Watt Calculation

[SlickC2]

Greetings!

My first post so apologies if this has already been discussed. I'm curious about the calculation of watts expended. As I understand it, it is based entirely on the deceleration of the fan. Right...? Ok, if that is the case, I'm assuming other energy losses are minimal. I've seen for example a You Tube world record video where the machine feet are weighed down with massive lifting weights - why do that? Other videos show a "heavy weight" person barely moving the seat while frantically yanking with the arms and upper body - not a pretty sight!! Ok, so what I'm getting at is that there is significant energy losses in moving back and forth - experienced by us panting and sweating and building up body heat and melting all that built up fat reserves. Likewise the feet of the machine scraping on the floor - hence the need to weigh them down. So, I'm hoping someone can enlighten me!

All best

[PaulH]

The monitor reports the amount of energy (in Watts) put into the fan, so it's not trying to factor in any losses such as the movement of the entire erg, or your internal inefficiency. The calorie calculation that the monitor displays does try to allow for this, but quite crudely - it assumes that you use 300 calories per hour, plus whatever energy you put into the fan.

[SlickC2]

Thanks for the explanation. Presumably if you have a heart rate monitor hooked up, the calories from that could/should be used instead of a constant factor (would seem to make more sense to use a constant percent loss factor/function to me)? Even if it is, and likely to be some 800 calories/hr in my case, is it significant compared to what's put into the fan?

Cheers

[hjs]

Greetings!

My first post so apologies if this has already been discussed. I'm curious about the calculation of watts expended. As I understand it, it is based entirely on the deceleration of the fan. Right...? Ok, if that is the case, I'm assuming other energy losses are minimal. I've seen for example a You Tube world record video where the machine feet are weighed down with massive lifting weights - why do that? Other videos show a "heavy weight" person barely moving the seat while frantically yanking with the arms and upper body - not a pretty sight!! Ok, so what I'm getting at is that there is significant energy losses in moving back and forth - experienced by us panting and sweating and building up body heat and melting all that built up fat reserves. Likewise the feet of the machine scraping on the floor - hence the need to weigh them down. So, I'm hoping someone can enlighten me!

All best

Depending on the surface and how hard one erg, it does slide, during races the ergs are often taped to the ground. With sprints almost everybody gets a little moving around.

[PaulH]

Thanks for the explanation. Presumably if you have a heart rate monitor hooked up, the calories from that could/should be used instead of a constant factor (would seem to make more sense to use a constant percent loss factor/function to me)? Even if it is, and likely to be some 800 calories/hr in my case, is it significant compared to what's put into the fan?

Cheers

I'm not sure it would make more sense - the measurement at the fan is very accurate, so that should be used for the drive part of your effort, at which point how much of your heart rate should account for the recovery part? It's generally agreed that 300cal/hr is too high, but I don't think the HRM would be any more accurate given the approximations it has to make.

[SlickC2]

Ok, agree with all you say. I should rephrase my question to: How does one calculate the Total amount of energy expended during the exercise - all of which is coming from the rower. This includes the fan, the sliding erg, the sliding butt, the flexing legs, arms, upper body and all that huffing and puffing. i.e., Total Energy Loss = Fan + Erg + Human The Erg part is probably the easiest to deal with by taping or heavy weights or just bolting the thing down to a secure floor (otherwise you'd shake the house down!). The Fan part is we agree fairly accurately determined. That just leaves the messy Human part and some minor losses with the chain and bungee cord. It would seem to me that the heart monitor would be the best estimator of this rather than a fixed factor?

Best

[PaulH]

Perhaps in theory, but in practice I don't think so. Converting heart rate to energy use is already full of approximation, so it's really not that accurate (better than just saying "rowing uses 500 cal/hr", sure, but it still has a pretty big margin of error). And if you've already used the erg to measure the largest part of the effort (the drive), you're looking for precision in the 5% (or whatever) of the effort that's not part of the drive. I think any precision that you might be able to identify would be swamped by larger uncertainties.

