HRM monitor accuracy?

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ashorey87
ashorey87 Posts: 173 Member
in Fitness and Exercise
Tested out my new Polar FT7 - how accurate are these for calories burned? The difference between my HRM and treadmill reading is astronomical! HRM says 653 and treadmill says 297. Can I really trust that I burned 650 cals doing 50 mins of cardio?!

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  • ashorey87
    ashorey87 Posts: 173 Member
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    r0oqatut87qm.jpeg
  • MeanderingMammal
    MeanderingMammal Posts: 7,866 Member
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    3.29 miles in 50 minutes?

    About 250-260cals would be optimistic, so I'd veer towards the machine.

    Were you going at a steady pace or intervals?
  • ashorey87
    ashorey87 Posts: 173 Member
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    Intervals. My cardio ability is awful. I was dripping sweat and dying the entire time lol. And I'm a smoker (shame on me), so I'm sure my heart and lungs were working harder than a normal person who's in shape.
  • Hornsby
    Hornsby Posts: 10,322 Member
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    HRMs aren't accurate for intervals. Machine it is.
  • ashorey87
    ashorey87 Posts: 173 Member
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    Hornsby wrote: »
    HRMs aren't accurate for intervals. Machine it is.

    Great, thanks! I'm a newbie to HRMs and I thought there was no way I could burn that much. So they are really only accurate for consistent cardio?
  • MeanderingMammal
    MeanderingMammal Posts: 7,866 Member
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    ashorey87 wrote: »
    Intervals. My cardio ability is awful. I was dripping sweat and dying the entire time lol. And I'm a smoker (shame on me), so I'm sure my heart and lungs were working harder than a normal person who's in shape.

    OK, so HRMs start to overestimate as soon as HR starts to fluctuate. Given that you were doing a 10 minute kilometre that suggests walk/ run intervals, so the degree of overestimation will be quite high as a result.

    You've also identified that as a smoker you're contributing to poor CV performance. Your stroke volume will be compromised, and your blood oxygen concentration will be poor, both of which lead to an increased heart rate for an equivalent amount of work. If you had a more sophisticated HRM you could go for a lab test to find out your VO2Max, but it's pretty much moot at the moment given the poor CV performance.

    If you want to improve both stroke volume and blood oxygen concentration, you'd get more benefit from steady state work, although if you're restricted to a treadmill I can recognise that is incredibly boring.
  • BrianSharpe
    BrianSharpe Posts: 9,248 Member
    edited March 2016
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    Depending on your weight I'd even say that 300 cals for a 3.3 mile walk is optimistic unless the treadmill was at a fairly good incline.

    Runners World suggests the following formula for walking .30 x weight(in lbs) x distance (in miles) (or 30 cal per 100lbs per mile) this gives you your net calories expended (ie additional calories attributable to exercise, many machine give you the gross which includes your BMR)
  • ashorey87
    ashorey87 Posts: 173 Member
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    Thanks for your input guys, much appreciated!
  • darthsogogi
    darthsogogi Posts: 5 Member
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    For anyone else considering what to buy, the great science folks at Guru Performance recently conducted some tests on a few different devices:
    https://www.youtube.com/watch?v=3mUejI-P_ZU
  • Chieflrg
    Chieflrg Posts: 9,097 Member
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    Neither are highly accurate, although at a steady state of cardiovascular a HRM will get you in the back park to at least adjust.

    Remember treadmill is not expending the same amount of energy as running on a stationary surface.

    The formula for walking that @BrianSharpe mentioned for walking or if running...
    .64 x (bodyweight in pounds) x miles will get you awful close.
  • robertw486
    robertw486 Posts: 2,388 Member
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    It might be worth keeping track of your walking vs running differences, then using the formulas provided from the Runners World articles. That would nail down your close estimate, and give you an idea of how close the machine is.

    I suspect the machine will be higher, as all Precor machines that I'm aware of are designed to display gross calorie burn. That would essentially make them display 1 met value above net calorie burn if that is the case.


    But in any case, a good real world example of error in the HRM, while many here on the forums always claim that the machines can't be trusted. I'm to the point I trust nothing I can't verify against a more solid and proven number.

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