How are active calories calculated?

Discussion in 'Apple Watch' started by Seattleite, Aug 22, 2015.

  1. Seattleite macrumors member


    Jul 11, 2010
    I would like to know what method is used to calculate active calories burned. Previous to my Apple watch, I used a Mio Alpha heart rate monitor along with various fitness apps. Most of the apps reported similar calories burned based on heart rate. I have never gotten an accurate reading from my watch, regardless of what type of activity I am doing. And yes, I do understand the difference between gross and net calories. The Health app is calculating well below what it should for net calories. I have also made sure the heart rate monitor on the watch is getting similar readings to my Mio.

    For example, this morning I worked out on the elliptical machine for 51 minutes 42 seconds. I am 54 years old, 5'3 and 144 lbs. My average heart rate for the duration was 146 BPM. The elliptical machine read 546 calories when I was done (I know that is not correct). According to the Health app, I burned 238.59 calories. There is no way that is accurate for a fairly intense workout lasting over 50 minutes. When I go online and look at scientific studies and the calculators used, my gross calories burned should have been ~ 502 calories, and the net calories burned should have been ~ 450 calories. That is a huge difference from what the app is reporting. I am extremely disappointed in how the Health app is performing.
  2. mcaswell macrumors regular

    Dec 22, 2013
    I've observed over the years that when people get a new workout-monitoring device and it calculates lower calories burned than their previous device, they get very upset and assume that the old device has to be correct (and of course, in all fairness, heartrate-based calorie calculation is largely a guess).

    That said, your result sure does sound low. FWIW, a 40 minute bike ride yesterday, at a fairly relaxed pace (avg. 13.2mph) and with less exertion than your elliptical workout (avg. 131bpm) yielded a calorie calculation of 276 (active). This was maybe around 50 calories lower than what my Garmin Edge 500 said, so close enough I suppose.

    But again, my ride, shorter and with apparently less effort (though I don't know if comparing two peoples' BPMs is an accurate indicator... I'm about 10 years younger, but a bit taller and heavier) showed higher calories. I wonder if Apple is using speed/distance for a cycling activity to supplement heart rate in the calculation, something that is not available on a stationary machine (I'm assuming there's no way to link up the machine with the AW to give speed info).
  3. BlueMoon63 macrumors 68020

    Mar 30, 2015
    Which workout app choice did you choose? The numbers you gave are way too low no matter what choice you chose.

    Once you completed the workout and opened the activity app on your iPhone, it should show your workout just below your stand hours. If you click on it, it should show your workout and average heart rate.

    Also, make sure you have entered your personal information on the Apple Watch app on your phone under health. It will want to know your age, sex, weight and height.

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  4. parseckadet macrumors 65816


    Dec 13, 2010
    Denver, CO
    That does sound very low. Are you making sure to select the elliptical workout? The machine I always use has options for entering your age and weight, and while not the same, my watch is usually in the same ballpark as the total indicated by the machine (usually a little less, which I assume is because I'm 6'3" and the machine is assuming average height).
  5. fmjordan1957 macrumors newbie


    Aug 24, 2015
    I would assume that the formula for the calculation is based upon age, gender, height, heartrate and weight but there is no way any device can project what any individual metabolism might be. Two individuals with identical components listed above can have different metabolic rates and therefore provide different results. Let's face it, if you want exact calculations you will need to go to a doctors office and perform a stress test....aside from that the watch gives you enough information.
  6. BlueMoon63 macrumors 68020

    Mar 30, 2015
    You are correct for the formula and metabolic rate playing a key factor. Same as BMI readings taking no consideration for muscle mass as I am listed as obese 25BMI even though I am about 16. I am 6'4 225-230 and it says I should be closer to 205.

    I don't think the person ever came back to tell us if she even setup her age/weight/height/etc. No way the watch registers 200 + calories for that much of a workout. I would get that walking for 50 minutes and heart rate of 105.
  7. BarracksSi Suspended


    Jul 14, 2015
    My guess is it's counting time above a certain heart rate.

    I've had two recent walks along the same route, one with an average HR below 90, and the other just above. The first one with a lower HR (and easier pace) didn't fully register as "exercise", but most of the second walk did.
  8. BlueMoon63 macrumors 68020

    Mar 30, 2015
    Yea - I think she said that her heart rate was 146 for the entire workout and that is what I was using to say it must be something wrong. I wonder if the defaults are still in play here. Not even sure what those would be.

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