Training & Nutrition - Calories burned

I have an HRM that gives me a "calories burned" . Now, I know this isn't hyper-accurate since it doesn't know my wieght or max HR, but I wonder if I can trust its result within a reasonable margin of error. For example, it says I burn about 5,000 calories on a 3:30 ride at about 70% of my max HR. I read an article from Bicycling Magazine that says this number should be closer to 3,000 but it didn't mention anything about HR.

I guess my question is: how does calroies burned vary depdning on the person and the exercise.

Well- the amount of calories burned varies depending on a lot of factors- the intensity of the exercise, the length of the time you're exercising, the amount of muscle you have, etc...

At aerobic intensities, the calories burned come primarily from fat metabolism. At anaerobic intensities, the calories burned come primarily from carbohydrate metabolism. At 70% max heart rate, the amount of calories you did burn would come primarily from fat metabolism. BUT I do not think that a 3:30 ride at 70% would come even close to burning 3000 calories. A ride like that would burn about 7- 8 calories a minute (see "The Heart Rate Monitor Book for Outdoor and Indoor Cyclists", by Edwards, Reed for the average breakdown of calories burned at different % heart rate maximums), yielding 1470- 1680 calories. Approximately 15% of the calories burned would come from carbohydrate metabolism, 80% would come from fat metabolism, and 5% would come from protein metabolism.

The best way to find out how many calories you were burning is to go to a performance lab (sound familiar? :p ) and have them test you for your heart rate ranges, max heart rate, anaerobic threshold (also known as lactate threshold), and to check on where you burn carbohydrates primarily as your fuel source and where you burn fat primarily as your fuel source. A comprehensive test like this would give you the answers you needed.

I don't trust heart rate monitors that spew out arbitrary numbers- seriously, I think they're the newest doodad gimmicks out there to get people to buy their product, and they don't tend to be very accurate, as they depend on generalizations gathered to produce arbitrary numbers.

Koffee

Try this out.
Calorie Burner (http://www.caloriesperhour.com)

Pretty cool. Thanks!

My HRM has a similar calories burned estimate, but also includes the ability to enter the user's weight, age, maximum HR, etc.

This probably enhances the accuracy of the estimate considerably, though to what extent I can't say for sure.

You might double check your monitor to see if it has a similar data entry feature.

Mine has gender and weight (not age, interestingly enough). I guess it has a formula and I can only assume it uses a default max HRM... but it came with a free bike mount! :D

Wow, did you see all the categories on the page?

Hmmmm..... the page comes up blank for me when I click on the link.

:confused: What am I missing here? Do I need some kind of java applet enabler or something?

Koffee

I've been using this site for about 1 year now and at least it is consistant.

This morning I did a 1:48 ride at 17.6 mph, it says I burned 2351 cals. This site also jibes very well with the one on Bicycle magazines web site.;)

Burn'em baby!!!!:beer:

Well, the Death Ride was about 5,000 Cal for me so I think your estimates are a bit high. I use an SRM and get my work in kJ. A flat terrain 1:48 ride at 17-19 mph would be about 1100-1200 Cal.

Calories during exercise come from various forms of storage but what's relevant at the end of the day is how much you eat versus how much you use. If you are in caloric deficit, it will come out of your fat stores. If you you are in excess, it will be stored as fat regardless of how long you spent riding in your "fat burning zone."

Originally posted by TriDevil
Try this out.
Calorie Burner (http://www.caloriesperhour.com)

That sucks! It tells me I'm ONLY burning 54 calories for 30 minutes of vigorous sexual activity. I can do that having a Tic-Tac. :rolleyes:

Originally posted by TriDevil
Try this out.
Calorie Burner (http://www.caloriesperhour.com)
I love that site, thanks. :)

Well, I have some background in ecological energetics.

It is rather tough, experimentally to determine calories burned. I doubt very much that any local lab near you would have the facilities or expertise to do it.

