Margin of error on hrm watches

RachStevens06
RachStevens06 Posts: 10 Member
edited October 7 in Fitness and Exercise
i just purchased a hrm watch with calorie counting abilities. I wore it to class tonight. 1 hour of a class called 20/20/20, 40 minutes of high intensity (20 cardio and 20 strength training) and 20 minutes core work. Watch said I burned 759 calories. I don't know if I should believe that or not. Did 30 minutes of kickboxing right after and watch said burned 466 calories. I almost always try to ut in my max effort intommy workouts, just an FYI.
At the peak of my work out my HR was 181 (dammit those burpies are rough)
I just have a really hard time believing in 1 1/2 hours that I could burn 1225 calories. I'm not terribly out of shape and I'm not over weight or anything. My resting HR is 80 (in the 40%) but I want to make sure this watch isn't 'broken'.
So, sorry to ramble, is there a margin of error, a percentage, that a calorie counting watch can be off?
Thanks for any input you all can provide.

Replies

  • caroline_g
    caroline_g Posts: 201 Member
    There's isn't any set percentage or margin, no. Better watches will be closer to the mark, cheaper and worse made watches will be further from the mark. For things that are high intensity and a serious work out, that could well be correct. Try inputting it into MFP and see if they're a similar figure. Your kickboxing burn will be higher if you did it straight after an hour class anyway.
  • snookumss
    snookumss Posts: 1,451 Member
    You also need to SUBTRACT the calories you normally would have burned from those calories it shows you, so you aren't double counting calories.

    Example

    In ten minutes of watching tv I burn 15 calories. (calculated 1.5 per minute by dividing my total maintenance by the number of minutes in a day).

    If I do cardio for ten minutes and it shows I burned 100 calories, I have to subtract the fifteen I already normally burned, so I am not eating extra calories that are already counted!
  • dad106
    dad106 Posts: 4,868 Member
    You also need to SUBTRACT the calories you normally would have burned from those calories it shows you, so you aren't double counting calories.

    Example

    In ten minutes of watching tv I burn 15 calories. (calculated 1.5 per minute by dividing my total maintenance by the number of minutes in a day).

    If I do cardio for ten minutes and it shows I burned 100 calories, I have to subtract the fifteen I already normally burned, so I am not eating extra calories that are already counted!

    Actually you don't need to do this. You also figured it out wrong.. It's BMR, divided by 24, take that number then divide by 60 to figure out how many you burn a minute. Maintenance calories are you're BMR plus lifestyle... BMR is what you would burn if you laid in bed all day.

    Since everything though is an approximation anyway, it seems kind of silly to do this. I never did, and lost 29 pounds.. so I must be doing something right!

    To OP:
    When HRM's are used correctly(for steady state cardio and not weightlifting or laying on the couch to see how much you burn) and set up correctly(age, weight, height, gender, max heart rate and Vo2) they are about 80% accurate.

    http://www.myfitnesspal.com/topics/show/429688-new-hrm-how-to-make-the-calorie-estimate-more-accurate
  • Azdak
    Azdak Posts: 8,281 Member
    Depending on the brand, your setup, and how they are used, HRM calorie counts can be off by a significant amount--like 30%-100%. HRMs are not intelligent devices--they don't "measure" anything except heart rate. They estimate calories burned based on a number of assumptions and based on the setup information provided by the user. If any of those assumptions are not true, or if the setup information (e.g. your maximum heart rate, your aerobic fitness level) is inaccurate or not available, then the calorie numbers will be garbage as well. An HRM is just programmed to reflexively respond to the information it receives and spit out a number--it has no idea what is really going on.
  • RachStevens06
    RachStevens06 Posts: 10 Member
    Well, its a really cheap one :( Its the SportLine Solo 910. Next week when I take the class again I'm going to rate it against my friends Body Bugg she's letting me borrow. I would assume it's pretty off then.
    Thanks.
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