That rowing site did include a term for base metabolism. So the Burn :: Power equation should look more like

B = m + (a * P)

When you are just sitting there you still burn some calories! As you start pedaling, sure your heart and lungs work along with your legs. But if the extra calories burned by heart and lungs (diaphragm, intercostals, etc.) is proportional to the calories burned by your pedaling legs, then the power ::burn still holds.

Now, if some acrobat is holding dumbbells while riding a bike and starts doing reps of various lifts, seems clear that calories burned will no longer have such a strict relationship to power at the bottom bracket. So the relationship surely has limits.

What I'm suggesting (but not stating is true) is that "fit" people make power using less energy. So your "a" would change depending on the state of the person.

Since we are in the suggesting mode, I suggest that the difference, if there is any, is negligible in whole grand scheme of exercise/weight loss calories counting - say 10 calories/hr. For example, an unfit person may have a layer of fat and therefore will prob feel warmer while exercise and need to sweat a little more. But that's still only an extra 10 calories/hr more.

This looks like a nice overview of the physiology involved:

http://highered.mcgraw-hill.com/site...ample_ch03.pdf

But I didn't see our question addressed squarely. A couple things are clear enough: with increased fitness one can produce more power and burn more calories. (see pg. 16 for a plot of VO2 max increasing with training.)

Also, poking around the internet, the typical overall efficiency of turning food energy into mechanical energy is estimated at about 25%. That is already quite a high number. Maybe it can budge a bit, but it really can't get much higher.

Here is a relevant post from Friel:

http://www.joefrielsblog.com/2012/01...wer-meter.html

Hi.
,
In the big scheme of things all of the arguments about efficiency are irrelevant.
Its ~ 25% and doesn't change much what ever you do, though I concede
very small improvements may be possible with good conditioning.

In terms of burning calories to lose weight its irrelevant. In terms of calories
sticking with the same courses over a period, you will burn more calories as
you get fitter, whether you lose weight or don't , but doing to it lose weight,
and losing weight won't reduce calories burnt, you will just be faster, because
average power output will continually improve with fitness almost by definition.

FWIW very poor initial technique on a bike will inevitably burn more calories,
but in the longer term that becomes irrelevant, most people can ride a bike,
and anyone that does it regularly for fitness soon becomes efficient at it.

In terms of calories it doesn't matter, you just get a little faster. Over a given
course, as you get faster with more power output the consequences of the
aerodynamics mean you always burn more calories over your shorter time.

rgds, sreten.

The biggest difference is aerobic vs lactate as discussed a couple of pages back.

A fit rider has strong lungs and enlarged heart that sends more blood through the system with each stroke, and a dense capillary system in leg muscles that delivers oxygen to muscle cells. The 25% efficiency above (actually 18-22% is quoted more frequently) corresponds to the case of properly oxygenated muscles. An unfit rider may not be able to push with the same power without running out of air. He will temporarily go at reduced efficiency and quickly collapse.

When comparing riders working at intensity levels that they can maintain for 2 hours straight, the fit rider and the unfit rider do not differ significantly in their efficiencies.

Technically yes. I burn 60 calories per hour when sleeping or watching TV. I would probably burn another 1-2 calories if I had extra 10 lbs of fat. I may burn as much as 10 calories per hour if I start weight training and gain 10 lbs of lean muscle (though this last number is very controversial). On top of that, I burn 400 to 600 calories per hour during vigorous cycling.

[QUOTE=Mobile 155;15670085]My 5 year old daughter often calls me "dude" and she does not fit into any of these groups. Also, I don't use the word myself so I have no clue where she got it.

[QUOTE=hamster;15678535]The biggest difference is aerobic vs lactate as discussed a couple of pages back.

A fit rider has strong lungs and enlarged heart that sends more blood through the system with each stroke, and a dense capillary system in leg muscles that delivers oxygen to muscle cells. The 25% efficiency above (actually 18-22% is quoted more frequently) corresponds to the case of properly oxygenated muscles. An unfit rider may not be able to push with the same power without running out of air. He will temporarily go at reduced efficiency and quickly collapse.

When comparing riders working at intensity levels that they can maintain for 2 hours straight, the fit rider and the unfit rider do not differ significantly in their efficiencies.



Technically yes. I burn 60 calories per hour when sleeping or watching TV. I would probably burn another 1-2 calories if I had extra 10 lbs of fat. I may burn as much as 10 calories per hour if I start weight training and gain 10 lbs of lean muscle (though this last number is very controversial). On top of that, I burn 400 to 600 calories per hour during vigorous cycling.

I think we are talking both Technically and medically according to both Harvard and Mayo. But we aren't that far apart. I was simply stating the California idiom is Dude, Bro, or Man. Not that we all use it. But never Bubba. Well Maybe Oildale does. Desert Racers, dirt Bikers, and MTBs still us it as in "Dude you shredded that ride. I don't know if your 5 year old is either of those but I doubt if she calls you Bubba. :lol:

No. Or at least, not significantly. Fit people can maintain higher power outputs for longer because they are fit. But the higher power outputs require proportionally higher energy expenditure. Watts are watts, and their relationship with calories is constant.

