Another heart rate to calories burned question

pizzle421
pizzle421 Posts: 16 Member
in Fitness and Exercise
I've noticed a fair amount of fluctuation in my heart rate for the same exercise and same general exertion.

For example, yesterday I did 30 minutes on the elliptical. My heart rate ranged between 135-155 for almost the entire duration of the exercise.

Today, same thing, I had to push myself harder to exceed 129.

A few questions.

1. Am I the only one to notice how much more gas it takes (evident by rate rate when wearing my polar watch/strap and how I feel) when you're down in calories? Wed-Saturday I was at a solid (yet safe in theory) caloric deficit. It's also worth noting that I had lifted Saturday. Exercise Sunday was rough.

I had to ~3000 calories Sunday (yesterday), and this evening cardio was a breeze (again - evident by HRM).

2. This got me thinking about calories burned on my watch. If it's just more challenging day one to exercise (due to external factors) and my heart rate is increased - does that give a false boost to my calories burned? That would also include doing cardio after lifting. Because my heart rate is already elevated and I'm already fatigued (increasing my heart rate and calories burned according to my HRM) am I really burning more calories?

Thanks in advance.

Replies

  • sijomial
    sijomial Posts: 19,809 Member
    If you are exerting the same force for the same duration on the same piece of equipment your actual calories burned will be the same.

    That your heart rate is different just shows the limitation of estimating calories from heart rate.
    All sorts of things influence HR including getting hot, caffeine, stress, fitness, hydration and just having an off day.....
    My HRM is calibrated with my tested VO2 max and max HR and will match a power meter almost exactly - until I get hot and my HR rises for the same power output and the numbers then diverge by about 20%.

    I train with power meter equipped machines quite a bit and it's interesting to see the vast differences between actual calorie output (power) and HR.
    The other day I was putting out a steady 200 watts at about 140bpm and the guy next to me was putting out 230 watts at 130bpm. With a basic HRM it would assume I was burning more calories than him.

    On the other hand I've trained next to someone hitting 180bpm but putting out half my power output at when I'm at 150bpm.
  • beemerphile1
    beemerphile1 Posts: 1,710 Member
    A number of things will increase your heart rate on a given day;
    calorie deficit
    tired/poor sleep
    dehydration
  • BrianSharpe
    BrianSharpe Posts: 9,248 Member
    You've uncovered one of the deficiencies in how many HRMs calculate calories expended. There is not a direct correlation between heart rate and calories burned. Two runners of equal weight will burn the virtually the same number of calories running the same distance (mass x distance) even if one is fitter than the other and has a lower heart rate.
  • pizzle421
    pizzle421 Posts: 16 Member
    BrianSharpe wrote: »
    You've uncovered one of the deficiencies in how many HRMs calculate calories expended. There is not a direct correlation between heart rate and calories burned. Two runners of equal weight will burn the virtually the same number of calories running the same distance (mass x distance) even if one is fitter than the other and has a lower heart rate.

    That's interesting to know. So energy expenditure and fitness don't factor in?
  • lemmie177
    lemmie177 Posts: 479 Member
    pizzle421 wrote: »
    BrianSharpe wrote: »
    You've uncovered one of the deficiencies in how many HRMs calculate calories expended. There is not a direct correlation between heart rate and calories burned. Two runners of equal weight will burn the virtually the same number of calories running the same distance (mass x distance) even if one is fitter than the other and has a lower heart rate.

    That's interesting to know. So energy expenditure and fitness don't factor in?
    I believe fitness is more about an individual's capacity to do work. The fitter runner may feel less fatigued at the end of the run, but will still have burned roughly the same # calories. There's also adaptation to a particular activity, which would improve the efficiency of applied calories. In this case, a more practiced runner may be able to go the same distance using less calories, because they have less wasted movement.

    We use HR as a very rough estimate of oxygen consumption, which is an indirect measurement of energy expenditure. It actually estimates best during steady state, lower-body dominant cardio. So, in addition to all the external factors you found, it also gives false boosts during strength workouts or any kind of stop-and-go training, since the elevated HR is not actually reflective of oxygen consumption.

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