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Heartrate and caloric burn relationship - How much does HR actually influence it?

So I'm having trouble pinning down a somewhat informed/scientific answer to this question -

Given two identical people (same body composition, etc.) who are performing the same *light* activity (e.g., Office work, a hundred steps here and there, and NOT exercise), how big of a difference (in very, very rough percentage terms) would there be between their caloric burns if one was at a HR of 70 bpm and the other had one of 90 bpm?

I know that in the real world, this would ultimately be dependent on a number of factors, but what if HR was the only variable?
edited June 2016
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Replies

• Posts: 9,535Member Member
Heart rate is highly individual. Take two people of the same age and fitness and you're likely to find wildly different max and lactate threshold heart rates. Then it's also influenced by things like heat, mood, hydration, caffeine intake, etc. During exercise, your heart rate will rise while you maintain a specific amount of effort, and it's really the effort that's responsible for burning energy. Heart rate is your body's reaction to that effort.

The best calories from HR formulas use HRV not pulse rate to tell things like whether you're working above or below your threshold, how much energy you're using from aerobic vs anaerobic pathways, etc.
edited June 2016
• Posts: 13,080Member Member
The calorie burn in your case (In nearly all scenarios) is simply weight moved x distance. The extra calories, if any, from the heart rate increase is negligible.
• Posts: 9,535Member Member
Let me put that another way: on a bike, you need maintain an average output of ~135 watts to burn 500 kCal per hour. That's true no matter what your heart rate is while you're doing it.
• Posts: 933Member Member
Let me put that another way: on a bike, you need maintain an average output of ~135 watts to burn 500 kCal per hour. That's true no matter what your heart rate is while you're doing it.
Wouldn't that vary to individual based on weight? Also, that is measured at the pedals, correct?
Thanks for the replies so far, everyone.

Some background - I recently upgraded from a Fitbit Flex (no HR monitor) to a Fitbit Blaze (with HR) and I'm seeing caloric adjustments twice as much (or more) as I had before. I have a resting (according to the Blaze) HR of ~65, but during the day at work (Sitting at a desk much of the time) my HR fluctuates between 75 bpm up to the low-90s depending on stress/caffeine intake/etc.).

While I was using the Flex and targeting a 250/500 calorie deficit based on its numbers, I lost weight at a rate that was generally in line what would be expected (and was consistent with my hypothetical TDEE). But with these new values (at a similar activity level), I would have theoretically been at a 500-1000+ calorie deficit which seems absolutely crazy to me.

It makes sense to me that the only difference in the scenario I posed above would effectively be the amount of energy it would take for a heart to pump faster (plus whatever else that physiologically needs to happen), which as Waffle mentioned would be negligible.

However, Fitbit is clearly considering HR in their algorithms. I'm just wondering *why* they're doing that, and if there's any scientific validity to it. I'm guessing they assume that if the user has an elevated HR, they're more heavily active at a given moment?
edited June 2016
• Posts: 13,080Member Member
Garmin gives me just under 100 fewer calories for a 6 mile run with a HRM than without. They do factor your pulse into that apparently but I wouldn't hold that to be a major difference considering that's a full hour's worth of work. We're talking about potentially 1.6 calories per minute difference max.

There is a difference no doubt. Just not a vast difference or much worth worrying about unless you're trying to squeeze in an extra beer at the end of the day.

ETA: To beat the system I added on 0.2 miles so I always get over 1k calories. This difference is easy to overcome.

2nd ETA: Simply walking around? Not sure what the difference would be. Seems like it would be tiny.
edited June 2016
• Posts: 9,535Member Member
moe0303 wrote: »
Let me put that another way: on a bike, you need maintain an average output of ~135 watts to burn 500 kCal per hour. That's true no matter what your heart rate is while you're doing it.
Wouldn't that vary to individual based on weight? Also, that is measured at the pedals, correct?

It would not depend on the individual's weight. But a heavier cyclist is going to require more watts than a lighter one ride up a hill, so they'll usually burn more calories than a light rider because they're putting out more effort to go the same speed. But it's the effort not the HR that burns the calories. It'll differ by up to about 5 % on the individual's metabolic efficiency, but that's a pretty small amount.

You can measure power output on a bike at:

* the pedals (I do, it's easy to move pedals to another bike)
* the crank arms
* the chainrings
* the chain itself
* the rear wheel
* I'm probably leaving something out.

I hope that wasn't too convoluted an explanation.
edited June 2016
• Posts: 9,535Member Member
andrektan wrote: »
However, Fitbit is clearly considering HR in their algorithms. I'm just wondering *why* they're doing that, and if there's any scientific validity to it. I'm guessing they assume that if the user has an elevated HR, they're more heavily active at a given moment?