Try laying out the calculation that you think would be needed, that might give us a better idea of what you're thinking.

[SlickC2]

Yes, I think I've climbed up the cactus pole on this one! Just reading the abstract of an article to clarify the confused thoughts: http://www.ncbi.nlm.nih.gov/pubmed/15292754

I think I understand now the issue with HRMs: they measure heart rate and VO2max as surrogates/indicators of actual (read Total) energy expended. The formula used depends on the form of exercise (cycling, rowing, running, ..) - presumably because different exercises involve different forms of energy loss in the body. Ok, that's clearer now. What I was thinking HRMs did was to calculate the energy loss incurred within the body (in burning up fat, sweating, heavy breathing, muscle flexing,...). Ok, my misunderstanding. I think I get it now. Sorry for the confusion on my part! I think I now understand why there are differing records for "light" and "heavy" rower categories.

All best

[SlickC2]

To summarise:

1. The C2 watt calculator based on the Fan calculates only the energy loss in spinning the fan regardless of any details of the human rower and how they are managing to spin the fan. The only assumption here seems to be that the fan ‘s inertia is not being altered (by for example build up of gunk)?

2. Your heart rate monitor attempts to measure total energy expended based on heart rate, VO2max, what type of exercise you’re doing, your age, weight and sex (and possibly height). I haven’t seen the Frankensteinish formula used for the calculation but I can imagine it must look an absolute mess! But, it may provide a baseline from which you can measure how you’re progressing. But, you won’t be able to use it to compare with others; well you can of course but the comparison may not be valid.

3. The C2 Watt measure does not give the Total Energy you expended during the exercise. It’s an underestimate. Does it matter? I suspect not if as PaulH says it amounts at most to 5% or so of the Total. It is supposed to be an independent, accurate and objective measure. But, if you want to test yourself against others (on watts expended), there are other factors that need to be considered in order to “level the playing field”; these being age, sex, weight, probably height as well. So, we’re back to the problems with the heart monitors in this case.

4. The heart rate monitor attempts to measure total energy expended. It is not accurate but it is more versatile if you establish baselines from which you can measure your progress (for each of the different forms of exercise).

5. Bottom Line: Be Happy; don’t kill yourself trying to match numbers with some other person as there are problems in making comparisons with others.

Best

[Bob S.]

To summarise:

1. The C2 watt calculator based on the Fan calculates only the energy loss in spinning the fan regardless of any details of the human rower and how they are managing to spin the fan. The only assumption here seems to be that the fan ‘s inertia is not being altered (by for example build up of gunk)?

2. Your heart rate monitor attempts to measure total energy expended based on heart rate, VO2max, what type of exercise you’re doing, your age, weight and sex (and possibly height). I haven’t seen the Frankensteinish formula used for the calculation but I can imagine it must look an absolute mess! But, it may provide a baseline from which you can measure how you’re progressing. But, you won’t be able to use it to compare with others; well you can of course but the comparison may not be valid.

3. The C2 Watt measure does not give the Total Energy you expended during the exercise. It’s an underestimate. Does it matter? I suspect not if as PaulH says it amounts at most to 5% or so of the Total. It is supposed to be an independent, accurate and objective measure. But, if you want to test yourself against others (on watts expended), there are other factors that need to be considered in order to “level the playing field”; these being age, sex, weight, probably height as well. So, we’re back to the problems with the heart monitors in this case.

4. The heart rate monitor attempts to measure total energy expended. It is not accurate but it is more versatile if you establish baselines from which you can measure your progress (for each of the different forms of exercise).

5. Bottom Line: Be Happy; don’t kill yourself trying to match numbers with some other person as there are problems in making comparisons with others.

Best

1. Build up of gunk on the cage is accounted for by the monitor. I am not sure whether or not the same is true of the fan, but I have never heard of it being a problem.

