In academia calorie burn gets measured about the produced heat in a closed system. How accurate is the Fitbit Charge 2 when compared against that gold standard?

  • The problem with the calorie burn trackers is that they are only good at tracking calories for joggers or bikers on pretty flat terrain. And when I say good I mean somewhat adequate. Within a few years someone will make one where you can use special inputs for the activities you don't trust your watch with - being on a real stair stepper for instance. I could wear a tracker and it shows 300 calories and the machine shows 1000... You have to understand how a body burns calories - vertically more than horizontally - and what things improve metabolism to lose weight long term. – blankip Jan 10 '17 at 20:53

The calorie burn estimates that Fitbit provides takes into account the person's basal metabolic rate based on gender, age, height, and weight as well as the step activity recorded and any activities they log manually.

My impression is that the calorie burn reported by Fitbit trackers is really just a ballpark estimate and those in the Fitbit community often question the accuracy and consistency of the calculations. An article in Medicine & Science in Sports & Exercise stated that a study by Ball State University in Muncie, Indiana showed Fitbit and other trackers were highly inaccurate regarding calories to burn especially on non-step based activity, as much as 50% off.

  • 4
    Could you reference the university study in question? – Christian Jan 9 '17 at 7:59
  • I will preface this with the fact I actually love Fitbit trackers despite the inaccuracies. The study was done by Ball State University in Muncie, Indiana. From pubmed, ncbi.nlm.nih.gov/m/pubmed/27015387 – Marcy Jan 9 '17 at 17:42
  • Anecdotally, when I used my FitBit Flex and tracked both my activities and my caloric intake, my weight loss paced very closely to my expected weight loss given a 3000kcal net burn = 1 lb lost ratio. – LegendaryDude Jan 9 '17 at 18:57

To me, this seems close to being an X-Y question. The medical professionals (and to some extent the laboratory equipment manufacturers) are pushing back against these low-cost, continuous measurment sensors, because they're not accurate - but failing to appreciate that there are probably other gains to be made from replacing high precision with high volume data (both in time, and across populations).

In common with lots of embedded applications, the Fitbit doesn't measure calorie burn directly. What it does it take some more tractable measurements and user data to provide an estimate based on identified modes of activity (for example -sleeping, jogging, walking). Across a group of individuals, there is potential for significant variation between the observed parameters and actual calorie burn.

Where the data can be expected to be more accurate is in comparing relative calorie burn with different days for a specific individual, and the obvious advantage is the trivial instrumentation overhead compared with attempting any precision calorimitry in an open-air activity.

Its important to appreciate that the calorie number is an estimate, but when does anyone care about anything precise with calories? Even with blood pressure, the value is being able to identify changes over time in the majority of even medically monitored applications (rather than one-off diagnostic measurements).

Some effort does need to be made to formalise the value of herd measurements like this, educate professionals to work with low quality data, and educate users to appreciate this cheap data is not always individually informative.

  • If you want to lose weight you might have the option between two different kinds of exercise. Either you do 30 minutes exercise A and your device tells you it burns 600 calories or you do 30 minutes exercise B and it tells you it burns 800 hours. It's worthwhile to know whether you can trust the device to accurately tell you that one exercise burns more calories than the other. – Christian Jan 10 '17 at 11:42
  • OK, so these are your best estimates. Nothing else will give you any better estimate unless you're a professional athelete, or taking part in a clinical trial. The challenge is adapting to using new information that has poorly defined precision. In the round, many other factors will influence which mix of A and B is more effective long term for any individual. – Sean Houlihane Jan 10 '17 at 11:54
  • There are different heuristics for choosing an exercise than trusting a Fitbit. Whether or not it makes sense to trust the Fitbit to inform the decision with it depends on the data quality. – Christian Jan 10 '17 at 11:57

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