Athletes aren't superior to others because they conserve energy, they are superior because they burn more of it. As a sideline on this, the high cadences typically used by racing cyclists are very energy-inefficient. There is an energy cost to simply spinning one's legs faster, and the most efficient cadence terms of oxygen burned for a given power output is about 60 rpm. But higher cadences reduce the fatigue on the muscle fibres, and the fit cyclist has power to burn, so to speak - the additional energy and O2 demands are pretty much immaterial, they can sustain them for hours. So what is inefficient in terms of conserving energy (and burning calories) is nonetheless more effective at winning races.

To me this just sounds too strong. Sure, they are both physical measurement units and so there is a strict mathematical relationship. But if we look at the rate of food burning on the one side and the rate of mechanical work being done on the other, there is physiology in between, and that is not any sort of strict mathematical beast. A person is a kind of engine just like an automobile engine, converting chemical energy to mechanical energy. An automobile engine's efficiency, i.e. miles per gallon, can vary quite a bit.

If a higher cadence is less efficient and there is an energy cost just to spinning one's legs, then actually a high cadence should burn more calories for the same wattage delivered to the cranks.

Hi,

But unlike a car engine which only approaches its maximum efficiency
at full throttle, a mammals body maintains its maximum efficiency
over a wide range of power outputs.

It may sound too strong but effectively it isn't, as the differences
are too small to worry about. Your imagined differences simply
don't exist, except for very small power outputs.

rgds, sreten.

Yes, it does, but you are now talking about a different thing. This has nothing to do with whether fit athletes burn fewer calories per watt than unfit athletes. As sreten has explained, this is just not so. Now we are talking about whether there is, for any athlete, a particular cadence at which one gets the best bang for the buck. Yes, there is; but it isn't dependent on fitness. My point about that was that the fit athlete has an advantage because they can afford to "waste" energy - burn more calories, not less - in order to spare their muscles.

I am just trying to draw a logical distinction. On the one hand, there are a variety of units one can use to measure a power flow, e.g. watts, horsepower, calories per minute, etc. The ratios between these is not an empirical matter, at least not any more. Once upon a time a calorie was the amount of heat required to raise the temperature of a gram of water from 0 to 1 degrees Celsius or some such, but by now I expect that a calorie is defined to be so many Joules.

By conservation of energy, one way or another the energy flowing into some process has to be stored or flow out somehow but there can never be any net increase or decrease. Muscles take in however much chemical energy and out comes all sorts of things - energy in chemical products, mechanical work, heat, energy gained or lost in restructuring tissue. Anyway the ratio between chemical energy in versus mechanical energy out, that is not anything fixed mathematically or logically or semantically. That is a ratio with empirical meaning and actually not such an easy thing to measure precisely.

For losing weight, really exercise doesn't do that much. Avoid refined carbohydrates and cut down on rich fatty foods like cheese and meat. Eat whole grains and fruits and vegetables and nuts. The game is to work with one's natural feedback system, so one's sensations of hunger and satiation are appropriate to one's actual caloric needs.

Planning for snacks on a long ride... sounds like you just have to know your own digestive system and what it can handle. And don't ride so fast that you will outpace digestion plus fat burning!

One of the fun things about biking though is that it provides a nice window into the engine aspect of the body. It is fascinating to learn about physiology, about energy stores and how energy flows and gets converted from one form to another etc.

So that's why I am not comfortable with the idea that food calories in versus mechanical work out is any sort of rigidly determined relationship. That seems to close off physiology, to reduce it to some fixed simple formula. I like how cycling can actually open up physiology and reveal some of its fascinating complexities.

What's interesting to me is the varying efficiencies involved in riding a bike. Of course the biggest part is how power at the crank turns into progress down the road. But the physiology of getting power to the crank, that is a rich topic too.

Given that there are more and less efficient or effective ways to get power to the crank, then the next question becomes: when and how does a person pick one or another way?

"Fitness" is a funny term. Probably it just means "proficient at a task". Proficiency could come from various aspects of physiology or from good habits built up through training or maybe just some good knowledge picked up from experience and from the experience of friends.

Anyway thanks for sharing your own expertise - I learned a lot!

Hi,

Fair enough, but how effective you are at burning calories in not the same as efficiency.

Exercise does do a lot regarding losing weight. You can starve yourself to lose weight
but you'll feel awful and probably lose a fair amount of muscle mass along with the fat.

Exercise makes you feel better and raises your overall metabolic rate. It also makes
you instinctively more particular about your diet. If you cycle to get fit and stay fit,
with a decent regime per week, you will lose about a pound a week of excess weight.

rgds, sreten.

That's a fact! Putting in time and effort, that's the way to burn calories!

Here was my route today:

http://www.mapmyride.com/us/woodstoc...route-51584600

I think the calorie estimator at mapmyride is really stupid. OK, I averaged 9 mph! Hey, and do the math: how come, if my starting elevation is 575 ft and my max elevation is 1795 ft... shouldn't my total climb be at least 1220 ft? But they say 1120! Plus nowhere do I get credit for a 40 lb bike plus 20 lb of who knows what in my bags. I think I burned a few calories today!

