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  #11  
Unread 03-30-2011, 03:39 PM
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lylemcd lylemcd is offline
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I just looked for comparative data on ellipticals to other modes of exercise. Can't find much of anything which is a bit surprising.
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  #12  
Unread 04-01-2011, 09:32 AM
bigswole45 bigswole45 is offline
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I always wear my HRM to compare the two....usually they are about 20-30 cals off but never a huge difference. Also, I think the cardio machine also matters...machines like Lifestyle use the industry best (Polar) and from my experience they are pretty accurate.
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  #13  
Unread 04-01-2011, 10:14 AM
djc djc is offline
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Except your HRM can only calculate energy on the data it has, which is heart rate and maybe your age, weight and other user input information. Since the only thing that really changes from machine to machine is heart rate, its going to tell you that all machines are the same if you exercise at the same heart rate intensity.

There isn't much magic in the world, and all devices with a calorie readout can only make educated guesses based on the information they have. In order to calculate a number, HRMs probably just assume a MET for the activity you are doing that is a function of Heart Rate.

Maybe if you combined a HRM and a Bodybugg/GoWear Fit/Bodymedia Fit you might get a better number, but it is still just a guess. I believe Lyle has said that the GoWear Fits aren't particularly accurate for stationary bikes, since your arm really isn't participating in the exercise.
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  #14  
Unread 04-05-2011, 11:59 AM
Zé Apelido Zé Apelido is offline
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another method for approximating...

get on a stationary bike that has an accurate reading of power output (watts)

Watts = joules / second

4.184 kJ = 1 kCal

3600 seconds = 1 hr

# kCal / hr= Watts * 3600 seconds
4184 Joules

but this is calories as a measure of energy output (not input). In cycling, the efficiency between input and output is about 22% (varies maybe between 20-25% ?)

So calories burned in an hour:

kCal = 3600 * W / (4184 * efficiency)

assume 22% (.22)

kCal = 3.91* W.

now wear a heartrate monitor and plot at least a few steady state combinations of watts and heartrate, which you can convert into a relationship between heartrate and calories. then you could use your heartrate to estimate calories burned on other machines.

yes there are several assumptions involved but it will give a decent estimate
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  #15  
Unread 12-06-2011, 09:31 AM
CleanSnatch CleanSnatch is offline
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Quote:
Originally Posted by Zé Apelido View Post
another method for approximating...

get on a stationary bike that has an accurate reading of power output (watts)

Watts = joules / second

4.184 kJ = 1 kCal

3600 seconds = 1 hr

# kCal / hr= Watts * 3600 seconds
4184 Joules

but this is calories as a measure of energy output (not input). In cycling, the efficiency between input and output is about 22% (varies maybe between 20-25% ?)

So calories burned in an hour:

kCal = 3600 * W / (4184 * efficiency)

assume 22% (.22)

kCal = 3.91* W.

now wear a heartrate monitor and plot at least a few steady state combinations of watts and heartrate, which you can convert into a relationship between heartrate and calories. then you could use your heartrate to estimate calories burned on other machines.

yes there are several assumptions involved but it will give a decent estimate
None of these weight-heart rate-age-efficiency assumptions and correlations based on them are needed if these exercise equipment manufacturers would stop cutting corners and install a dynamometer and a tachometer. Measure the instantaneous torque and rpm and calculate instantaneous power = torque*rpm*2*pi/60. Add a timer and basic integrating circuit and you can have total mechanical energy (accurate to within 0.1% depending on the quality of the instrumentation).

Total biological energy expended will be higher because of
1. Frictional losses within the axle/gearings of the bike/elliptical (some of the biological energy expended has to overcome these frictional forces) and

2. Inefficiency within the human machine. Some of the biological energy expended does not go into moving the pedals but is expressed as waste heat, overcoming the inertia of the levers (limbs etc) and also the fitness of the person.

Last edited by CleanSnatch : 12-06-2011 at 09:54 AM.
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  #16  
Unread 12-06-2011, 01:03 PM
Zé Apelido Zé Apelido is offline
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Quote:
Originally Posted by CleanSnatch View Post
None of these weight-heart rate-age-efficiency assumptions and correlations based on them are needed if these exercise equipment manufacturers would stop cutting corners and install a dynamometer and a tachometer. Measure the instantaneous torque and rpm and calculate instantaneous power = torque*rpm*2*pi/60. Add a timer and basic integrating circuit and you can have total mechanical energy (accurate to within 0.1% depending on the quality of the instrumentation).

Total biological energy expended will be higher because of
1. Frictional losses within the axle/gearings of the bike/elliptical (some of the biological energy expended has to overcome these frictional forces) and

2. Inefficiency within the human machine. Some of the biological energy expended does not go into moving the pedals but is expressed as waste heat, overcoming the inertia of the levers (limbs etc) and also the fitness of the person.
Power output is going to be much different from human energy output. Gross mechanical efficiency of human movement is variable dependent on the exercise, but for cycling its around 22%. Stairclimbing perhaps a bit higher. For running, well you can't calculate power exactly, but can get some "effective power" curves that map energy to speed and grade (and bodyweight).

There is nothing wrong with using heartrate monitor as a general estimate of expenditure IF you've calibrated it to real power outputs, like I mentioned above.
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  #17  
Unread 12-06-2011, 01:17 PM
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lylemcd lylemcd is offline
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Quote:
Originally Posted by Zé Apelido View Post

There is nothing wrong with using heartrate monitor as a general estimate of expenditure IF you've calibrated it to real power outputs, like I mentioned above.
Why do you think that the hr/caloric expenditure measured in one mode will automatically transfer to another given differences in gross efficiency, training status, etc?
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  #18  
Unread 12-06-2011, 02:35 PM
Zé Apelido Zé Apelido is offline
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Quote:
Originally Posted by lylemcd View Post
Why do you think that the hr/caloric expenditure measured in one mode will automatically transfer to another given differences in gross efficiency, training status, etc?
Well the key term is "general". Keep in mind calories ~ VO2 consumption. Oxygen consumption is ~ proportional with cardiac output, which generally scales linearly with heart rate.

Yeah training status in general matters, but mostly that affects all exercise modalities. I agree that there could be some inter-exercise mode differences, but they aren't going to be major

quick google comes up with this paper, which people finds no differences in relationships for treadmill and elliptical.

I wouldn't be surprised if there's a difference with cycling...more isolated muscles used which could increase arterial resistance which can affect amount of cardiac output at a given heartrate.

Gross efficiency shouldn't really matter with the VO2 / heartrate relationship.

Pulling a number out of thin air, I'd guess there's a potential 5-10% error rate between modalities. And if you determine it via cycling, perhaps it will err on the underestimating side.
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  #19  
Unread 12-06-2011, 02:44 PM
Zé Apelido Zé Apelido is offline
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looking quickly at this study, I think there is a decent difference (maybe 5%) in the VO2 estimates between treadmill and cycling during initial training, then the difference decreases with time. these curves are scaled to % vo2max, which are lower in the cycling cases, so in absolute terms the initial differences may actually be less.
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