What most people do is come up with estimates based on assumptions and who knows if those are accurate of not? I have read that 30-55 calories per mile (light weights 30 and heavy weights 55) is a decent guess and it seems as good as any of the others. I think the above figure was come by not experimentally by measuring calories expended but by using the laws of physics to make an estimate.

Don't believe heart rate. I have a friend and he is the same weight as I am. I can drop him and his heart rate can be 20 beats higher then mine! So heart rate is nothing but a guess. It can be thrown off quite a bit when one person has a larger heart then the other, for example.

The way to tell experimentally is to measure the CO2 given off by the cyclist and the 02 consumed. You need to measure both because Carbohydrates and Fat produce different amounts of C02 on burning for different energy yields. Getting the same energy by burning fat takes twice the oxygen as burning carbohydrates. Fat has advantages though, the energy content in fat is much higher on a weight basis. If we stored all our calories as carbohydrate we would weigh much much more - not only is carbo twice as heavy per unit energy but it requires about water (about 4X it weight) for storage making it 10X as heavy as fat per calorie.

Of course, an even better way to estimate calorie consumption would be by using radiolabeled stuff to really zoom down on things. But I don't think anyone wants to know THAT badly that they are willing to eat radioactive food. And even if they were, I wonder if any experimenters would be willing to fool with it, that is assuming that they could get such a thing green lighted by the committee that OKs these things (and this one has a snowball's chance and properly so).

Now, burning fat tends to occur at the lower end of the aerobic zone. As you push harder and harder, a higher percentage of carbohydrate is burned. Maybe someone has done a study on just what the curve is but I bet it varies widely for individuals and widely based on their training. A sprinter will not burn fat much and a marathon cyclist should burn fat well. I would suspect that out of condition people will tend to burn little fat.

The more intense the exercise, the less proportion of energy comes from fat. However, the harder you go, the more calories you expend and that will come out of your fat stores later in the day. Though it's not possible, even if you burned no fat during a workout, you will afterwards because the energy has to come from somewhere (fat or eating more food).

You'll burn more fat riding X hours at time trial pace than dawdling in the mythical "fat burning zone" for the same amount of time.

Don't believe heart rate. I have a friend and he is the same weight as I am. I can drop him and his heart rate can be 20 beats higher then mine!

I'm not sure that's a fair statement. If your level of fitness is higher than his, you will be able to acheive more with less effort. I can smoke a fat slob who's been sitting on the couch for the past year w/o breaking a sweat, but he will burn more calories than I will because it requires more "work" for him to move (one reason being that I simply weigh less). Heart Rate is an *excellent* indicator of "fat burning". Your body uses different sources of energy based on the level of intensity. To say that heart rate is not a good indicator shows that you don't pay much attention to clinical trials and studies...

If heartrate is an excellent way to estimate calories burned then tell me how many calories I burn on a 128 minute ride with a average HR of 146. Assume that I weigh 164 lbs.

Estimating calorie consumption by heartrate makes too many assumptions to be accurate.

Squint, when was the last time you got tested for your accurate heart rate percentage values, and when you did get tested, what did they say was your anaerobic threshold, and where do you burn calories from fat vs. carbohydrates at different percentages, and finally, can you let us know what they said you were burning in calories?

If you at least got tested for your accurate heart rate percentage values, we could answer that question with at least some approximation, but without even this information, it is impossible to estimate anything.

I can tell you that you DID burn calories- that's about it. :(

Koffee

Originally posted by CarlJStoneham
I'm not sure that's a fair statement. If your level of fitness is higher than his, you will be able to acheive more with less effort. I can smoke a fat slob who's been sitting on the couch for the past year w/o breaking a sweat, but he will burn more calories than I will because it requires more "work" for him to move (one reason being that I simply weigh less). Heart Rate is an *excellent* indicator of "fat burning". Your body uses different sources of energy based on the level of intensity. To say that heart rate is not a good indicator shows that you don't pay much attention to clinical trials and studies...

Carl, I am not saying that heart rate monitors are not good training devices. They can be very useful when used properly.

