HRM overestmating?

honeylissabee · February 2014

I have a Polar H7 HRM that I use with my iPhone to track workout calories.

I've noticed that people say MFP overestimates calorie burn, but I've found that the estimates I get from MFP are usually lower tan what my HRM says I burned.

On Wednesday, I did approximately 25 minutes of a Walk Away the Pounds workout, which I logged as "low impact aerobics." My HRM said I burned 234 calories. MFP estimated 175. (Granted, about 6 minutes or so of the workout WAS jogging, the numbers still don't match up.)

I'm just concerned about this. Is it likely that my HRM is overestimating my calorie burn, or could MFP actually be underestimating for me.

I'm 5'5", female, and weigh around 186 pounds. I also do not exercise regularly, and am not in good physical shape whatsoever. I do get winded and break a sweat fairly easily when working out.

YorriaRaine · February 2014

First things first, a polar heart rate monitor estimates GROSS calories burned, meaning, it includes the calories you would have burned naturally. To figure out net calories, you can either take your bmr and figure out how much you burn per minute or you could use a site like this to figure out the net calories burned.

http://www.shapesense.com/fitness-exercise/calculators/net-versus-gross-calorie-burn-conversion-calculator.aspx

Where it says gross calories burned, put in what the hrm told you.

Secondly, mfp overestimates some and underestimates others, so it is possible you found one that underestimates. Also, the heavier you are, the more calories you burn vs. somebody who is lighter and more fit because your body needs more energy to move around.

As long as your transmitter strap has good contact with your body (meaning you wet it before you put it on), the hrm should be accurate. I will warn you if you have had it for awhile the hrm will start to act a little funky when the battery is about to die. However, those battery's last a good year.

edit: from what I've read, the "funkiness" I was telling you about mostly includes the heart rate monitor consistently losing the transmitter's signal, you will notice when this happens because your hrm will yell at you.

honeylissabee · February 2014

That actually makes sense. I've never heard of that before.

There are two calculators on that site though. I assume to use the first one since it's a lower number.

I've also heard about changing your age on Polar so your Harris Benedict BMR as someone older matches your Miffin BMR which will increase accuracy between the two sites. Is this true?

So, basically, my Miffin BMR at 22 years old is 1605 calories. My Harris BMR if I put my age at 33 is 1606 (34 is 1602), so it will be more accurate if I tell Polar that I'm 33?

Obviously, using BF% will make it even more accurate, but right now, I'm more concerned about my tools (Fitbit/HRM/MFP) matching up as closely as possible.

vorgas · February 2014

I've noticed that people say MFP overestimates calorie burn, but I've found that the estimates I get from MFP are usually lower tan what my HRM says I burned.

MFP is about the least accurate method there is. It can't possibly know all kinds of factors that go into an aerobic calorie burn. MFP is not about being the most accurate. It's about adopting a lifestyle that yields results over the long term. For example, if you are hitting the elliptical for 30 minutes, MFP will always give you the same number. Doesn't matter whether you are doing 50 strides a minute or 200. Doesn't matter if the resistance is on 1 or 20. Doesn't matter if the elevation is flat or highly inclined. MFP will only be accurate by accident. If accuracy is your principal concern, only use MFPs numbers as a last resort. For the 50 strides a minute crowd, MFP likely over estimates. For the 200 strides a minute group, MFP under estimates.

On Wednesday, I did approximately 25 minutes of a Walk Away the Pounds workout, which I logged as "low impact aerobics." My HRM said I burned 234 calories. MFP estimated 175. (Granted, about 6 minutes or so of the workout WAS jogging, the numbers still don't match up.)

So you told MFP you did an exercise, which you didn't actually do, and it gave you a different number than your HRM? And if you were just simply walking, you probably spent most of the time below the aerobic threshold, so your HRM won't be accurate anyway.

I'm just concerned about this. Is it likely that my HRM is overestimating my calorie burn, or could MFP actually be underestimating for me.

