back to article Don't rely on fitness trackers to track number of calories burned

Your fitness tracker might measure a heart rate accurately, but not the amount of calories burned, according to a study published in the Journal of Personalised Medicine. “The heart rate measurements performed far better than we expected,” said Ashley, “but the energy expenditure measures were way off the mark. The magnitude …

  1. Sampler

    Do people really do that?

    I mean, if you're stupid enough to think the cheap plastic on your arm is as good as a lab in terms of accuracy and you use it to say "I've walked five km so I can now have a doughnut" then I'm guessing you're going to have a lot more problems in life then a few extra calories..(such as what to do with your collection of bridges)..

    Precision in these devices is not needed, they're to show trends to promote action - oh, I've not had enough steps today, I should go for a walk.

    There should be a body that independently verifies these things, just so consumers know at least the level of inaccuracy to go with - I also question how many devices were used from a provider in case they got the one made on a friday arvo.

    1. Anonymous Coward
      Anonymous Coward

      Re: to think the cheap plastic on your arm is as good as a lab

      I shouldn't think they do expect it to be as good as a lab. But it would not be unreasonable to believe (or perhaps hope) that the devices, given the marketing, get within 10% or so of an accurate figure, so they can at least be used as a general guide for how you are doing.

      1. Anonymous Coward
        Anonymous Coward

        Re: to think the cheap plastic on your arm is as good as a lab

        And if they're only accurate to, say, one significant figure, then perhaps they oughtn't create a misleading impression by displaying 3 or 4 significant figures of precision.

        1. Anonymous Coward
          Anonymous Coward

          Re: to think the cheap plastic on your arm is as good as a lab

          Isn't the point that they consistently over-measure because they don't take certain factors into account. At least that's how I read the article.

          In the end two people with the same BMI can still gain weight at different rates for the same calorie intake. Therefore it doesn't matter too much if the figure from your watch/smart-phone app is wrong as long as it varies in proportion to effort expended. If 10K steps a day sees me gain a kilo a month then I need to eat less or walk more.

          1. DocJames
            Coat

            Re: to think the cheap plastic on your arm is as good as a lab

            In the end two people with the same BMI can still gain weight at different rates for the same calorie intake.

            Bzzzt. False. Unless expending different amounts of energy.

            At least, in labs when calorie intake and output is rigorously controlled. Not so much in studies when calorie intake is self reported and exercise is unmeasured - which sadly seems to be the 'scientific' standard.

            But I agree with the rest of your comment. My white coat, thanks.

    2. John Brown (no body) Silver badge

      Re: Do people really do that?

      "There should be a body that independently verifies these things,"

      "Results shown are for entertainment purposes only. No medical or other claims are made".

      There ya go, fixed that problem. Next!

    3. big_D Silver badge

      Re: Do people really do that?

      I have had a couple of FitBits and they aren't that accurate.

      I can stand up, go through the house, up the stairs, clean my teeth, walk to my bedroom... At it registers either 200 steps or 0 steps...

      On the other hand, chopping up vegetables can be worth a thousand steps.

      Scratching my stomach? That is also a few steps.

      I was very surprised, when it registered that I went for a bicycle ride at 11pm at night, when I was in bed...

      The things are okay as a motivation, but the readings need to be taken with a bit of salt.

  2. Palpy

    Yes, of course somebody --

    -- should verify such claims. Should. But it's not the purview of the FDA, certainly, and I'm not sure what body would tackle the vast amount of dodgy tat for which extravagant and misleading claims are made.

    Unless the consumer does it.

    On the bright side, I'm very pleased that most of the heart rate monitors showed within 5% of actual heart rate. Last time I checked (a few years ago) only the chest-strap heart monitors were accurate.

  3. Anonymous Coward
    Anonymous Coward

    IoT - Just about what was to be expected...

    They're better at slurping location data and other stuff for tracking and monetizing purposes. So hey good news for marketers everywhere...

  4. Anonymous Coward
    Anonymous Coward

    If you just said 2500 calories every day, it would not be off by 93%.

    1. Flocke Kroes Silver badge

      Only off by a factor of 1000

      2500 kilocalories per day is a sensible guess at the required intake for an unknown human. You can add extra confusion with 1 Calorie = 1000 calories even though Mr Calorie did not invent the kcal. I see food manufacturers getting this wrong all the time. It is almost as if they want me to believe my usual 2km row is worth 700 doughnuts, not 0.7.