You talked about heart rate as an indicator of burning calories. Obviously, if two riders of the same weight are riding at the same speed and the same conditions and similar bikes, they should be burning about the same amount of calories. But if one rider has a heart rate that is far lower then the other, and this can and does happen, then that shows that you can not use heart rate to estimate calories burned. Get it?

And that's where testing comes in- because no two people are EVER the same, no matter what scenarios you create. Two riders of the same weight riding the same speed under the same conditions having similar bikes will not be burning the same amount of calories, like you said. At the same time, if you would simply call a performance lab and ask them to test you, you will find that they can CERTAINLY test you based on your heart rate ranges and find out how many calories you burn, as well as at what % of your max heart rate you are burning those calories primarily from fat and what % of you max heart rate you are burning those calories primarily from carbohydrates.

If you give me an idea of what city you live in, I'll find a performance lab for you that you can at least call to have your basic questions answered. If you're interested, drop me a PM.

You're almost there- you do have half the story right, you just need some filling in the blanks done.

Koffee

Originally posted by Koffee Brown
And that's where testing comes in- because no two people are EVER the same, no matter what scenarios you create. Two riders of the same weight riding the same speed under the same conditions having similar bikes will not be burning the same amount of calories, like you said. At the same time, if you would simply call a performance lab and ask them to test you, you will find that they can CERTAINLY test you based on your heart rate ranges and find out how many calories you burn, as well as at what % of your max heart rate you are burning those calories primarily from fat and what % of you max heart rate you are burning those calories primarily from carbohydrates.

If you give me an idea of what city you live in, I'll find a performance lab for you that you can at least call to have your basic questions answered. If you're interested, drop me a PM.

You're almost there- you do have half the story right, you just need some filling in the blanks done.

Koffee, I said that 2 riders of similar weight, with similar bikes at the same speed will be burning similar amounts of calories. I did not say the SAME amount of calories. I think you misunderstood me.

I was thinking of a situation of a friend of mine who used to ride with me. We are the same height. I think I weighed 190 and he weighed 200. My bike is about 1 lb heavier then his. And we were riding side by side at the same speed with the same position on our bikes (both with hands on the hoods). So we were probably burning similar levels of calories because we were doing similar levels of mechanical work - moving objects of similar weight through the air at the same speed.

My point on the heart rate deal is that in this situation, I would be at say 150 and my friend at 175. I could drop him when he was drafting me (so I was expending signicantly more energy) and his heard rate would be higher then mine! So obviously an estimation of caloric consumption based on weight and heart rate is flawed. That was my point. I think we are in agreement with the basic point. We may have differences on the details.

Now you talk of labs that can determine one's caloric consumption based on knowing one's heart rate and heart rate at anaerobic threshold. I don't see it.

You can have 2 riders with the same heart rate and anaerobic threshold but they can still vary. Muscle activity under exercise is limited by training and oxygen delivered to the muscle. One rider could have a heart with a larger stroke volume and have a higher concentration of hemoglobin in their blood giving them the ability to deliver significantly more oxygen to their muscles at a given heart rate. Using heart rate information and knowing the heart rate at anarobic threshold would not give one that information. Absent some sort of direct measure of caloric consumption such of generation of CO2, I just don't see a lab being able to do more then make a guesstimate. The estimate might be informed but it would not be an actual measurement and there is a big difference. Do you know of some web sites that give the methodology these labs use so that I could read them?


Koffee

Obviously, if two riders of the same weight are riding at the same speed and the same conditions and similar bikes, they should be burning about the same amount of calories.

Again, you did not take fitness level into account. If I ride w/ someone my size who's not "in shape", they will require more work to acheive the same speeds (whatever) I'm keeping. More work = Higher HR = more calories. At the end of the ride, if they kept up with me, they would have burned more calories because their body is a less efficient machine than mine. Heart Rate is the closest indication of work most of us can get (w/o spending much $ on a wattage device) to work done.

