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Fitness Trackers Out of Step When Measuring Calories, Research Shows (theguardian.com)
Fitness devices can help monitor heart rate but are unreliable at keeping tabs on calories burned, research has revealed. From a report on The Guardian: Scientists put seven consumer devices through their paces, comparing their data with gold-standard laboratory measurements. "We were pleasantly surprised at how well the heart rate did -- under many circumstances for most of the devices, they actually did really quite well," said Euan Ashley, professor of cardiovascular medicine at Stanford University and co-author of the research. "At the same time we were unpleasantly surprised at how poor the calorie estimates were for the devices -- they were really all over the map." The team tested seven wrist-worn wearable devices -- the Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn, and Samsung Gear S2 -- with 31 women and 29 men each wearing multiple devices at a time while using treadmills to walk or run, cycling on exercise bikes or simply sitting.
There are too many variables involved in determining calories burned by any biological entity, and these 'fitness bands' are not the only device that has this problem, either. The closest you can come are devices that measure power generated by your muscles (PowerTap hubs, SRM or Quarq cranksets and other bicycle-mounted direct measuring instrumentation like them, rowing machines with an ergometer, etc), and even then there is a variable 'biological efficiency' term in the equation that means you can only call it an estimate. Some of the worst accuracy devices are things like the treadmills and stationary bikes in a public gym, which just use statistical averages of a range for calories burned given a level of exertion, and even then they tend towards the high end of the range to keep people motivated to continue using the treadmill or stationary bike. Something like these fitness bands work in a similar way, and I'd fully expect that they too tend to estimate on the high end of the range of 'calories burned' to keep you motivated. The fact that they track heart rate means it's a little more accurate, given one more term in the equation, and if they have a way to enter your bodyfat percentage, that would improve the estimation also. There are other factors you can plug into such an equation to make it more accurate, but in the end it's still just an estimate because of the efficiency factor. Therefore: none of what is being claimed here about it's lack of accuracy in 'calories burned' is terribly surprising. Of course for the average person, moving their body for significant amounts of time (not just getting off the couch, going to the 'fridge for another soda/beer, then back to the couch) is good regardless of trying to track 'calories burned', and to be quite honest, your dietary intake is more important when trying to lose excess bodyfat than exercise is. Of course you don't need any 'fitness bands' for that, just a decent pair of running shoes, so that doesn't make the company any money now does it?