In general it's scientifically valid to say that if you're heart is doing 180 bpm you're using more energy than if it's going 80 bpm. The question is how much more energy?

When you exercise you use your muscles to do some kind of work, maybe your legs to run. As your exercise gets more intense, your leg muscles need more and more energy. They get a lot of it by using oxygen to release the energy stored in fat. That's why you breathe harder at higher intensity, to get more oxygen in, and it's why your heart rate increases, to pump oxygenated blood to your muscles. You can get to the point where this just doesn't supply enough energy so you keep doing it but also use glycogen which does not require oxygen. Most of the time you're using some aerobic and some anaerobic energy to exercise, but mostly aerobic until the intensity gets very high. Really clever HRM systems can figure out where that point is for you but this can't really be measured at the wrist.

A lot of things (Fitbits, Garmins, phone apps) factor HR in their calorie algorithms. Generally people consider a calorie estimate more accurate if HR was part of calculating it. But some algorithms are a lot better than others. And even then, sometimes a good algorithm gets put into a system that has some other bug and you wind up with gibberish anyway.

Since you know your weight loss agrees with the numbers before you upgraded, I'd say the old one was more accurate for you.
• Posts: 933Member Member
moe0303 wrote: »
Let me put that another way: on a bike, you need maintain an average output of ~135 watts to burn 500 kCal per hour. That's true no matter what your heart rate is while you're doing it.
Wouldn't that vary to individual based on weight? Also, that is measured at the pedals, correct?

It would not depend on the individual's weight. But a heavier cyclist is going to require more watts than a lighter one ride up a hill, so they'll usually burn more calories than a light rider because they're putting out more effort to go the same speed. But it's the effort not the HR that burns the calories. It'll differ by up to about 5 % on the individual's metabolic efficiency, but that's a pretty small amount.

You can measure power output on a bike at:

* the pedals (I do, it's easy to move pedals to another bike)
* the crank arms
* the chainrings
* the chain itself
* the rear wheel
* I'm probably leaving something out.

I hope that wasn't too convoluted an explanation.

Makes sense. It is a measure of work.
• Posts: 1,502Member Member
I'm pretty sure fitbits with HR monitors are designed to only take your HR into account when it comes to calorie burn when you're in "workout mode" or when its software recognizes that you're working out. That's why it tracks your resting heart rate as a separate category. That's the idea anyways. I'd think if you're just sitting around or doing light housework it wouldn't make much of a difference.
edited June 2016
• Posts: 1,911Member Member
Fascinating info here. Thanks to all adding their knowledge as this is an area I know nothing about.
• Posts: 9,535Member Member
I'm pretty sure fitbits with HR monitors are designed to only take your HR into account when it comes to calorie burn when you're in "workout mode" or when its software recognizes that you're working out. [1] That's why it tracks your resting heart rate as a separate category. That's the idea anyways. [2] I'd think if you're just sitting around or doing light housework it wouldn't make much of a difference.

I'm gonna take these points in reverse order.

2 - You're right. Heart rate monitors are made for tracking cardio exercise and the formulas they use for calories don't really apply to washing the dishes. (Or to lifting weights or maybe to HIIT.)

1 - That's actually not what resting heart rate is, though. You'd think so based on the name. But it's kind of like BMR, the calories you burn just existing without doing anything else. Your RHR is the lowest heart rate you can do, or the one right after you wake up, or after you lay down for 10 minutes, or however you prefer to measure it. There are two reasons this can be useful: it'll go up when you're getting sick or if you've exercised too much and you need a break. Also some zone systems (%HRR) take your resting heart rate into account.
edited June 2016
andrektan wrote: »
However, Fitbit is clearly considering HR in their algorithms. I'm just wondering *why* they're doing that, and if there's any scientific validity to it. I'm guessing they assume that if the user has an elevated HR, they're more heavily active at a given moment?

A lot of things (Fitbits, Garmins, phone apps) factor HR in their calorie algorithms. Generally people consider a calorie estimate more accurate if HR was part of calculating it. But some algorithms are a lot better than others. And even then, sometimes a good algorithm gets put into a system that has some other bug and you wind up with gibberish anyway.

Since you know your weight loss agrees with the numbers before you upgraded, I'd say the old one was more accurate for you.

I agree, but this is why I'm annoyed with Fitbit. It just shouldn't be the case.

I accept that in the end it's all an estimation game, but it's just ridiculous that in my case we're probably looking at a >100% margin of error when HRM functionality is thrown into the mix. It's not like my stats and behavior are some kind of weird edge case.
_Waffle_ wrote: »
The calorie burn in your case (In nearly all scenarios) is simply weight moved x distance. The extra calories, if any, from the heart rate increase is negligible.

