THIS is why HRMs have limited use for tracking calories

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Azdak
Azdak Posts: 8,281 Member
in Fitness and Exercise
The entire concept of using heart rate as means of estimating exercise calories is based on the relationship between heart rate (HR) and oxygen uptake (VO2) during steady-state aerobic exercise.

During steady-state aerobic exercise, there is a relatively consistent relationship between HR and VO2. Working at "X%" of HRmax usually means that one is working at "Y%" of VO2 max. If you know your VO2max and your true HRmax, then you can use that relationship to estimate VO2 during exercise--which means that you can also estimate calories, since calories burned is based on VO2 times body weight.

Once you leave the realm of steady-state aerobic exercise, however, accuracy of HRMs deteriorates rapidly. To understand why, you need to look at this chart:

HRVO2graph_zps6e180fba.jpg

The chart shows the percentage of VO2max that occurs when heart rate is at 85% of max HR reserve during various activities.

As you can see, it's quite a spread. The red bar is the heart rate--here, set at 85% max HR reserve. The blue bar is steady-state cardio. As you can see, steady-state cardio is the closest match.

While a heart rate of 85% of max corresponds to 75%-80% VO2 max during steady-state cardio, by the time you get to lifting heavy weights, that same heart rate of 85% of max corresponds to only 21% of VO2max.

The HRM doesn't know the difference--it is programmed to display a calorie number based on whatever heart rate it senses. It cannot detect the type of activity. This is why HRM calorie numbers for many non-steady-state-aerobic activities are useless.

The same situation is also true during thermal stress. Heart rate is elevated, while VO2 is not. That's why the inflated calorie claims for activities such as hot yoga are such nonsense.

For some reason, even though this is exercise physiology 101, many so-called "fitness experts" do not understand this. Now that you do, this is one way to evaluate the credibility of a trainer or fitness author. If they say something like "lifting weights can be cardio if you move quickly between exercises to keep your heart rate up", you know you are listening to someone with a serious deficit in their knowledge base--and you'll have to wonder what else they don't know.
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Replies

  • MsEndomorph
    MsEndomorph Posts: 604 Member
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    Thank you for posting this!
  • JayStu
    JayStu Posts: 332 Member
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    I'm sorry but this just confused the hell out of me. So are you saying I shouldn't use the calories burned that my HRM shows when tracking exercise.
  • adairt1
    adairt1 Posts: 14
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    Sorry if this is a dumb question but does this mean that the HRMs are best suited for steady cardio activities? Would they be relatively accurate for it?
  • composite
    composite Posts: 138 Member
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    Azdak is saying that it's a more accurate measure for steady state cardio than other types of exercise.

    I'm interested in the deification for "steady state cardio" though. How does consistently paced medium intensity cardio stack up against intervals (cardio) in terms of accuracy? The name "steady state cardio" does not suggest intervals to me but I'm wondering if I'm being to literal?

    Also what are your sources for this information in general?
  • MsEndomorph
    MsEndomorph Posts: 604 Member
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    Your HRM's manual will say it's meant only for steady state cardio because HRMs use a formula made specifically for those exercises and those exercises only.

    So if you look at the chart, you'll see that using a HRM for anything will give you a falsely elevated calorie burn. I wear mine during weight lifting (because I use it for my warm up and to do cardio afterward) and it will easily tell me I burned 400 cals in 30 minutes, when the reality is I probably burned 100 or less.
  • Azdak
    Azdak Posts: 8,281 Member
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    Azdak is saying that it's a more accurate measure for steady state cardio than other types of exercise.

    I'm interested in the deification for "steady state cardio" though. How does consistently paced medium intensity cardio stack up against intervals (cardio) in terms of accuracy? The name "steady state cardio" does not suggest intervals to me but I'm wondering if I'm being to literal?

    Also what are your sources for this information in general?

    "Steady state" cardio means exactly that--sustained cardio that is done under steady-state conditions, commonly defined as 40%-50% of VO2 max up to what is commonly referred to as the "lactate threshold"--or about 65%-75% of VO2 max, depending on the individual.

    As you start moving away from deriving most of your exercise energy from the "aerobic" (or TCA) cycle, the accuracy of HRM calorie counts will start to deteriorate. That would include HIIT. So, yes, HRM calorie counts are less accurate for interval training.