Remember, Calorie (?kilocalorie?) is ultimately the amount of energy "required to raise the temperature of one kilogram of water by one degree at one atmosphere pressure". I'm not saying that HRMs are pure definers of calories burned, but they DO tell give me a relative sense (I'm burning more calories at 80% than 60% max). My original post was to determine whether my HR was accurate or not (it wasn't, but once I determine the margin of error, I can use it to more closely determine calories burned).


tell me how many calories I burn on a 128 minute ride with a average HR of 146. Assume that I weigh 164 lbs
Again, I would need to know your max HR and level of fitness before I could estimate. HR =146 for you might be 16mph. For me, it's 14...

I know HRM's are not an objective measure of calories burned, but given the correct parameters, they can be quite useful in determining this.

Back then my max HR was probably 197 +/- 2 and I was fairly fit.

If you want to know what the margin of error your HRM's calorie consumption estimates have, I would say at least 300%. 5000 kcal in 3:30 is 1661 watts or about 4 times the power output of a world class pro.

5000 kcal in 3:30 is 1661 watts or about 4 times the power output of a world class pro
You're just not getting this, are you? Watts is an instantaneous masurement of power/work potential, not work *done*. In order to speak about a world-class cyclist, you need to speak off watt-minutes or kilowatt-hours, etc (much like an electric bill). Armstrong's peak output is about 400 watts, but this is at a single point in time. IF he could sustain this for an hour (impossible), his output would be .4 watt-hours (enough to power a 100-watt bulb for four hours (I think I have that right, but it can get confusing)). You can't just convert calories to watts (if you think you can, show me the formula *with units*) because calories burned is not an instantaneous measurement. Armstrong needs fewer calories to generate a given wattage over a given time period than I do because he's a far more efficient "machine" than I am. If it was a 1:1 ratio regardless of fitness (which it's not), Lance would need roughly 25,000 calories for one stage of the TdF which would mean he'd have to spend the whole day eating and would have no time to ride. Lance's caloric intake for a day is about 3x mine (I think I read somewhere that he takes in 6,000/day) but his potential power output is probably 10-20x mine. See why calories are not directly proportional to power?

As for your numbers, what was your level of fitness when you rode @ an avHR of 146? Were you only able to 12mph? 14? etc... A month ago, at 146, I could only have done 13mph. now I can do 15 (though this is somewhat unfair since I've upgraded to clipless pedals which increase the efficiency of my stroke w/o requiring an increase in exertion).

Also, my HRM was off by about 20-30%, not 300%. Where on Earth did you get that number? Heck, you burn a few hundred calories a day just digesting food! (When I said kilocalories, I was trying to remember how it works. I think 1 Calorie is 1000 calories (note the "C" vs "c") but I can never keep it straight.)

Anyway, pulling this all back to the HR, my contention is that you will burn roughly the same number of calories at a given HR over a given stretch of road, even if you up your speed because as you become more fit, you can create more power with the same amount of "fuel". Of course, I could be wrong (I don't know everything) but you're going to have to "prove" it.

Estimating calorie consumption by heartrate makes too many assumptions to be accurate
I guess I'm not disagreeing with this, per se, but I think using HR to estimate calories burned is is not as inaccurate as you're implying.

Actually Squint, ignore my question about your fitness level, since I'm kind of maintaining the HR tends to even that out.

At 164lbs @ 146bpm over 2:10, I'd say you burned about 1500 calories, based on:

Me: 4000 calories (adjusted based on research showing my HRM to be off about 20%) @ 75% max over 3:30 at a weight of 260

You: 75% max over 2:10 (60%) at a weight of 164 (65%)

Is that about right?

Of course, things like weight to power have a difference, but generally...

For that ride, my SRM file says it was 1054 kJ or about 1000 Cal when you figure 22-25% efficiency. Using a powermeter to determine calories consumed makes only one assumption, that of efficiency.

The problem with HR is that it does not correlate with work. It's individual. Whether you're fit or not, your LT heartrate, max HR, etc., will not change that much. Two people can have the same fitness level, weight, age, etc., but completely different heartrates while riding the same speed.

One thing- if two people are riding the same speed and have different heart rates (I assume you mean percent of maximum heart rate), then they have different fitness levels. If they had the same fitness level, they'd be at the same heart rates.

