Accuracy of HRM

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erinjohns315
erinjohns315 Posts: 6 Member
in Health and Weight Loss
I have a Timex digital heart rate monitor with a strap that I got a few years ago. I have been using it to calculate my calories burned, but yesterday I went for a bike ride with my kids and wore it just to see what it would say expecting it to be around 100 calories since I would be going slow. We rode for 45 minutes and my HRM said I burned 723 calories, which seems incredibly high to me considering the pace we were riding. I have reset the settings (weight, resting heart rate, etc). Is it possible that my results are much lower than what it says, or are HRM usually accurate?
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Replies

  • omma_to_3
    omma_to_3 Posts: 3,265 Member
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    HRMs are pretty accurate for steady state cardio. For anything else, less so. And by "pretty accurate" I mean generally within around 20%. It's the best estimation option we have. That said, I have heard the Timex greatly exaggerate the calories burned (the studies I've seen done on accuracy are typically done with Polars which are more accurate than many).

    And, for 45 minutes of slow biking, that number is astronomical.
  • jstout365
    jstout365 Posts: 1,686 Member
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    I also have a Timex and I think it gives high calorie burns as well. I did 70 min of Interval Training this weekend and averaged 165 BPM and it gave me 1134 for calories burned. I'm 5'2 and 138 lbs......I was soaked in sweat and know I worked hard, but burning 16.2 calories a minute average for non-static cardio is a bit ridiculous. I know I need to adjust my profile stats with the watch, but it has always given me super high readings.
  • cwolfman13
    cwolfman13 Posts: 41,867 Member
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    You did not burn 723 calories in 45 minutes of recreational bike riding. I burn about that with 20 miles or so on my bike...pace doesn't really matter so much, it's the distance that matters most and then pace and terrain will play a roll.

    Something is definitely amiss there...that's over 16 calories per minute which is pretty much impossible to do for any sustained period of time.
  • Vince_1964
    Vince_1964 Posts: 359 Member
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    I have a Timex HRM too. This morning it told me I had burned 1042 calories for a 60 cardio endurance workout (boot-camp type training - which is just over 17 cal/Min. I have always felt the calorie burn rates were too high/exxagerated on the Timex HRM, so I use 70% of the total from the HRM to estimate my actual burns for various workouts (today that was 729 cals ... 12.15/min).
  • erickirb
    erickirb Posts: 12,293 Member
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    My understanding is that Timex are a quite generous on the amount of cals burned that it tells you. It is very difficult, unless you are really heavy, to burn that many cals/minute over an extended duration. I would suggest you find an online calculator and just plug in the average HR from your Timex and use those cals burned. Livestrong has some good calculators to do this for you.
  • eddiesmith1
    eddiesmith1 Posts: 1,550 Member
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    Virtually no chance you got that burn cycling at a comfortable slow pace. In fact to get a proper read cycling you need a power meter and bike computer
    a better guess is about 250 calories for 45 minutes leisure cycling (I ride 14 km a day when I ride to work and as half is uphill and half downhill I just go with average speed for my weigh - and I burn about 550 based on my speed which would likely be much higher since it's not a leisure ride
  • doctorsookie
    doctorsookie Posts: 1,084 Member
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    well given your whole body is tense and working hard to stay on top of the bike and the slower you go the hard you have to work to stay balanced, I would say it is pretty good. Also, you said you redid the settings. Have you not used it in a while? Was it still set to when you were heavier? If so, it might have been calculating based on a higher weight and you would have burned more when heavier. :happy:
  • heybales
    heybales Posts: 18,842 Member
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    I had Timex - it's terribly inflated.

    Unless you rode up steep uphill, and had no downhill somehow, and you weigh a lot. But I doubt the kids would keep up - unless you meant you were towing the kids in trailer, up a hill, in to the wind, on a heavy bike.

    Even the best Polar's loaded with lab measured stat's can be off. And Polar pay's for some studies they use the formula's from. Other formula's they use studies already done.

    http://www.myfitnesspal.com/topics/show/459580-polar-hrm-calorie-burn-estimate-accuracy-study
  • lthames0810
    lthames0810 Posts: 722 Member
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    I have similarly overstated calorie burns from steady cardio with my Timex HRM.

    BUT, I use a Garmin cycling computer with a chest strap heart rate monitor (and personal data settings) and it gives me the same high reading. It gave me over 2000 calories burned from a one hour high intensity (zone 5) ride last week.

    I now take the average heart rate from the HRM and plug that into the calculators on shapesense.com.