2. What heart rate monitor are you talking about. The C2 monitor just gives your the heart rate, nothing more. I assume that there are wrist monitors that can be connected to your computer to get other data, but that has nothing to do with the C2.

3. The C2 Calorie data is an attempt to estimate the total energy, at least in terms of fuel burned, but it assumes a sort of standard rower, stroke rate, and pace. It also takes into account that the average human is only about 25% efficient in converting fuel to work output. This means that the number of calories reported represent the total energy used to spin the fan and to account for other energy expended like accelerating your body up and down the slide - all multiplied by a factor of 4.

This tells it all:

Physics of rowing (ergometers):

http://www.atm.ox.ac.uk/rowing/physics/ergometer.html

Here is the pertinent section:

11. Power v. Indicated Calories

The Concept Model C also has a 'Calories' display as a (very) rough guide to how many calories an average individual has burned up in a piece. This is not the same as the mechanical work done.
Mechanical work W (a type of Energy) is defined as the average Power x time:

(11.1) W = P t

If Power P is measured in Watts and time t in seconds, then the Work W is obtained in Joules. So, rowing a steady 200W for 30 minutes, you would generate an amount of mechanical work

(11.2) W = 200 x 1800 = 360 000 J = 360 kJ

In physics, a 'calorie' is defined as the amount of heat energy required to raise the temperature of 1 gramme of water by 1 degree centigrade, giving 1 calorie = 4.2 Joules. Dieticians, on the other hand, use the term 'calories' differently - their 'calories' are 1000 times bigger ('kilo-calories', kC), so dividing 360 kJ by 4.2 gives the mechanical work done in terms of 'dietary calories': 85.6 kC

However, for the above workout you would actually get a displayed value approaching 500 kC, i.e. a factor 5 - 6 times larger. This is because the computer attempts to calculate the number of calories you burn up (effectively chemical energy contained in fats and carbohydrates) in order to generate the mechanical work. It uses the formula

(11.3) E = ( 4 W + 0.35 t ) / 4.2 [kC]

where E is the displayed number of calories [kC], W is the mechanical work in kJ, calculated according to Eq. (11.1), t is the time in seconds. This assumes that the body actually requires 4 units of chemical energy to generate 1 unit of mechanical energy (i.e. 25% efficiency) plus a background consumption of 0.35 kJ/sec (=300 kC/hour).

Comment Jon Williams of Concept2 (12 Aug 04)
The 300 kC/hour has always been our best approximation for keeping alive and awake and going through the rowing motion at a reasonable stroke rate on an erg with the flywheel removed. This was arrived at from internal experiments and observations, data from Fritz Hagerman and studies done at Ball State.
For the above workout this would give

(11.4) E = ( 4.0 x 360 + 0.35 x 1800 ) / 4.2 = 493 [kC]


The 'Calorie' output on a Concept ergometer is an approximate guide to calories [kC] burned rather than mechanical work performed

4. Same comment as 2.

Bob S.

[SlickC2]

Many thanks Bob for the definitive statement on the issue. Yes, I was referring to the Polar HRM which I use (just got the C2 Polar receiver today - nice to have the HR display on screen without having to stop and check).

Going through the calculations for the example row suggests:

1. The baseline energy expended by the body (300kC/hour) works out as contributing over 40% to the estimated total energy expended for the example problem. That's quite a bit more than I expected! So, just sliding along without pulling the handle will burn quite a few calories - no sweat! Must be something amiss here??

2. The mechanical work done is only 17% of the total energy expended! Wow, I hadn't realised how inefficient we are at using (chemical) energy!

3. The C2 calculator uses some "model" human for the calcs - average in all respects including sex. I'm having trouble visualising the half-man:half-woman bit! Ok, that means the calcs are even less accurate than the heart rate monitor (Polar, Garmin,...).

This turns the previous conclusions on its head. So now:

1. Body energy expended is much more than the work done on the fan.
2. The C2 calorie calculator is more cactus than those on the HRMs.