It is so true that heart rates ARE individual- which is why folks need to get tested. People who just guess or go by mathematical equations, or go by some watch that gives you a generalized approximation do themselves a big disservice by NOT getting professionally tested.

A partial answer to the question posed in the original thread starter can be found here:

http://drlenkravitz.com/Articles/caloricexp.html

Dr. Len Kravitz is one of the most active professors out there who publishes, performs research, and lectures regularly about exercise- and he's really GOOD.... his articles are interesting and definitely readable, and he addresses caloric expenditure and fitness level in the aforementioned link.

Koffee

Two people can have the same fitness level, weight, age, etc., but completely different heartrates while riding the same speed
No they can't (unless one just finished climbing a mountain and the other is riding on a flat stretch of land, which would get rid of "etc"). Fitness level is determined by heart rate (as a percentage of max as Koffee said). If they have different heart rate, they're at different levels. Heart rate is a fairly accurate measure of effort. A higher HR means more effort which means lower fitness (all other things being equal).


For that ride, my SRM file says it was 1054 kJ or about 1000 Cal when you figure 22-25% efficiency
Where did you get the efficiency measurement from (i.e. what data)? If it drops to just 18% (a 4-7% margin of error on your efficiency assumption), my number is almost dead on. I thought powermeters were supposed to be more efficient than that. 25% is a terrible level of efficiency and I'd place little trust in anything that could not meaure 75% of my output. That's a staggering margin of error. You're saying nearly 3/4 of your energy was not measured. How can you trust those numbers? I don't have a powermeter, so I don't know if 25% is "good", but statistically, that would be meaningless data... Hardly worth ?$600? Surely it's higher than that. Or am I misunderstanding what you mean by "efficiency"?

One other thought about your SRM: if it's a rear hub model, it *only* measures power output by your legs and hips. It would not be a good measure of the work done (and calories burned) by your lungs, your heart, your digestive system, your upper body movements, holding the handle bars, etc. Remember, you burn calories just sleeping. Your power output on thaty ride was more than 1 MJ. You may have burned up to an additional 200-300 calories... Your SRM is a good machine, and I'd love to have one, but there are two measurements of physical effort available to the average person that are 100% accurate: heart rate and, to a lesser extent, breathing (which is really kind of tied to HR anyway).

My HR isn't 100% precise (for calculating calories), but since I know the error in whatever formula is used to calculate calories burned (and I wish I knew the formula so I could tweak it), I can calculate calories burned with a fair degree of accuracy...

PS in some studies (http://healthlink.mcw.edu/article/908757695.html is one) it has been found that a healthy person (in this study, one who weighs about 120-150), burn 100 Calories in 15-20 minutes at a 9mph rate. That's 300-400 in an hour *at a slow pace* for one of us...

Originally posted by CarlJStoneham
[B]No they can't (unless one just finished climbing a mountain and the other is riding on a flat stretch of land, which would get rid of "etc"). Fitness level is determined by heart rate (as a percentage of max as Koffee said). If they have different heart rate, they're at different levels. Heart rate is a fairly accurate measure of effort. A higher HR means more effort which means lower fitness (all other things being equal).

Heart rate ignores stroke volume which is half of the cardiac output equation and cardiac output is roughly proportional to the amount of work your body is doing. One of the main physiological adaptations to endurance training is increased stroke volume.

You could have a couch potato with a max HR of 180 riding at 175 and a pro with a max HR of 164 riding at 120 and the pro will be putting out more power and burning more calories.

HR as a % of max HR tells you nothing except how close a person is to his limit. It doesn't tell you how fit he is or how fast he is going.


Where did you get the efficiency measurement from (i.e. what data)? If it drops to just 18% (a 4-7% margin of error on your efficiency assumption), my number is almost dead on. I thought powermeters were supposed to be more efficient than that. 25% is a terrible level of efficiency and I'd place little trust in anything that could not meaure 75% of my output. That's a staggering margin of error. You're saying nearly 3/4 of your energy was not measured. How can you trust those numbers? I don't have a powermeter, so I don't know if 25% is "good", but statistically, that would be meaningless data... Hardly worth ?$600? Surely it's higher than that. Or am I misunderstanding what you mean by "efficiency"?

