. I must expend more energy to complete the lap than the master swimmer.

Probably, this example does not transfer very well to biking, since most bikers (even me) don't flail that much in riding

Glenn in Omaha
True, if you've got a highly inefficient pedal stroke where you're pushing down at the bottom and stretching the crankarm, there's a lot of wasted energy that doesn't go into moving you forward. Or if you've got a lot of upper-body movement bouncing and rocking around and have to yank on the bars to compensate.

That only means you'll spend more calories covering the same distance, and you'll also burn off more glucose as well. However, the conversion efficiency of glucose-calories burnt to watts-produced is still the same.

In this case, I suspect the heavier person who blocks more wind actually has to develop more power and burn more calories during that ride.

Last edited by DannoXYZ; 05-09-07 at 11:44 AM.
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Old 05-09-07, 12:50 PM   #19
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Originally Posted by SabreMan
Let me take a different example. I am not a very graceful swimmer. I tend to flail about. In swimming a lap in the pool a smaller portion of the energy I expend goes into moving me foward, as compared to a master swimmer swimming that same lap. I must expend more energy to complete the lap than the master swimmer.

Probably, this example does not transfer very well to biking, since most bikers (even me) don't flail that much in riding

Glenn in Omaha
Quote:
Originally Posted by DannoXYZ
True, if you've got a highly inefficient pedal stroke where you're pushing down at the bottom and stretching the crankarm, there's a lot of wasted energy that doesn't go into moving you forward. ...
not to be argumentative
but SabreMan is quite right - even for cycling, especially for cycling
while everyone considers 'efficiency' as something at the cellular level, the real world really is much more.
His swimming example does hold water in cycling as well. Muscle contraction, to create rhythmic movement as a pedal stroke, opposes the contraction cycle of other muscles. The total efficiency of the system is how well they interact as well as their individual efficiences. Thats a major reason why athletes 'train'. And if someone's not sure about swimming relative of 'exertion' to 'form', jump in and do a few laps.
'Form' or efficiency in anything (Fosbury Flop) takes you to higher levels of performance for the same 'expenditure' of work.

Easily demonstrated by any rider if they cover a 'course' at a set/constant speed using different cadences.
There's no question the same rider, riding the same 'course', will do less 'work' than he/she did sometime prior to an extended training period, be it either weeks or months.
I can try to rummage thru some of the older studies which have clearly ID'd this. But subjectively this is proven every day by millions of riders and other athletes.
Running, riding, swimming - you name the activity - efficiencies vary for a person as well as between people.
For the OP, if its important, your wife and you will have different 'power' curves and different expenditures to cover the same 'course', even done side by side.
This is true for every known engine, especially the human one.
And, even though some speak of the sameness of cellular efficiency and chemistry, that will also vary greatly under changing temps, pH and a bunch of other determining factors.
We, as orderly humans, all would love to have some 'equational' correlation thats simple and direct. But I don;t think thats in the cards considering the complicated machine being considered and the huge number and variation of the variables involved. Ballpark is prolly the best one can have, outside of a strictly controlled environment.
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Old 05-09-07, 01:48 PM   #20
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And if someone's not sure about swimming relative of 'exertion' to 'form', jump in and do a few laps.
You have obviously never been trained to swim by a decent coach. Sure it takes effort to swim, but beyond a certain point, because water is so incredibly dense, you have to have an efficient gliding stroke. You can kick and kick as hard as you want, but you can be easily passed by the guy with the perfect stroke who is barely exerting himself.

Swimming fast is a compromise between the power of the stroke and the number of strokes. The goal is to find that perfect ratio of least number of strokes that it takes to get the fastest time.
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