HRM overestimates calories burnt during interval training?

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butterflyknife
butterflyknife Posts: 12 Member
in Fitness and Exercise
I have a Polar FT60, which purports to calculate the calories I've burnt during workouts from my heart rate, VO2max, gender etc.

My question in short is: Will my HRM overestimate the amount of work I'm doing (ie calories I've burnt) in the "rest" intervals due to my heart rate being elevated from the previous "sprint" interval?

My reasoning for suspecting this is as follows:

- when I walk at a steady 4kmph, my HR is say 100bpm. The HRM reads this rate at converts to a certain number of cal/hour, say 200.

-now suppose I sprint HARD for a minute, and then slow down and start walking at 4km/h again. This time, my HR is 160bpm on average. The HRM reads this rate, and because it is 160 rather than 100, thinks I'm jogging, and so converts to a higher cal/hour than before, say 300.

Does it make sense that I'm walking at exactly the same speed in both cases, but that I'd be burning more calories in the latter case just because my heart rate is higher?

Replies

  • Ke22yB
    Ke22yB Posts: 969 Member
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    Since your heart rate is still elevated you are probably burning more than if you kept at a steady pace. I found the afterburn of running hard my breathing is faster and harder and my HR is higher. As my physical conditioning improved my recovery was much faster and my HR was lower at a faster running pace so my calories burned kept coming down
  • MeanderingMammal
    MeanderingMammal Posts: 7,866 Member
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    I have a Polar FT60, which purports to calculate the calories I've burnt during workouts from my heart rate, VO2max, gender etc.

    It extrapolates from that data to give you an approximation of calorie expenditure,
    My question in short is: Will my HRM overestimate the amount of work I'm doing (ie calories I've burnt) in the "rest" intervals due to my heart rate being elevated from the previous "sprint" interval?

    Yes, the rapid transition in HR doesn't really translate to the algorithm that it uses to extrapolate expenditure.

    The effect of that really depends on how much interval work you're doing within a session. From the perspective of running, the impact within a session isn't that high, perhaps an extra 60 or so calories within a 600-800 cal expenditure.

    Last nights session for me was:

    15 minutes warm up at 6 mins per km
    1 km at 4 min per km
    3 mins at recovery
    1km at fast pace
    3 mins recovery
    1 km fast
    15 minutes recovery

    In that instance the over-estimation wouldn't be huge as the transitions whilst sharp are then into a sustained period.

    Last weeks interval session was

    10 minutes warm up at recovery
    20 seconds max effort to 3 mins per km
    60 seconds recovery
    Repeat * 10
    15 minutes cool down at recovery

    In that instance it's a larger error and has more significance within the session

    Before that it was:

    10 minutes warm up at recovery
    400 meters max effort at between 3 mins and 3 mins 15 per km
    400 metres at recovery
    Repeat * 6
    15 minutes cool down at recovery

    Again a more significant impact

    Given that these are all wrapped up in a wider session I wouldn't be too worked up about it.
  • cwolfman13
    cwolfman13 Posts: 41,874 Member
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    I have a Polar FT60, which purports to calculate the calories I've burnt during workouts from my heart rate, VO2max, gender etc.

    My question in short is: Will my HRM overestimate the amount of work I'm doing (ie calories I've burnt) in the "rest" intervals due to my heart rate being elevated from the previous "sprint" interval?

    My reasoning for suspecting this is as follows:

    - when I walk at a steady 4kmph, my HR is say 100bpm. The HRM reads this rate at converts to a certain number of cal/hour, say 200.

    -now suppose I sprint HARD for a minute, and then slow down and start walking at 4km/h again. This time, my HR is 160bpm on average. The HRM reads this rate, and because it is 160 rather than 100, thinks I'm jogging, and so converts to a higher cal/hour than before, say 300.

    Does it make sense that I'm walking at exactly the same speed in both cases, but that I'd be burning more calories in the latter case just because my heart rate is higher?

    Yes...the further away you get from a steady state aerobic event, the less accurate a HRM is for calorie burn. You can still get something reasonable for an estimate, but you're going to have to make more of an allowance for error than you would if you were doing steady state cardio...but really, it's going to depend on what your intervals look like. Keep in mind that regardless, you would want to at minimum deduct your basal calories.
    Since your heart rate is still elevated you are probably burning more than if you kept at a steady pace.

    There is no direct correlation between your HR and burning calories. If there was, I'd just have someone come into my office and give me a good scare every 5 minutes and call it a day.
  • butterflyknife
    butterflyknife Posts: 12 Member
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    Since your heart rate is still elevated you are probably burning more than if you kept at a steady pace.

    There is no direct correlation between your HR and burning calories. If there was, I'd just have someone come into my office and give me a good scare every 5 minutes and call it a day.

    Oh, dammit. Guess I'd better cut back on the ciggies and crack cocaine then :-P

    Thanks all for your help.
  • Eric_DeCastro
    Eric_DeCastro Posts: 767 Member
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    I think it's just an estimation since your heart rate is increased it assumes you are doing some physical activity. but it's the closest thing I have to "count" burned calories and i use it every day. as long as I don't use one method, then a diferent one the next and so on, it will be consistent.

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