Question on HRM accuracy

vnakkar
vnakkar Posts: 30
in Fitness and Exercise
I have a Polar FT7, I have a question about accuracy between the wrist computer and the Life Fitness Elliptical I was on. Here were some other sessions that had be believing the wrist computer was fairly accurate.


When I walk the dogs, 30 minutes, 1.5 miles here I what I have:
MFP: 132 cal
MapMyWalk iPhone APP: 140 Cal
HRM: 190 - RMR = 145 cal
Sounds good!

30 Minute lifting and 30 minutes circuit training
MFP: 441 cal
HRM 550 - RMR = 460
Sounds good to me!

35 Minutes on the Elliptical
Machine: 300 cal
HRM: 446 - RMR = 394
HR on the machine and watch were the same.

30% difference falls outside a reasonable margin of error.

Who do I believe?

Thx!

Replies

  • mrandolph69
    mrandolph69 Posts: 197 Member
    I have a Polar FT7, I have a question about accuracy between the wrist computer and the Life Fitness Elliptical I was on. Here were some other sessions that had be believing the wrist computer was fairly accurate.


    When I walk the dogs, 30 minutes, 1.5 miles here I what I have:
    MFP: 132 cal
    MapMyWalk iPhone APP: 140 Cal
    HRM: 190 - RMR = 145 cal
    Sounds good!

    30 Minute lifting and 30 minutes circuit training
    MFP: 441 cal
    HRM 550 - RMR = 460
    Sounds good to me!

    35 Minutes on the Elliptical
    Machine: 300 cal
    HRM: 446 - RMR = 394
    HR on the machine and watch were the same.

    30% difference falls outside a reasonable margin of error.

    Who do I believe?

    Thx!

    I would always go with the HRM's numbers since (assuming you entered in your personal info accurately) it is basing the calorie estimate on more info, namely your heart rate. MFP obviously doesn't know how hard your heart was working in any given workout so it's number is an estimate that is (hopefully) in the ballpark for most people. Although it is in the ballpark, it is still just a guess. I always go with my HRM's numbers (also Polar FT7.) Keep in mind, though that even an HRM is not 100% accurate.

    You also noted that the HRM and machine read the same. If your machine is set up to do so (and most are these days) it will actually use the reading from your HRM (the same way your FT7 watch is reading the signal from the chest strap.)
  • iWaffle
    iWaffle Posts: 2,208 Member
    They're both estimates but I think the Polar is closer to being accurate than anything. I have an FT7 as well and it's really good on calorie burn estimates. When I run I'm burning 700 - 800 (Today nearly 1,000) calories according to the FT7. I eat all the calories back and I'm not gaining weight so it must be pretty close to accurate.

    The big difference is having the data on your heart rate. Your Polar is a dedicated machine with one purpose, to read heart rate and calculate calories burned from that.
  • vnakkar
    vnakkar Posts: 30
    I included the first two groupings because knowing they're estimates I was surprised they were all in the same close range.

    The elliptical was reading the HR from the strap, as I wasn't using the hand grips so I was surprised they came up with such wildly different numbers given the same HR.


    However, in other news I saw something interesting. I was looking at my exercise diary and saw a correlation.

    I used the elliptical on 9/26.. I didn't have my HRM monitor yet, it came the day after.

    9/26: 40 minutes, 300 calories. Heart rate ~135

    Yesterday I wanted to get done faster, so I put my target heart rate to 150

    10/3: 40 minutes, 300 calories. Heart rate ~150

    I think I'm sticking with the HRM calories from here on out!
  • TravisBurns
    TravisBurns Posts: 353 Member
    I had a forum similar to this. My HRM is a lot cheaper and not as nice or fancy as those polars. but It has a chest strap and everything and when I calculate, I use my age and height and everything. But my numbers almost seem too generous, although I do bust my *kitten*
  • Micheetah
    Micheetah Posts: 184 Member
    When I do the eliptical, it always tells me I burn WAY more than my HRM tells me I'm burning, which is weird because its taking my HR the whole time as well. my HRM will say 100 cal burned, the LifeFitness will say almost 200, its crazy different.