      1. Nick Ryan Silver badge

        Re: Only off by a factor of 1000

        The calorie thing by way of food intake is laughably inaccurate anyway. This doesn't mean that it doesn't have value, because some measure is better than no measure, just that people shouldn't accept it as utterly accurate.

        Consider this: how does a human body process food? The chewing, saliva and other enzymes are just the start of the variables, then there's the bacteria in the digestive system and their variety efficiency, which greatly varies depending on the bacterial make up, the pre-processing of the food (cooking, chewing, etc), the food itself and the internal conditions at the time (food bulk, temperative, acidity, etc). Basically, it's complicated. Very complicated. Also, some foods require considerably more energy to break down than others - this is generally the value of more natural foods compared to heavily refined foods which are usually very easy and quick to break down, as in the difference between long chain "sugars" and short chain (refined) "sugars".

        How do we measure the calorific value of food? The original method was through measuring the temperature change in water through burning the food. The methodology these days is a bit more refined than this however the overall process is/was based on this. The calorific value of most modern foods are calculated using pre-set values and the manufacturer's estimated/average measure of the food components and extrapolating from there.

  5. J.Smith
    Happy

    I'm done for the day, my fitbit shows me I burnt 1546 calories, all I did was go upstairs to the loo. I'll be a fit bit in no time!

    1. m0rt Silver badge

      "I burnt 1546 calories, all I did was go upstairs to the loo"

      "You do NOT want to go in THERE! Phew"

    2. Roopee
      Joke

      "I burnt 1546 calories, all I did was go upstairs to the loo"

      Did it also show how much weight you lost?

    3. web_bod
      Paris Hilton

      I hope you washed your hands and cleared your browser history

  6. Anonymous Coward
    Anonymous Coward

    Exercise

    What is this exercise you speak of?

  7. DougS Silver badge

    Not sure how they can ever measure calories accurately

    The gold standard involves a breathing mask to capture your CO2 metabolization, which would be an inconvenient way to wear a watch.

    Unless there's a proxy that can be measured via trace gases coming through the skin, all you'll ever be able to do is estimate based on heart rate. Perhaps the accuracy of that might be improved if you had it calibrated via a proper measurement, because a HR of 100 indicates a different amount of calories burned for a fit person vs a fat person, but if it was calibrated that when you have a HR of 70 you are burning X, a HR of 120 is burning Y and a HR of 170 is burning Z, your now-calibrated watch should be a lot more accurate (if still not perfect)

    1. Roopee

      Re: Not sure how they can ever measure calories accurately

      Heart rate is clearly not a proxy for calories burnt - just think of all the other reasons your heart rate can soar, that don't involve much if any effort on your part...

    2. Cuddles Silver badge

      Re: Not sure how they can ever measure calories accurately

      "Unless there's a proxy that can be measured via trace gases coming through the skin, all you'll ever be able to do is estimate based on heart rate."

      To be fair, you can estimate based on a few more things than that - age, gender, weight, cadence, speed and altitude tracking, and maybe other things as well. It's still just an estimate, and one that needs additional equipment with proper calibration to even manage that, and it can still be thrown way off by environmental factors such as wind and rain, but you can do a lot better than just slapping on a watch with a not-too-terribly-inaccurate heartrate monitor and hoping it will tell you something useful. The main problem is that most people aren't actually interested in fitness and simply want to slap on a watch and have it tell them they're awesome for occasionally using their legs, and all these fitness trackers and "smart" watches are more than good enough for that.

  8. wiggers

    If you're counting calories you're doing it wrong. Lose weight in the kitchen, gain health in the gym. #ketogenic

  9. Commswonk Silver badge

    "Don't rely on fitness trackers to track number of calories burned"

    Not least because their true purpose in life is to part the gullible from their money.

    As is the case with a lot of other (i.e. most) shiny stuff...

    1. Anonymous Coward
      Anonymous Coward

      Re: "Don't rely on fitness trackers to track number of calories burned"

      I like my fitbit. Do I think it's accurate? Of course not. I'd need to be towing around a laboratory for it to accurately do the stuff it claims to do (which would probably increase my calorific output). But, if I want something that gives me a general idea of how active I've been in a day or week, why not have a fitbit / other similar stuff. I like it, it works for me. Just cos you don't agree I don't think it necessarily makes me gullible. But thanks for patronising me on this beautiful Friday, it's appreciated.