It would seem to me that C2 could use the same algorithms (or better) as those in the HRMs. Is there a reason for not doing so?

I must be missing something here....

Cheers

[TabbRows]

Just IMO...but all this fixation on calories expended, while interesting in theory, is essentially wasted effort. If you're trying to burn off that second PB&J sammie you ate at lunch, you're probably better off eating 1/3-1/2 your normal dinner than trying to fixate on exercise to do it for you. Weight loss belongs in the *** DELETE - SPAM *** (or at the refrigerator door), fitness belongs in the gym. Want to lose weigh? Cut back on portions and eat a more balanced diet with more fruits and veggies, less desserts and skip the prepackaged snacks. Want to get fit (cardio)? using watts and maybe HR, will give you a metric to gauge your progress during your exercise.

[Bob S.]

The C2 calculator uses some "model" human for the calcs - average in all respects including sex. I'm having trouble visualising the half-man:half-woman bit! Ok, that means the calcs are even less accurate than the heart rate monitor (Polar, Garmin,...).

Model was just my way of expressing it. They didn't use an average human and I did not intend to imply that. I think that it was something like a 180# man in relatively decent condition - what might be a typical erg user. Since a major part of the non-wheel-spinning energy expended goes into the acceleration of the body back and forth, the weight would be a significant factor. The heavier a rower is, the more energy lost in that way. Obviously stroke rate also comes into it. The higher the rate, the more energy lost. Effort (as measured by pace) is also a factor. If the rower is trying to get the maximum "distance" out of each stroke, there will be relatively more of the expended energy going into the wheel-spinning. At the same stroke rate, but with a light effort, the back and forth acceleration would still be the same, but the work measured by the monitor would be less. I think that C2 provides a weight correction for that calorie formula, but I am not sure. It would also be useful to have a rate correction.

Much too complicated to be of any use comparing different rowers, but probably OK for watching one's own progress. These are not the only factors. There is also the distance that the rower moves, varying body conformations like limb and torso lengths, the amount of leaning forward and layback....... Enough, already. The one thing that I get out of this is that heavier rowers would do well to stick to lower rates. Light weights can get away with higher rates, since they don't have to do as much unmeasured work. The work done on the wheel is the average force on the handle during the drive times the distance traveled by the handle during the drive times the rate. Those with short limbs and/or torsos with have shorter handle differences and will use higher stroke rates to make up for that. Some folks try to increase the length of handle travel by increasing the back swing with long reaches at the catch and long lay-backs. O†her gimmicks are going well past vertical shins at the catch and pulling the handle to the chin at the finish. These tricks give longer strokes , but are not efficient in putting force on the handle. The key in getting the most out of rowing is finding the best balance of force, length, and rate for each individual.

TabbRows has it right though. The calorie count is not very useful.

Bob S.

[SlickC2]

Ok, we hear you TabbRows but let's explain this "interesting" theory in lay terms:

1. You can lose weight by working out longer with less effort (smaller damper setting) than someone who works real hard for less time going after a world record.
2. Yes, the calorie counting by C2 or HRMs is not worth worrying about apart from being a progress indicator. What really matters is the heart rate zones you work out within and for how long.

I agree, that all the effort devoted to calorie counting calculators are not worth the effort, but knowing that a lot of the losses are within the body is, to me at least, a fairly important aspect of weight loss. Equally important is the fallacy of hard sweaty workouts being the only option to fitness.

Bob's exposition of all the confounding factors should put paid to any thoughts of getting a better calorie counter! In future I could imagine some sophisticated 3D scanner and a computerised C2 that can accurately calculate every aspect of one's workout to give you a constant stream of annoying coaching advice!

Cheers

[Bob S.]

I probably heard this one for the first time back in my high school days, over 70 years ago. "The best exercise for losing weight is pushing yourself away from the dinner table."

Bob S.