Using a HRM is more accurate, but if you don't know your VO2 Max, and using that to calculate it, it will be off as well. Plus, a HRM is only accurate in the aerobic zone. Once your HR climbs above 65% Max, it begins to skew as your body begins utilizing more and more glycogen as fuel. And, if you have anything that is adjusting your HR (caffeine, workout supplements, thermogenic boosters, diet pills, etc), it can be off as well. Remember that a HRM only measures your heart rate. It doesn't measure caloric consumption. That is a calculation based on your heart rate, while it is in the aerobic zone. Too high or too low, or if you're doing anaerobic exercises (such as weight lifting), and it is no longer accurate.

So, basically, my Miffin BMR at 22 years old is 1605 calories. My Harris BMR if I put my age at 33 is 1606 (34 is 1602), so it will be more accurate if I tell Polar that I'm 33?

Both of these calculate your BMR and don't really have a significant effect on the calories burned during exercise. Fiddling with the age to get a number that you want to see is just a math problem, and isn't going to give you more accurate info.

Obviously, using BF% will make it even more accurate, but right now, I'm more concerned about my tools (Fitbit/HRM/MFP) matching up as closely as possible.

You will drive yourself crazy trying to get all of these tools to match up the same. They all use different formulas, and different methodologies to get their numbers. And most of them don't tell you what they use. And their numbers can change based on your effort.

Can a fitbit strapped to your arm possibly give you an accurate measurement on a bike ride? Can it tell the exertion level required to pedal 80 strokes a minute uphill vs flat land vs down hill? Can it tell the difference if you're jogging uphill?

Save your sanity. Pick a method and stick with it.

Bottom line, I bet you'll find most of these only vary by about 100 calories on any given day. If 100 calories is going to make the difference between whether or not you're losing weight, you're doing it wrong

maggieobc · February 2014

I appreciate this rundown, vorgas.

jasonpclement · February 2014

I've done a pretty large amount of HRM work. And judging from the stats you gave in your original post, I think what you saw we probably pretty accurate.

One thing to watch out for is when your HRM says your heart rate is super high for a period of time, you kind of just have to know its wrong, and that you may get a bit of an overestimate. They usually correct themselves after a minute or so.

Example: I went for a run w/ my wife, and about 2 minutes into the run my heart rate showed 170, however I was only running a very moderate pace. The monitor tapered down to 140 after a minute or two. I know for me, 170 means I am working extremely hard at a pace that I probably can't sustain for a real long time. A moderate pace for me is always somewhere between 140 and 150.

After enough workouts with your HRM, you'll get pretty comfortable just knowing your body's response to exercise.

Dellie1989 · February 2014

BUMP-ing into my topics

GetSoda · February 2014

The only thing a HRM is reasonably good at guessing is the time.

YorriaRaine · February 2014

There are two calculators on that site though. I assume to use the first one since it's a lower number.

Use the first one. Note that the first one says "gross to net" calc. While the other says "net to gross."

You already have the gross, you want the net

honeylissabee · February 2014

I'm going to be replying out of order, so bear with me.

Jason- I have noticed the occasional false spike, but I've also noticed the occasional moment where it isn't registering any activity whatsoever, so I generally don't worry about it.

Vorgas- Since 6 out of 25 minutes was higher impact aerobics (Walk Away the Pounds is NOT just walking), I decided to test calculating 19 minutes of low impact aerobics and 6 minutes of high impact to see if the numbers were closer to my HRM. My concern with the BMR with the HRM is that I know based on past calculations (though none in the past 2-3 months) that my BMR if using a formula involving body fat percentage is actually lower than what MFP says my BMR is (and my understanding is that Polar uses the Harris method which give me an even HIGHER BMR) which means both could be overestimating a little.

My activity level varies fairly drastically from day to day, and most of that is NOT though purposeful exercise. I do not have a normal routine, so I like using my Fitbit to monitor my activity. When I enter in my workouts onto MFP, I put in the time I started and the duration of the workout, and it overrides what Fitbit thought I burned during that period of time.

Based on my current body fat percentage (using an Ormron Fat Loss Monitor), my BMR is 1,489. Based on being sedentary, that means I burn approximately 1,786 calories a day. MFP estimates that I burn closer to 2,020 per day. That difference is nearly half a pound a week.

I know I can manually enter my own calorie goals on here, but I am trying to figure out how to tweak my other devices so things line up as closely as possible. Is changing my age on Fitbit so my Miffin BMR as a 48 year old matches my Katch BMR actually going to work to get things at least somewhat close?