    My sources are: A) my general education in the field of exercise physiology (which is what I do for a living) and B) measurements of VO2 taken from various research studies. Often these studies are not designed to measure VO2--they record it as part of the general data gathering--but if you know how to read the data, the information is there.
  • PikaKnight
    PikaKnight Posts: 34,971 Member
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    I just do -30% from the cal burn given and log it that way. MFP's calculations end up being pretty close and most of the time I go with whichever is lower.
  • Doodlewhopper
    Doodlewhopper Posts: 1,018 Member
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    I'm sorry but this just confused the hell out of me. So are you saying I shouldn't use the calories burned that my HRM shows when tracking exercise.

    Depends on the exercise. The OP states: <SNIP>
    The entire concept of using heart rate as means of estimating exercise calories is based on the relationship between heart rate (HR) and oxygen uptake (VO2) during steady-state aerobic exercise.

    During steady-state aerobic exercise, there is a relatively consistent relationship between HR and VO2.

    Visualize a car equipped with a tachometer. Cruising at a constant speed on the open highway one could more accurately estimate fuel expenditure per mile merely by monitoring the tach.

    Not so in city driving because of inconsistent demands on the power plant. (do I make sense or do I only think I do? LOL)
  • Azdak
    Azdak Posts: 8,281 Member
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    Sorry if this is a dumb question but does this mean that the HRMs are best suited for steady cardio activities? Would they be relatively accurate for it?

    Yes, those are the only conditions under which they should be considered reasonably accurate.

    Now, that also assumes that they are: A) a quality model from a company that does their own research to develop their algorithms (e.g. Polar) and B) set up properly. To be most accurate, and HRM must be programmed with your actual HRmax and your actual VO2max. Those numbers are not always easily obtainable and some lower-level models (even Polars) do not allow you to manually input these variables. In that case, I don't know how you can make them more accurate.

    For example, an HRM will set a default HRmax of 220-age (or close to that). We know that in the normal population, HRmax can vary 20-30 beats from that "220-age" number. If your HRM has a default HRmax of 180, for example, but your actual HRmax is 210, the HRM will substantially overestimate your calories burned--it thinks you are working much harder than you are.
  • bumblebums
    bumblebums Posts: 2,181 Member
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    An excellent point, Azdak. It's stuff like this that led me to stop tracking my exercise calories altogether, especially when I decreased the amount of steady state cardio I do in favor of more anaerobic activity.
  • getfitgal123
    getfitgal123 Posts: 267 Member
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    Interesting. Thanks for posting.
    I do kettlebell circuit workouts with a trainer 3 times per week and don't wear my HRM as I suspected this to be the case. I never know how to track calories burned... whole workout with warm up and cool-down is usually about 45-60 minutes, I usually just use MFP's estimation for 20 minutes of circuit training to be conservative.

    What about running intervals on the treadmill? Is that considered steady-state? Can I rely on HRM for that? I usually do 3:1 intervals of slow jog (4.5-5.0 mph) and fast run (8.0-8.5 mph).
  • getfitgal123
    getfitgal123 Posts: 267 Member
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    My bad - I guess you already answered my question! :)



    As you start moving away from deriving most of your exercise energy from the "aerobic" (or TCA) cycle, the accuracy of HRM calorie counts will start to deteriorate. That would include HIIT. So, yes, HRM calorie counts are less accurate for interval training.

  • RunFarLiveHappy
    RunFarLiveHappy Posts: 805 Member
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    I do not dispute any information in the original post. However we have to use what tools we have available to us to come up with our best approximation of calories burned. I personally stopped using my HRM for anything other than cardio (99% of the time this is running) and do not use it at all for strength training (stronglifts 5x5). What works best for me is to gather TDEE information from my activity monitor (Jawbone UP band) and when I am doing intentional cardio exercise I use my Polar USA FT4 HRM. I then use TDEE - 20% as a baseline for total calories to consume for the day. If what you're doing is successful for you, meaning that you're getting positive results (losing BF%, losing inches, losing pounds, etc.) don't change what isn't broken. If you aren't seeing results it could quite possibly be because you are inaccurately calculating calories burned or activity level. Just as well you could be inaccurately calculating your calorie consumption...
  • Azdak
    Azdak Posts: 8,281 Member
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    An excellent point, Azdak. It's stuff like this that led me to stop tracking my exercise calories altogether, especially when I decreased the amount of steady state cardio I do in favor of more anaerobic activity.

    Usually when you get to the point where you are doing more anaerobic work, you are reaching a point with your fat:muscle ratio where fat mobilization becomes a greater obstacle than fat oxidation, and large calorie deficits can be counterproductive.

