Anyone who is just using the GWF and not trying to combine the data with SparkPeople, Polar, or anything else should just skip this rather long post
This is mainly for fit44 who I did not mean to confuse.
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To answer the question of where the numbers come from in detail, you might want to go onto the site and read the science articles they point to - that's what I did. Actually, I found a link to their medical products and that's wehre the articles were, come to think of it ... And, I'm no expert in the product - just a techie scientist who reads quite a bit and has been playing with gadgets for exercise measurements on a hobby-basis for some time now
But to answer your question, in probably far too much detail or far too little depending on your background … of course we all know that these devices don't actually measure the calories our bodies burn in a day. They are estimating calories burned based on input from their sensors. That's as true for the tanita daily metabolic rate calculation as it is for the polar HRM and for the GWF. If you read the scientific articles behind these gadgets, to see how they are developed, you'll usually discover that the developers took readings with people wearing/using the devices, and also estimated calories burned with a different, usually more precise or at least well-known device. Next, they'll often use some form of mathematical modelling. Neural networks are popular - I think that the Suunto uses that for EPOC in their HRM - and I recall reading others that use genetic algorithms or a combination. Curve fitting, etc. This is part of the design process.
Once you have a mathematical model and have validated that the readings from the sensors, when fed into that model, accurately match up with the results you are getting if you use that fancy and expensive/known medical device that’s only available in hospitals, the next step is to convert the math model into electronics and tie that to the sensors so that you can display the results in some way. You can do this by old fashioned low level circuit design, or by programming a modern computer chip, an EPROM/FPGA, or somewhere in between. It's here you get into some neat discussions about how to handle heat dissipation, cost of the chips, programmability, and so on. But the end result is that the circuits/electronics plus the sensors are being used to produce the calorie estimation. And the way that the circuitry is developed comes from having done experiments with a variety of sensor inputs, comparing them to "the real calorie burn" (as best you can comput it), and then coming up with a model that's embedded in your device. You also get some that don't compare calorie burn but use tables instead.
This still doesn’t tell you why it matters what your metabolic rate is, or weight, or anything like that. That comes from the calibration process I was talking about – developing the model that goes into the device. Take a look at sites like this one
http://www.freedieting.com/tools/calorie_calculator.htm#
Under the advanced options you will see that there are at least three different ways to estimate calories used on this site alone, and these depend on your inputs of anything from your actual muscle mass, body mass, etc etc etc. If you use a gadget that was developed, or calibrated, using one kind of estimate, you will get different numbers than if you use a gadget that was developed, or calibrated, using a different kind of estimate. You’ll also see the same thing if you use the different advanced options in those calorie meters. The more information that these devices use, the more (except in cases only mathemeticians would love) accurate they are. That includes more and better sensors, and more information about individual physical characteristics.
And now I have thoroughly bored everyone
- very sorry for that. You can tell when I get pedantic like this that I’m reverting back to my professorial days
The short story, if you are converting a single trip calorie count to SparkPeople/Polar HRM measurements, subtract one calorie per minute and then enter the data. Otherwise, just enjoy it all by itself
You can use the GWF just fine without worrying about any of this. I wouldn't have brought it up except that there may be a few people who are converting to the GWF from some other device, and in those cases, they might not be aware that there are differences in measurement styles that become important if you are working with a variety of websites and measurement devices. If I didn't make the conversion I mentioned in my email, subtracting out about one calorie a minute, I'd find myself over by 100-200 calories a day, which would likely result in a ten pound weight gain a year
I didn't want anyone who might have been influenced by my personal enthusiastic endorsement to end up like that.
Personally I think the best way to use any of these devices is to look at your results, and then either adjust your calorie intake or fitness goals up or down depending on whether you are happy or not.