    2. Fading Silver badge
      Holmes

      Re: "Don't rely on fitness trackers to track number of calories burned"

      I use mine (Fitbit Charge HR) to reduce the excess on my private medical care. Oh and tell me when my phone is ringing (on silent) and for finding out the time.

  10. defiler Silver badge

    DAMMIT!!

    How can I sate my consumerism whilst making a token gesture to shedding flab now??

    1. Commswonk Silver badge

      Re: DAMMIT!!

      Try jogging to the Pizza Emporium instead of pressing buttons on your smartphone.

  11. werdsmith Silver badge

    These things are about targets, trends, motivation and comparing one day to another.

    I doubt that anyone believes they are showing a precise measure of energy use, and what would anyone do with a precise number anyway?

    Stanford Prof unnecessary, just simple thinking for 5 seconds will tell us the same thing.

    1. Tinslave_the_Barelegged Silver badge

      > These things are about targets, trends, motivation and comparing one day to another.

      I wouldn't have one of these anywhere near me, but observationally the main use seems to be one-upmanship against the next data subject wearing a similar device, so just a variation of the last aspect of the statement seems to be a significant factor. As such, these warnings of inaccuracy are probably appropriate, as people could be basing their "targets, trends and motivations" against metrics that may not be as healthy as expected.

      It's easy to see a market for such devices, but gosh, in the modern context, it's hard to see any valid overall good of a mass market in them.

  12. Chemist

    If you'd like a (rough) algorithmn ...

    from one who's struggled with weight over many years but succeeded in the end.

    If you weight ~85kg ( otherwise scale it)

    1 mile walking is 100 Cal ( almost any speed of walking)

    1 mile running is 130 Cal

    100 metres ascent & descent is 100 Cal All figures approx. and sorry to mix units but they are easy to remember.

    So doing the ~12 mile round trip from (say) Zermatt (1600m) to Gornergrat (3100m) would be approx. 1200 Cals for the distance +1500 Cals for the height = ~2700 Cals or ~~ 2/3rd of a marathon.

    The figures are accurate enough to give you some idea of the amount of effort needed to burn off all those goodies.

    Other exercise is available but I don't have such well-used values.

    1. DocJames

      Re: If you'd like a (rough) algorithmn ...

      Despite the misspelling of algorithm, I wish to give chemist many upvotes.

      Remembering how many calories are achieved through exercise, and how many are contained in 'snacks', makes it very clear how to lose weight.

  13. Anonymous Coward
    Anonymous Coward

    Well I found them useful

    Do I think they're very accurate? Nope. Are they accurate enough? In my case yes. The FitBit surge (my weapon of choice) tracks pulse, altitude change, GPS and general movement combined with data I have entered such as age, gender, weight, height.

    Simply by aiming for 1000 calorie intake less than the tracker said I'd expended, I lost 3 stone in as many months. I'm now at a happy weight so aiming to keep calories in roughly the same as my FitBit says are going out.

    Of course, my 1000 calorie deficit may only have really been 500 or maybe even 1500. Without a lab, I don't know but it is good enough. Ultimately it can't lose weight for me or get me fit, I did that by moving my fat arse more and eating less - aided by data provided by this gadget.

    I know many fat bastards who have worn these things for years and are no slimmer/fitter, they're in denial and think they can eat as much as they want because their watch beeps and vibrates when they've waddled 10,000 steps.

  14. Anonymous Coward
    Anonymous Coward

    vanity calorie burning

    If "vanity sizing" is purported to sell certain brands of women's clothes, might excessive calorie burn rates be the equivalent fitness tracker sales tactic?

  15. mrvvg

    Comments have brightened up an otherwise dull morning. If you don't measure it, you can't measure changes in lifestyle and from my experience I needed a bit of encouragement. So my fitbit transponder lives in my pocket, not on my wrist - so the accelerometer cannot measure chopping carrots. But does show me how much or little I have moved in my sedentary job..and for how long. We aren't designed to sit all day.

    It ONLY has ANY value if you watch what you eat - not necessarily calorie counting, just sensible eating, AND NO SNACKS, deep fried Mars bars or other culinary delights that are heart attacks on a plate.

    I have never bothered taking a scrap of notice of the 'calories burned', and the Chemists rough counter is much more use - two miles walking = 200cals, plus the height gained, plus a bit more for being 10kg heavier.

    Simples really, eat less, more healthily, more exercise, live longer.

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