Buddhasmiracle · February 2014

I've noticed that people say MFP overestimates calorie burn, but I've found that the estimates I get from MFP are usually lower tan what my HRM says I burned.

MFP is about the least accurate method there is. It can't possibly know all kinds of factors that go into an aerobic calorie burn. MFP is not about being the most accurate. It's about adopting a lifestyle that yields results over the long term. For example, if you are hitting the elliptical for 30 minutes, MFP will always give you the same number. Doesn't matter whether you are doing 50 strides a minute or 200. Doesn't matter if the resistance is on 1 or 20. Doesn't matter if the elevation is flat or highly inclined. MFP will only be accurate by accident. If accuracy is your principal concern, only use MFPs numbers as a last resort. For the 50 strides a minute crowd, MFP likely over estimates. For the 200 strides a minute group, MFP under estimates.

On Wednesday, I did approximately 25 minutes of a Walk Away the Pounds workout, which I logged as "low impact aerobics." My HRM said I burned 234 calories. MFP estimated 175. (Granted, about 6 minutes or so of the workout WAS jogging, the numbers still don't match up.)

So you told MFP you did an exercise, which you didn't actually do, and it gave you a different number than your HRM? And if you were just simply walking, you probably spent most of the time below the aerobic threshold, so your HRM won't be accurate anyway.

I'm just concerned about this. Is it likely that my HRM is overestimating my calorie burn, or could MFP actually be underestimating for me.

Using a HRM is more accurate, but if you don't know your VO2 Max, and using that to calculate it, it will be off as well. Plus, a HRM is only accurate in the aerobic zone. Once your HR climbs above 65% Max, it begins to skew as your body begins utilizing more and more glycogen as fuel. And, if you have anything that is adjusting your HR (caffeine, workout supplements, thermogenic boosters, diet pills, etc), it can be off as well. Remember that a HRM only measures your heart rate. It doesn't measure caloric consumption. That is a calculation based on your heart rate, while it is in the aerobic zone. Too high or too low, or if you're doing anaerobic exercises (such as weight lifting), and it is no longer accurate.

So, basically, my Miffin BMR at 22 years old is 1605 calories. My Harris BMR if I put my age at 33 is 1606 (34 is 1602), so it will be more accurate if I tell Polar that I'm 33?

Both of these calculate your BMR and don't really have a significant effect on the calories burned during exercise. Fiddling with the age to get a number that you want to see is just a math problem, and isn't going to give you more accurate info.

Obviously, using BF% will make it even more accurate, but right now, I'm more concerned about my tools (Fitbit/HRM/MFP) matching up as closely as possible.

You will drive yourself crazy trying to get all of these tools to match up the same. They all use different formulas, and different methodologies to get their numbers. And most of them don't tell you what they use. And their numbers can change based on your effort.

Can a fitbit strapped to your arm possibly give you an accurate measurement on a bike ride? Can it tell the exertion level required to pedal 80 strokes a minute uphill vs flat land vs down hill? Can it tell the difference if you're jogging uphill?

Save your sanity. Pick a method and stick with it.

Bottom line, I bet you'll find most of these only vary by about 100 calories on any given day. If 100 calories is going to make the difference between whether or not you're losing weight, you're doing it wrong

All the above, and the last paragraph best describe my use of a polar FT6 and MFP for cycling -- about 100 cals difference (MFP more)

TAsunder · February 2014

For a 60 minute run the difference for me is usually at least 200 calories between what my HRM or any app attached to the HRM reports compared to MFP, depending on my level of exertion.

RoseGoldDinosaur · February 2014

My Polar HRM was always very close to the MFP guesstimate of how many calories I burned. Usually my HRM was over about 50 calories for a 30 minute workout and 100 calories for an hour. (Maybe this is that gross calorie thing people are mentioning?) My new HRM is saying I burn more, although I don't think it's giving an accurate reading. One of the best reasons to wear a HRM is motivation. It doesn't always matter if the reading is accurate as much as it matters wether it says you burned more than yesterday. I find myself pushing to get my heart rate up and keeping it there because of the HRM and I think that's the main goal. In the end I prefer MFP numbers because they are lower it's better to underestimate than overestimate. Hope that helps!

HRM overestmating?

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