Yes, you are misunderstanding it big time. The bicycle is the most efficient human-powered machine with around 22-25% of food calories being converted to external work. The rest goes to keeping the body warm, various cellular processes, and other overhead.

To do this all by HR alone assumes that everyone produces the same amount of power at the same HR on top of assuming what efficiency the body converts food calories to work on the bike.

Originally posted by CarlJStoneham
One other thought about your SRM: if it's a rear hub model, it *only* measures power output by your legs and hips. It would not be a good measure of the work done (and calories burned) by your lungs, your heart, your digestive system, your upper body movements, holding the handle bars, etc. Remember, you burn calories just sleeping. Your power output on thaty ride was more than 1 MJ. You may have burned up to an additional 200-300 calories... Your SRM is a good machine, and I'd love to have one, but there are two measurements of physical effort available to the average person that are 100% accurate: heart rate and, to a lesser extent, breathing (which is really kind of tied to HR anyway).

The 22-25% figure is well-established and assume riders are not doing an upperbody workout while riding their bikes. I'm sure I expend some energy lifting my water bottle to my mouth but it's negligible.

Last year, I lost one pound for every 3500 kcal I expended while riding. Guess how many calories are in a pound of fat. This was consistent from spring to fall.


My HR isn't 100% precise (for calculating calories), but since I know the error in whatever formula is used to calculate calories burned (and I wish I knew the formula so I could tweak it), I can calculate calories burned with a fair degree of accuracy...


Sorry, but using HR to calculate calories burned is not accurate in any way, shape or form. With a powermeter it's off by maybe 5-10% but your way, it's several hundred percent. Your original numbers of 5,000 kcal for 3.5 hours is 1660 watts. Mario Cippollini can get close to 2,000W but for only a few seconds. Johan Museeuw can do around 800W for 3 minutes, if I remember correctly.


PS in some studies (http://healthlink.mcw.edu/article/908757695.html is one) it has been found that a healthy person (in this study, one who weighs about 120-150), burn 100 Calories in 15-20 minutes at a 9mph rate. That's 300-400 in an hour *at a slow pace* for one of us...

Well, it's way off and contrary to many other studies.

Your original numbers of 5,000 kcal for 3.5 hours is 1660 watts. Mario Cippollini can get close to 2,000W but for only a few seconds. Johan Museeuw can do around 800W for 3 minutes, if I remember correctly.

You're missing something in your equation, watts is a measure of power and only power. Unless you add time to it somewhere it doesn't mean anything.

Main Entry: watt
Pronunciation: 'wät
Function: noun
Etymology: James Watt died 1819
Date: 1882
: the absolute meter-kilogram-second unit of power equal to the work done at the rate of one joule per second or to the power produced by a current of one ampere across a potential difference of one volt : 1/746 horsepower

Are you saying he average 1660 watts for 3.5 hours?

Andrew

Your original numbers of 5,000 kcal for 3.5 hours is 1660 watts. Mario Cippollini can get close to 2,000W but for only a few seconds. Johan Museeuw can do around 800W for 3 minutes, if I remember correctly.
As I've said before, Squint, you can't convert Calories to watts. Watts is an instantaneous measurement of power. Calories are a measure of fuel. To hit 2000W, Cipollini probably only burns 10-20 Calories. You just can't convert that way (where do you get that you *can*?). Since you don't seem to understand this simple fact, your assertion that you can't use an HR to determine Calories burned is made weakened significantly (wrong in one area, wrong in another). Furthermore, if I was off by a "few hundred percent", I wouldn't've been able to peg your calories burned to within 25-35%, would I? Also, sounds like you're assuming more than one thing with your power meter , since you're *assuming* a certain level of upper body workout. Lance wouldn't assume the same thing since he tries very hard NOT to expend Calories & energy w/ upper body movement. You'd be surprised how many calories you burned on that ride that were NOT related to your leg/hip movement. Your Resting Metabolic Rate (the Calories required for "resting functions" (heart beat, etc)) can be as high as 75% of a person's Total Metabolic Rate. I'd estimate you burned a few hundred just breathing and doing involuntary stuff (heck, even your heart was burning calories just by pumping blood)...