    Edited to add: The reason I got a Timex was because Polar makes you send your device back to them (and wait several weeks) in order to replace the batteries and the Timex can be changed in a watch shop.
  • heybales
    heybales Posts: 18,842 Member
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    I have similarly overstated calorie burns from steady cardio with my Timex HRM.

    BUT, I use a Garmin cycling computer with a chest strap heart rate monitor (and personal data settings) and it gives me the same high reading. It gave me over 2000 calories burned from a one hour high intensity (zone 5) ride last week.

    I now take the average heart rate from the HRM and plug that into the calculators on shapesense.com.

    Which Garmin, because the older ones didn't use HR for getting calorie burns? Though they display it for training reasons.

    Some newer ones using Firstbeat algorithms can be better, but mainly with running.

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

    Because ya, 2000 cal / hr, or 33 cal/min, is off the charts for a sustained effort, unless you are a pro of course with massive VO2max.
  • omma_to_3
    omma_to_3 Posts: 3,265 Member
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    Edited to add: The reason I got a Timex was because Polar makes you send your device back to them (and wait several weeks) in order to replace the batteries and the Timex can be changed in a watch shop.

    This isn't true. I've heard that used to be true, before I ever had a Polar (which has been over two years now) but the new ones you can change the battery yourself.
  • rrlwelter
    rrlwelter Posts: 40 Member
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    Edited to add: The reason I got a Timex was because Polar makes you send your device back to them (and wait several weeks) in order to replace the batteries and the Timex can be changed in a watch shop.
    [/quote]

    That depends on the model - my Polar is changeable at any watch store, the main reason I chose it over other Polar models.
  • bizco
    bizco Posts: 1,949 Member
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    I also own a Timex and it's incredibly INACCURATE! I reduce whatever it says by half, I then compare that number to MFP's default database for "Aerobics, general" and log whichever is lower. If you're bike riding, look that up in the database and compare.
  • CJ_Holmes
    CJ_Holmes Posts: 759 Member
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    I used to have a Polar, and didn't want to send it in for new batteries so I got a Timex. The numbers seemed crazy high! I figured out a workaround by changing my weight in the the user set-up. I experimented with a few different weights until I got numbers that matched my calorie burns from past similar activities. My HRM now thinks I weigh 100 pounds (I weigh 145) but the burns seem accurate.
  • heybales
    heybales Posts: 18,842 Member
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    I used to have a Polar, and didn't want to send it in for new batteries so I got a Timex. The numbers seemed crazy high! I figured out a workaround by changing my weight in the the user set-up. I experimented with a few different weights until I got numbers that matched my calorie burns from past similar activities. My HRM now thinks I weigh 100 pounds (I weigh 145) but the burns seem accurate.

    Very good method and valid.

    I tried to figure out what study formula Timex must have been using, because they don't gather enough stats for most of the studies that estimate VO2max or calorie burns.

    But besides making it match the Polar, you can also try to make it match best estimate, that is better that HRM.
    Nice thing using this method. Test for 10 min. Adjust weight, test another 10, ect.
    All at perhaps just a fast 4 mph level walk - depending on fitness level. Reaching about 120 bpm would be best to compare.

    http://www.myfitnesspal.com/topics/show/774337-how-to-test-hrm-for-how-accurate-calorie-burn-is
  • cazattack2
    cazattack2 Posts: 37 Member
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    I think it's generally safe to estimate that you burn 1 cal/minute sleeping, and about 8-12/min when your heart rate is in the ideal range. At least for me. If you're hrm is displaying much higher than 12 cals/min, i'd say its wrong.
  • erinjohns315
    erinjohns315 Posts: 6 Member
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    Thank you all for your help! I used an online calculator (as suggested by one of you) and my calories burned came out to be half of what my HRM monitor said. I'm going to adjust the weight setting on it over the next few days and find one that is more accurate.
  • erinjohns315
    erinjohns315 Posts: 6 Member
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    Or maybe it's time for a new HRM.
  • gerla_k
    gerla_k Posts: 495 Member
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    check the batteries. i know Polar HRM will have wierd readings if the battery is about to die.
  • gerla_k
    gerla_k Posts: 495 Member
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    Edited to add: The reason I got a Timex was because Polar makes you send your device back to them (and wait several weeks) in order to replace the batteries and the Timex can be changed in a watch shop.



    That's not really true. I own a FT4, bought it about 3 years ago. I just changed my batteries myself cost me $7. I know that some say that once you open it it's no more waterproof, but i don't use mine for swimming anyways, so i really didn't care.

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