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How calorie measurement works on Garmin fitness devices


Jaco Steyn
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So is my power read in this order of preference depending what is picked up?

1) HRM

2) Power meter

3) Speed and distance

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So is my power read in this order of preference depending what is picked up?

2) Power meter

3) Speed and distance

My Edge 705 actually has two different data fields. One is is called 'Cal' and is the calorie number calculated using speed and distance. The other is called 'Power kJ' and is the work value calculated from my power meter.

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My Edge 705 actually has two different data fields. One is is called 'Cal' and is the calorie number calculated using speed and distance. The other is called 'Power kJ' and is the work value calculated from my power meter.

 

Ok, I see it, I have set it up and will try it out.

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That is a great explanation on how they work but the other side of the argument is that it is all based on averages and is never going to be 100% accurate

 

These calculations are at best a thumbsuck & average. There are too many variables between one athlete and another for this calculation to be accurate. Max HR, age, fitness level, VO2max, metabolism, intensity of excersise, resistance, BMI, bodyfat... to name a few, needs to be accounted for to be accurate.

 

Plus you continue to burn calories after your session has ended, your cycling computer doenst account for that.

 

Basically, you need to be hooked up to machines in a lab with guys with white coats than can even tell the rate at which O2 mixes with your blood, for it to be more accurate.

 

But if you look at the different calculation methods between the Garmin 305/705 range and the 500/800 range, the latter seems to be closer to accurate than the duration based calculation of the 305/705 range

Edited by Tankman
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That is a great explanation on how they work but the other side of the argument is that it is all based on averages and is never going to be 100% accurate

 

These calculations are at best a thumbsuck & average. There are too many variables between one athlete and another for this calculation to be accurate. Max HR, age, fitness level, VO2max, metabolism, intensity of excersise, resistance, BMI, bodyfat... to name a few, needs to be accounted for to be accurate.

These algorithms don't really need to be 100% accurate. So long as they're fairly consistent and not massively inaccurate (e.g. the Edge 705 calculation can be out by 100%) they provide a good indicator for calorie tracking.

 

Although there are many variables, some of the algorithms account for quite a few, such as the New Leaf one that uses and approximation of VO2max. Even without accounting for all of these, the accuracy of the First Beat algorithm given by DCR is about 10%, which I would consider to be pretty good for calorie tracking purposes.

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Yup, with the 305/705 you can switch the unit on, leave it on your desk for 3 hours and you will see the calorie counter climb :blink:

 

"approximation" of VO2 max is the key word.

 

Take two athletes of the same age and weight and use the old 220 less age to get max HR (thats all you enter into your computer right?)

 

The might have the same age, weight, and max HR but their BMI, VO2max, fitness level, metabolic rates, etc will differ, how is the computer going to know this?

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"approximation" of VO2 max is the key word.

It does, however, seem that the approximation is pretty good. The First Beat algorithm (Edge 500, 800 etc) uses age, weight, height and activity level as inputs. It then estimates VO2max based on heart rate variability, amongst other things. This allows it estimate calories to within 7-10% of the values obtained from direct calorimetric measurements. It is also able to adapt itself as you get fitter. It's an approximation, but a pretty good one nonetheless.

 

Their white paper on the algorithm is pretty interesting:

https://sites.google...?attredirects=0

Edited by Edman
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