Well, it's way off and contrary to many other studies.
I assume you'd be glad to provide some links to these other studies...? So far, I haven't found any online...

[QUOTE]Last year, I lost one pound for every 3500 kcal I expended while riding. Guess how many calories are in a pound of fat. [QUOTE]
How many pounds of muscle did you gain? Remember, as you exercise, you lose fat but gain muscle. Since muscle is denser than fat, your weight can actually go up. Furthermore, some of that might have been H20, though I assume you're not talking about weighing yourself before riding and then after for your "one pound for every 3500 kcal" (which would be almost ALL water).

:confused:

Power is work/time.
Watt=Joule/second

Look at your own definition! "one joule per second"

5,000 kcals/3.5 hours

That's energy (aka work) divided by time (hours).



Originally posted by Ajay213
You're missing something in your equation, watts is a measure of power and only power. Unless you add time to it somewhere it doesn't mean anything.

Main Entry: watt
Pronunciation: 'wät
Function: noun
Etymology: James Watt died 1819
Date: 1882
: the absolute meter-kilogram-second unit of power equal to the work done at the rate of one joule per second or to the power produced by a current of one ampere across a potential difference of one volt : 1/746 horsepower

Are you saying he average 1660 watts for 3.5 hours?

Andrew

What we're trying to communicate (and maybe not doing very well) is that watts is an "absolute" (i.e. instantaneous) measurement of power. For example, a 100-watt light bulb turned on for 1 second "uses" 100 watts. The same bulb turned on for 1 hour "uses" 100 watts. To measure the *quantity*, you have to speak of "watt-hours" etc. That's why the electric company always charges you for kilowatt-hours. If they charged you just by watts, you'd have a very low bill because it wouldn't matter that you had the lights on all month, since they'd only register as using 100 watts...

Now, if you're maintaining a steady wattage/hr, you can convert, etc. But to say that Johan can do 800w which means I can't do 1660 is meaningless. I didn't "do" 1660w. If you were to speak of watthours, you would have a more accurate representation. I'm not sure what all the formulae for that are (there are several), but it's not just a matter of converting watts to Calories and visa versa. Does your power meter display watts or joules or both?

What might also be helpful would be for you to post the formula(e) that you used for for your conversion. If you pay attention to units, I think you'll find they don't cancel correctly...

Watts is a measure of power which is work/time. To "convert" it to calories you need to know how long work at that rate was performed. This is very easy to figure out. Your average power multiplied by the duration of the ride is the amount of work you've done.

Has no one here taken physics in high school?

Your original numbers were way off, not your second guesstimate which wasn't as far off. The average calorie consumption for a Tour de France stage is 5,900 and you claim to have burned almost as many in 1-2 hours less time.

The Death Ride, which is around 140 mi and 15,000' of climbing and takes around 10 hours was just under 5000 kcal for a ~165 lb rider. And you ride 1/3 the time with probably less climbing and burn the same number of calories?

Actually, Lance and his coaches do make this assumption. Since they're well-versed in human performance, they know that it's been established that the efficiency of a man on a bike is around 23%. Lance and other well-coached athletes use their powermeters to gauge their training loads in kilojoules, not miles, hours, or average HR. In the offseason, he'll aim for fat loss of about 0.5 lbs/week. Any faster and he loses strength. To do this he carries a small digital scale and weighs the food he eats to estimate how many calories he eats everyday. He uses this data to maintain a caloric deficit of 1750 kcal/week which results in 1/2 lb of fat.

http://interactiveu.berkeley.edu:8000/CA/discuss/msgReader$662?mode=day&print-friendly=true