    So the type of exercise that is most effective--lifting, metabolic workouts, etc--is the type in which calorie expenditure is the least quantifiable--by any means.

    So, if you are running a deficit at all, it needs to be a small one, often outside the level of accuracy that is possible by the methods that average person uses--i.e. estimating calories burned during exercise, food labels. At that point, I think estimates of exercise calories in general -- by whatever method used -- become mostly an exercise in futility and the ol' trial-and-error method is likely to be as effective as anything else.
  • composite
    composite Posts: 138 Member
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    Just to say now I've never bothered with wearing a HRM for lifting. In fact I don't even count lifting as any sort of calorie burn tbh. I'm more interested in this at the other end of the scale.
    "Steady state" cardio means exactly that--sustained cardio that is done under steady-state conditions, commonly defined as 40%-50% of VO2 max up to what is commonly referred to as the "lactate threshold"--or about 65%-75% of VO2 max, depending on the individual.

    As you start moving away from deriving most of your exercise energy from the "aerobic" (or TCA) cycle, the accuracy of HRM calorie counts will start to deteriorate. That would include HIIT. So, yes, HRM calorie counts are less accurate for interval training.

    Are you saying then that when you go over threshold the relationship between HR and VO2 Max changes in terms of calories burnt?

    I'm confused in that when you lift weights you feel your heart rate go up but you don't really get out of breath. That's an easy one to understand in relation to your graph. When I'm doing the sprint intervals on the bike my heart rate goes up and I get out of breath and must be closer to my VO2 Max.

    In that case then are you saying that at that end of the scale the HRM is under estimating if at the lower end (weight lifting) it's over estimating?

    Alternatively am I just completely confused and my question doesn't even make sense?
  • jzammetti
    jzammetti Posts: 1,956 Member
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    I'm sorry but this just confused the hell out of me. So are you saying I shouldn't use the calories burned that my HRM shows when tracking exercise.

    I did and relied upon them for a long time until I got my Bodymedia Fit - my HRM was WAAAYYYY overestimating and I was eating at or above maintenance for months. Now with the BMFit I have a much closer estimate and in two weeks lost 1.5 pounds (exactly how much the caloric deficit predicted). The HRM is a good tool fr cardio fitness...but not so much for calorie counting.
  • sungod916
    sungod916 Posts: 8 Member
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    I use an HRM during cardio and weight lifting just get a general sense of how hard my heart is working.
    I don't take the calories burned number too seriously.
    I wouldn't completely dismiss using an HRM based on this post because they do add value to exercise by helping you see how hard you're working... just don't trust the calorie count if it says you burned 1000 calories and then go eat back 800 of those.
    It's usually off.
  • jollyjoe321
    jollyjoe321 Posts: 529 Member
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    Me and my friend weigh similar.

    On a treadmill, we measured our heart rates at 12 km/h, his was sat at 178, mine was around 145, I'm not entirely convinced he was burning a great deal more calories than me.
  • sungod916
    sungod916 Posts: 8 Member
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    What if you weigh the same but he's 20% body fat and you're 14% body fat?
    You've got more muscle than he does.
    I'm not sure the HRM counts this but WHAT IF MAN! LOL
  • bumblebums
    bumblebums Posts: 2,181 Member
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    An excellent point, Azdak. It's stuff like this that led me to stop tracking my exercise calories altogether, especially when I decreased the amount of steady state cardio I do in favor of more anaerobic activity.

    Usually when you get to the point where you are doing more anaerobic work, you are reaching a point with your fat:muscle ratio where fat mobilization becomes a greater obstacle than fat oxidation, and large calorie deficits can be counterproductive.

    So the type of exercise that is most effective--lifting, metabolic workouts, etc--is the type in which calorie expenditure is the least quantifiable--by any means.

    So, if you are running a deficit at all, it needs to be a small one, often outside the level of accuracy that is possible by the methods that average person uses--i.e. estimating calories burned during exercise, food labels. At that point, I think estimates of exercise calories in general -- by whatever method used -- become mostly an exercise in futility and the ol' trial-and-error method is likely to be as effective as anything else.

    Exactly. I've worked out my TDEE by tracking my weight given a fixed intake level, and I've been maintaining the same weight for months now without tracking my exercise calories. If I wanted to lose more weight, I would simply cut calories by maybe 200/day without changing anything else. It all works well without using an HRM or the MFP exercise calorie guesstimator.

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