    I still chose to listen to my HRM, safer with the lower cal burn number for logging purposes.
  • nphect
    nphect Posts: 474
    crap is all estimates anyhow. your just going to have to either go with the lower numbers, or average it out, or just stick with one thing. i suggest sticking with one way and doing it that way, so you can adjust accordingly.
  • MinnieInMaine
    MinnieInMaine Posts: 6,400 Member
    The reason the HRM is more accurate than the machines is that it has more of your personal info. You may be able to enter weight and age into your machine but that's usually the extent of the info - it doesn't know your gender or height like the HRM does. Not sure how much of a role height plays but gender is definitely important because generally men will burn more than women due to more muscle mass.
  • Azdak
    Azdak Posts: 8,281 Member
    I have a Polar FT7, I have a question about accuracy between the wrist computer and the Life Fitness Elliptical I was on. Here were some other sessions that had be believing the wrist computer was fairly accurate.


    When I walk the dogs, 30 minutes, 1.5 miles here I what I have:
    MFP: 132 cal
    MapMyWalk iPhone APP: 140 Cal
    HRM: 190 - RMR = 145 cal
    Sounds good!

    30 Minute lifting and 30 minutes circuit training
    MFP: 441 cal
    HRM 550 - RMR = 460
    Sounds good to me!

    35 Minutes on the Elliptical
    Machine: 300 cal
    HRM: 446 - RMR = 394
    HR on the machine and watch were the same.

    30% difference falls outside a reasonable margin of error.

    Who do I believe?

    Thx!

    Well, your first two examples do not provide a very good standard of comparison, since the 1.5 mile walk doesn't burn much at all, so none of the numbers will be that different, and HRMs are much less accurate/not accurate at all for things like circuit trainin/weight training (and the MFP numbers for those activities are not any better).

    The answer to the elliptical question depends on the model of the elliptical and the software version. If you are on a 9500HRR (very old), 91X, or Integrity Classic model (the last two are the most common ones found in health clubs), then the calorie burn numbers are a good 25% too high. If you are on a later model 95X, or the newer 95 Elevation series cross trainers, then the numbers are very accurate, likely more accurate than your HRM. On those machines, Life Fitness developed machine-specific algorithms for estimating calories.

    Given that the LF number is much lower, and your HRM numbers are kind of high across the board, I would suspect that the cross trainer numbers are more accurate.
  • Azdak
    Azdak Posts: 8,281 Member
    The reason the HRM is more accurate than the machines is that it has more of your personal info. You may be able to enter weight and age into your machine but that's usually the extent of the info - it doesn't know your gender or height like the HRM does. Not sure how much of a role height plays but gender is definitely important because generally men will burn more than women due to more muscle mass.

    HRMs need more data because they do not measure workload--the extra factors make their equations more accurate, but that's a math thing-it has little to do with actual calorie expenditure.

    Machines measure actual workload. For some cardiovascular activities, the relationship between workload and oxygen uptake (calorie burn) is known and fairly reliable. So in some cases, the readings on machines are more accurate and consistent than HRM numbers. The reason why some machines are inaccurate is that they use outdated, inappropriate, or inaccurate equations to translate workload into calories--not because they don't have enough information. With the right equation, workload and body weight are all you need--heart rate is irrelevant.
  • mrwalker80
    mrwalker80 Posts: 6
    I don't use a HRM...yet. I do use LF ellipticals, bikes, and treadmills. What I've ended up doing is when I log, I round down usually by 50 calories. So, if 45 minutes on the elliptical is ~400 calories, I'll log 350.

    Where I really guess is at my boot camp sessions. Going twice a week for 60 minutes each session (with roughly 5-8 minutes total rest), MFP gives a huge a calorie burn number. So, I round down very generously. I'll usually enter 30-35 minutes worth. This is where I would like to use a HRM to get an idea for my HR because I never check it manually. I'll admit, I rarely eat back calories at this point so I put myself in big deficits, so its probably not as crucial for me to have close-to-exact numbers as someone who does eat back. And I also never log calories burned when doing weight training. Probably not the best advice!

    In the end, nphect's suggestion is best: find one to monitor and use it as a trend.

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