"During the cycling season, Armstrong calculates each watt he has burned on his bike and then uses a digital scale to weigh every morsel of food that passes his lips. This way, he knows exactly how many calories he needs to get through the day. When he is racing, his meals are gargantuan. (It took three men to lug the team's rations—boxes full of cereal, bread, yogurt, eggs, fruit, honey, chocolate spread, jam, peanut butter, and other snacks—into the hotel breakfast room during the Dauphiné.) On days when a race begins at noon or later, Armstrong will eat two heaping plates of pasta and perhaps a power bar three hours before the race, after having had a full breakfast."

http://www.dallastrigeeks.org/Races/IM_Brazil/KP/08-25-2003.html

"Stern: Energy Expenditure (EE) is related to power output, as EE = power x time. This is actually the mechanical energy used to drive the bike but is actually close enough to actual EE. The mechanical energy is actually in kj (kilojules), but can be converted to kcal (kilo calories) -- the more usual metric for nutrition.

Supposing, that a cyclist averaged 200 watts (W) for 3-hours, the mechanical energy (ME) would be: ME = power (/1000) x time (secs) = (200/1000) x (3 x 3600) = 0.2 x 10800 = 2160 kj

However, 1 kcal is equal to 4.18 kj, thus, 2160 kj is equal to 517 kcal. Obviously, this would be a very low EE for a 3-hr ride. Interestingly, efficiency during cycling is ~ 20 - 25% in trained riders, so these two figures approximately cancel, and we can then say that 2160 kj ride is approximately a 2160 kcal ride.

Efficiency (thermodynamic efficiency), is a measure of the actual mechanical work accomplished divided by the input of energy. This is mainly affected by cadence in cycling. Paradoxically, efficiency is *highest* at lower cadences, and lower at higher cadences. This is because energy is required to just move the legs (with example, no chain on the bike) and higher cadences require more energy. However, as power output increases, efficiency also increases. Therefore, topographical conditions have an effect on efficiency as you tend to pedal slower uphill and faster on the flat.

The biggest retarding force in cycling is air drag (hence the reason why we all try to get as aero as possible). If for example, you have two bikes a TT aero one, and a standard road bike, at the same speed under the same environmental and topographical conditions you'll need to produce less power on the TT bike than the road bike.

Heart rate can vary for a multitude of reasons, e.g., temperature, topographical conditions, humidity, fatigue, stress, caffeine, etc. Heart rate can vary quite dramatically even at a constant power output. As an example, when I complete 20-min TT intervals at the same power (ridden indoors on a trainer) my HR can vary by ~ 15 to 20 b/min depending on the session the day before, what I've done just before, fatigue, etc. Heart rate therefore becomes 'unreliable'.

Therefore, knowing power is the only realistic way of calculating energy expenditure, as trying to estimate it EE from e.g., HR is just too variable. Thus a HR monitor won't give an accurate or useable EE for cycling as there are too many variables not accounted for.

KP: Without the benefit of having a power meter, how can one asses their caloric expenditure while cycling (assuming they use an HRM)?

Stern: Basically, unless you want to do a reasonable amount of analysis it's pretty much impossible to estimate EE without a power meter, and get a meaningful answer."


P.S. I did make one mistake in my calculations but since you're all math whizzes here, I'll leave it to you as an exercise to find.

Hmmmm. I think I just figured out what you were saying when you compared me to Cipollini... Let me think this over


Your original numbers were way off, not your second guesstimate which wasn't as far off.
Gotcha

Ya know, Squint. You may be right. When I realized what you meant when you compared me to Cipollini, I realized you *were* talking about instantaneous watts. I ran the equations, and I got the following (units included):

That was a touch too small:

Is that what you were saying? I think I owe you an apology.

What software are you using to generate those equation-y images? MatLab? MathCAD?

The mistake I made was not multiplying your 5,000 kcal by 20-25% so the ~1660W needs to be divided roughly by 4 which comes out to close to 400W. Considering that a world cup race averages ~250W and that Lance himself might not be able to do 400W for 3.5 hours, your estimate is still too high.

I use MathType (I'm a math teacher and it helps for tests :) )

Yeah, I see what you're talking about on the wattage...