I'm gonna agree here. I've done my own little experiences where I've run (attempting as much exactness of each ) the same distance, pace & conditions ) two different runs but one with the HR strap and one without. There's such little difference in the calorie burns it gives me.
andrektan wrote: »
andrektan wrote: »
However, Fitbit is clearly considering HR in their algorithms. I'm just wondering *why* they're doing that, and if there's any scientific validity to it. I'm guessing they assume that if the user has an elevated HR, they're more heavily active at a given moment?

A lot of things (Fitbits, Garmins, phone apps) factor HR in their calorie algorithms. Generally people consider a calorie estimate more accurate if HR was part of calculating it. But some algorithms are a lot better than others. And even then, sometimes a good algorithm gets put into a system that has some other bug and you wind up with gibberish anyway.

Since you know your weight loss agrees with the numbers before you upgraded, I'd say the old one was more accurate for you.

I agree, but this is why I'm annoyed with Fitbit. It just shouldn't be the case.

I accept that in the end it's all an estimation game, but it's just ridiculous that in my case we're probably looking at a >100% margin of error when HRM functionality is thrown into the mix. It's not like my stats and behavior are some kind of weird edge case.

I have a solution for you, but you won't like it .
andrektan wrote: »
andrektan wrote: »
However, Fitbit is clearly considering HR in their algorithms. I'm just wondering *why* they're doing that, and if there's any scientific validity to it. I'm guessing they assume that if the user has an elevated HR, they're more heavily active at a given moment?

A lot of things (Fitbits, Garmins, phone apps) factor HR in their calorie algorithms. Generally people consider a calorie estimate more accurate if HR was part of calculating it. But some algorithms are a lot better than others. And even then, sometimes a good algorithm gets put into a system that has some other bug and you wind up with gibberish anyway.

Since you know your weight loss agrees with the numbers before you upgraded, I'd say the old one was more accurate for you.

I agree, but this is why I'm annoyed with Fitbit. It just shouldn't be the case.

I accept that in the end it's all an estimation game, but it's just ridiculous that in my case we're probably looking at a >100% margin of error when HRM functionality is thrown into the mix. It's not like my stats and behavior are some kind of weird edge case.

I have a solution for you, but you won't like it .

Shut the HRM off?

It's an option I've considered, but there wouldn't be any reason for me to keep the Blaze at that point.

Or do you have a different idea?
• Posts: 853Member Member
I had tachycardia, resting heart rate over 100, when I started now it's in the 60s. I don't burn any less calories now.

It's valid for the monitor to consider the number. Valid in if the same person uses it and their heartrate is the only change that person is likely burning more calories. Where the logic may not make sense is attempting to compare person A with person B.
• Posts: 7,870Member Member
andrektan wrote: »
...but what if HR was the only variable?

Absolutely no difference in calorie expenditure.
• Posts: 479Member Member
andrektan wrote: »
andrektan wrote: »
However, Fitbit is clearly considering HR in their algorithms. I'm just wondering *why* they're doing that, and if there's any scientific validity to it. I'm guessing they assume that if the user has an elevated HR, they're more heavily active at a given moment?

A lot of things (Fitbits, Garmins, phone apps) factor HR in their calorie algorithms. Generally people consider a calorie estimate more accurate if HR was part of calculating it. But some algorithms are a lot better than others. And even then, sometimes a good algorithm gets put into a system that has some other bug and you wind up with gibberish anyway.

Since you know your weight loss agrees with the numbers before you upgraded, I'd say the old one was more accurate for you.

I agree, but this is why I'm annoyed with Fitbit. It just shouldn't be the case.

I accept that in the end it's all an estimation game, but it's just ridiculous that in my case we're probably looking at a >100% margin of error when HRM functionality is thrown into the mix. It's not like my stats and behavior are some kind of weird edge case.

Does the Blaze actually tell you you're burning X amount more calories? Or are you just extrapolating that based on its HR readouts? I honestly feel like all the newer apps and wearables keep increasing the overestimation of calories. Its like vanity sizing, but for calories. A marketing thing.

As to your original question, you're looking at it a bit backwards:
Heartrate and caloric burn relationship - How much does HR actually influence it?
Caloric burn is NOT dependent on HR. HR happens to be an indirect indicator of oxygen usage, so we're able to use it to estimate calories during steady state cardio. It's not even a good measure during intervals or strength training. Definitely not during everyday activities.
• Posts: 2,080Member, Greeter Member
With all the fitness devices these days, as well as all of us who like the data from many sources, it's really surprising that nobody has made some type of real "meter" of HR vs absolute power output and thus calorie burn. I know some devices test VO2max and such, but it seems that if you could also meter power on a Velotron or bike with good meters, then you could more accurately define calorie burn vs HR and differing levels.