"Fitness trackers are largely inaccurate when counting calories, Stanford researchers say"

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  • dewd2
    dewd2 Posts: 2,445 Member
    The_Enginerd wrote: »
    dewd2 wrote: »
    I wear a Garmin Vivo Move. It counts steps. That's it. Nothing else. Because I have my baseline setup accurately Garmin knows when I take more steps that normal and adds those calories to my daily allowance.

    When I run I use a Garmin Forerunner. Since running can be reasonably measured (distance and mass) it knows how many calories I burn and adds them to MFP.

    You would think this is the case, but Garmin is always way high unless it has my HR data to use instead. Likewise with Strava, although Strava ignores HR in it's calorie calculations anyway so it's always off even with HR data available. It almost seems as though they are spitting out gross calorie burns instead of net or using an optimistic factor in the calculations.

    The formula: 0.63 * Miles run * Weigh in lbs = Net Calories Burned has worked well for me for years, and it is fairly consistent with Garmin's numbers when I wear my HRM. Garmin's calculation match on average, although since they are HR based, they are inconsistent due to effects of weather on HR. I always gets a high number when it's warm, or lower when it's cool/dark.

    Since I almost always wear my HRM when I run I haven't really tested it without. Maybe I can do some testing next after my race this weekend. I did have to adjust the settings a couple times to get it right when I first switched to Garmin. After that it has been very accurate.
  • dewd2
    dewd2 Posts: 2,445 Member
    edited May 2017
    So I managed to find a run without my HRM and compared it to a similar length run with it. My weight was within 3 oz for each run. Last October I ran 6.51 miles in 51:14. My HRM was dead or I forgot it (there's no data). My calorie burn was 731. In February of this year I ran 6.47 miles in 1:01:53. Garmin said I burned 829 calories for that one. So it gave me more calories for a shorter, less intense run with the HRM on.

    Bottom line, don't trust it. Figure out what works for you by trial and error and stick with it. Since I am able to maintain my weight (or lose if I want) while eating nearly all of my calories back I'd have to guess the Garmin with the HRM is more accurate. This kinda makes sense since they also include my VO2max in the equation (using the now defunct First Beat data). I'm guessing something like a normal activity tracker will not even allow you to enter your VO2max (assuming a non athlete would know or even care).

    Here's an interesting (but old) article from DC Rainmaker on Garmin's calculations.

    https://www.dcrainmaker.com/2010/11/how-calorie-measurement-works-on-garmin.html

    EDIT: Correction above. The newer HRMs use FirstBeat, not New Leaf. Too damned confusing...

    One more edit: FirstBeat doesn't care about the VO2max at all. But it does need an accurate HRM so most wrist models would not be sufficient (maybe none since it is based on time between heart beats or something like that... ).
  • MaddieZieglerFan25
    MaddieZieglerFan25 Posts: 8 Member
    I always subtract 200 calories from whatever Google Fit says I burned, and sometimes eat those calories back if I feel like it. I figure assuming a tracker is off by 200 calories is a good margin of error.
  • Tacklewasher
    Tacklewasher Posts: 7,122 Member
    DC did a decent review of the study. Points out where they went wrong in their methods. He doesn't disagree with the findings so much as how they got there.

    https://www.dcrainmaker.com/2017/06/thoughts-on-the-wearables-studies-including-the-stanford-wearables-study.html
  • MelanieCN77
    MelanieCN77 Posts: 4,047 Member
    Trackers are tools that provide data to work with, we shouldn't be slavishly responsible to exactly what they say. I see that as a similar mindset of following a "fad" diet, where people want to leave the intellectual heavy lifting to someone else. My AW cals are a little overestimated, my Fitbit cals are a lot overestimated. Knowing that I adjust my habits and behaviour, and still find immense value in the data and the records. You can build up an understanding over time with their assistance, but you have to police yourself and be sensible and honest with yourself, too.

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