You guys keep saying this, but this isn't quite true. The question I have is this: How untrue is it. Are we talking about a sub 1% effect or a 10% effect. And as far as I can tell, I don't know that anybody who has yet chimed in on this thread (myself included) is qualified to answer this question.

My guess is that there is so much noise both in measurement and also trying to control all the variables that the real answer is not known with a whole lot of accuracy.

This is alluded to in that textbook chapter I linked to above. Aerobic metabolism can be measured with the conversion of oxygen to carbon dioxide. But other processes leave waste products in the body for much longer times so that is hard to track. Another odd puzzle is exactly how to disentangle basal metabolism from metabolism directed to mechanical work.

It seems clear enough that trained athletes can burn calories and produce mechanical work at a rate maybe 4x that of an ordinary person - comparing Bradely Wiggins at 480 Watts to my 120 Watts. Chasm54 has a nice example of where such an athlete might be so skillfully trained that he can actually use less efficient pedaling as a way to avoid muscle strain. The difference in efficiency between Mr. Wiggins and myself... probably the error bars in any kind of statistical estimate will include the 0 value. Fun to explore the mechanisms involved, but ... it'd be fun to see what the diet of Mr. Wiggins looks like - how does he manage to eat enough to burn so much?!

Hi,

Nothing in science can be exactly true or exactly exact. You can bet though if efficiency
varied by 10% you wouldn't have any problem finding information about it, and why.

Books would be written on training to maximise efficiency.

Simple fact is you are talking exactly the same chemistry in all people (and mammals)
in tiny muscle fibres optimised pretty much over millions of years for maximum
efficiency over a wide range of power outputs. The ratio of slow twitch to types
1 and 2 fast twitch fibres varies between people and is affected by conditioning.

Fundamentally two people of the same size and weight, one fit, the other not,
but the unfit person only using slow twitch within his limits, going at the same
rate will use up the same* calories. There is no reason to assume otherwise.

rgds, sreten.

* Of course not exactly the same, but not enough difference to care.

A little known fact I picked up somewhere is the optimum rest to
work ratio for the maximum power output of a muscle is ~ 6:1.

Bicycle cranks are almost ideally suited to this regime if you only
really apply your muscles for ~ 50 degrees of the cranks rotation,
noting it is not the same ~ 50 degrees for all the various muscles.

(It said 6:1 and 60 degrees, but that is 5:1, dodgy maths.)

Here are some tips from Mr. Wiggins:

http://www.menshealth.co.uk/fitness/...radley-wiggins

The meal before bed is the most important one - presumably because it's the only one where there is the time and rest for proper digestion! He says he eats 7000 calories a day and burns 8000 - during the race.

Hi,

The last thing mere mortals should ever do is take any notice
of the habits and practises of the cycling elite, its pointless.

rgds, sreten.

Not quite. I'll bet his pedalling action is mechanically very efficient, it is the choice of a fast cadence that raises the calorie consumption.

He doesn't, all the time. But most of the time he is riding well within himself, getting most of his fuel directly from fat stores, and even the skeletal Bradley has enough body fat to fuel his efforts for days. One kilo of fat = 9000 kcal.

This statement is new age content-free crap. Moving on.

But it is everywhere. I can find lots of web sites and books where people say exactly this. They say you are supposed to mix up your routines to make sure you are using different muscles for exactly this reason.

I can also find lots of websites where people say that there is no difference.

I asked the personal trainer at work and he didn't know. He asked his colleagues and told me that yes it is true that more fit athletes are more efficient (calories in to power out) and it is a 10-20% effect. This is consistent with what I thought, but I'm sure I could talk to other people in the field and get the other answer as well.

Great. So, what have we learned?

That we (still) need somebody qualified to answer and that we don't know.

Wow! And you're the guy suggesting OTHER people don't understand basic physics 101? Energy and power are pretty directly related. If there's anything to discuss its the energy reserves actually available and the body's ability to recover and replenish them.

Starting with a higher capacity battery that can support a higher current draw isn't about effeciency - its about starting with more energy in the first place and being able to tap into it more effectively.

In your analogy, it isn't only whether or not there is a higher capacity battery, but also a higher efficiency motor attached to it.

We've already established that the "efficiency" of the human body is no where near 100%. So it is not the case of power in = power out. And we've already discussed that making power under different types of conditions (e.g., aerobic versus anaerobic) has differences in efficiencies. So, given all this, you find it impossible to consider that there might be differences between fit and non-fit individuals?

I think "higher efficiency motor" isn't the appropriate term. Biochemically we are all the same and being more fit doesn't alter any of that. The better term would be "more powerful motor" because it can consume store fuel more rapidly (via more mitochondria, more red blood cell, etc). That said, I'm sure there are small differences. An unfit person would likely have a layer of fat, which makes him feels warmer. So additional energy will be needed for cooling. But that's really tiny.