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The Real Facts about HRMs and Calories -- What you need to know before purchasing an HRM (or using one)

Every week, there are at least a dozen questions about heart rate monitors--which model to buy, what the numbers mean, how the calories compare to readings from machines, etc. I have answered these questions numerous times, but wanted to go into more detail for those who are interested.

HRMs can be great training tools. I have used various types of heart rate monitoring for my training for over 20 years. I currently have a Polar F11 (edit: I now use an FT60--the F11 went to Polar heaven about a year ago), although I don't use most of the features. About 10-15 years ago, Polar introduced their "OwnCal" feature--using heart rate to estimate calories burned during exercise.

This has proven to be extremely popular and has really driven the sale of HRMs. Now virtually every manufacturer includes some type of calorie-counting feature with their HRMs. Effective marketing has created the following beliefs about HRMs and calories:

1.HRMs directly "measure" caloric expenditure. 

2. HRMs are the most accurate way to measure calorie expenditure during exercise.  

3. All HRMs have the same level of accuracy when counting calories. .

4. HRMs can be used to accurately count calories expended during strength training and during rest and 24-hour activity periods. 

5. HRMs are always more accurate than the readout from exercise machines.  

6. If your heart rate response becomes lower when doing a certain activity, it means you are burning fewer calories.  

None of these are true.  HRMs only indirectly estimate calories expended during certain types of exercise. Unless they are set up properly and the profile information updated regularly, they can have significant inaccuracies. And not all HRMs are the same. 

Let's look at all of these:

HRM Theory

First of all--how do HRMs count calories? First thing is that HRMs do NOT measure caloric expenditure--neither directly nor indirectly. HRMs measure heart rate and that's it. They estimate caloric expenditure during steady-state cardiovascular exercise using the relationship between heart rate and oxygen uptake (or VO2).  

The most commonly accepted method for measuring the calories burned for a particular activity is to measure oxygen uptake (VO2). 

During *steady-state*, aerobic exercise, oxygen is utilized at a relatively consistent rate depending on the intensity of the exercise. There is an observable and reproducible relationship between heart rate and oxygen uptake.When workload intensity increases, heart rate increases and vice versa. 

If we have some individual data--resting heart rate, maximum heart rate, VO2 max, weight--it is possible to make reasonably accurate estimates of caloric expenditure based on the percentage of HRmax or percentage of HRreserve at which someone is working.

For example, we know that 70% of HRmax is equivalent to approx 57% of VO2max. If we know that person's VO2 max is 12 METs and they are working at 70% of HRmax, we can estimate that they are working at (57% x 12 METS) or 6.8 METs. If that person weighs 80 kg, we can estimate that they are burning ~545 Cals/hour (MET value x Body wt in kg). 

The major HRM manufacturers (Polar and Suunto) use much more sophisticated sensing technology and algorithms, but they are still based on the same basic principle--the association of HR to oxygen uptake.  

So, it must be emphasized again: HRMs calorie counts are only accurate when there is a consistent and measurable relationship between heart rate and oxygen uptake.  That means exercises and exercise movements that are aerobic in nature and that are performed at intensities between 40% of VO2 max and the lactate threshold

There are a number of conditions under which heart rate can increase, but without an increase in oxygen uptake:

-Stress, Illness

-Dehydration

-Environment (high heat and humidity)

-Heavy strength training (HR increases because of increased pressure)

-Changes in posture

-Cardiovascular drift during extended aerobic exercise

In other conditions--arm work, overhead work, "anaerobic" or sprint exercise--an HR increase will reflect in increase in VO2, but it is not a consistently measurable and reproducible relationship, therefore the HRM calorie count is not as accurate. 

Note: Certain higher-end HRMs--the Polar RS800 and Suunto T6c use a very sophisticated method of analyzing the R-R interval of heart beat signals. When using this method, it is claimed that they can more accurately estimate caloric expenditure at rest, during anaerobic exercise and even during post-exercise oxygen consumption. Since these models are in the $350-$400 range, I am not including them in this review--if you are interested in more detail, check out www.firstbeattechnologies.com and www.suunto.com

HRM Setup 

Even if you have purchased a quality HRM, the readings will only be as good as your setup information. An accurate estimation of caloric expenditure requires the following input:

Resting heart rate (HR rest)

Maximum heart rate (HR max)

VO2 max

Weight

Age

Gender

Not only must this data be accurate when you set up the HRM, it must be updated as well if your fitness level increases or if your weight decreases.

Determining  HR max and VO2 max are the most difficult tasks. You can use a prediction formula (e.g. 220-age) or the built-in "fitness test" of a Polar, but these have a not insubstantial standard of error. For HR max, I would recommend that you Google the web for various predicted HR max fornulae and determine a range of possibilities. Then compare your exercise heart rate to your feelings of perceived exertion. If your HRM shows your HR during exercise is 90+% of maximum, but you feel like you are cruising at an easy effort, your HR max is probably higher than the predicted number. 

VO2 max is even trickier. You can try some field tests (1-mile run, Cooper 12-min run) or a submax fitness test protocol programmed into a treadmill  (if there is one) if you have the ability or access. 

Keep in mind that as you continue to exercise, it is likely that you will lose weight and that your cardiovascular fitness level will improve (that's the whole point, right?). When that happens, you need to adjust the VO2 number up and the weight number down in your setup.

Choosing an HRM 

The first thing you must do is determine what features are important to you.

Accurate heart rate measuring

Accurate (as possible) caloric estimation 

Exercise planning or "coaching"

Stopwatch features

 Data storage/transfer/analysis

If you are primarily interested in heart rate monitoring and basic stopwatch functions, then many different brands and models will probably fill your needs.

However, if you want the most accurate caloric estimation, there are significant differences between brands and models.

Just because an HRM provides a calorie count doesn't mean that number is any more accurate than one from a machine or even a number you just made up. Manufacturers know this feature is popular--some will stick any old number on the display to make you think you are "measuring" calories. 

For greatest calorie count accuracy, an HRM must have the following features:

1. Chest strap sensor for continuous monitoring

2. Ability to manually input HR max, VO2 max, gender, age weight and HR rest.

3. Sophisticated analysis technology and software which has been validated on large numbers of test subjects.

For those features, your choices are going to be limited and you cannot go super-cheap. If you cannot enter VO2 max, then the HRM is using a more general format to determine your fitness level, which means greater inaccuracy.

Note: The only HRMs I know that meet the above criteria are the Sunnto T-series HRMs, the older Polar F6 and F11 models, and the newer Polar FT40 and FT60 models. FT4 and FT7 do not. Suunto does not use VO2 max, but they have a detailed series of "activity levels" that accomplish the same thing. They may not be the only ones, but they are the only ones I can say with certainty. I have looked at the owner manuals of other brands (Timex, Sportsline, Mio) and they do not allow manual VO2 input. Don't know about Reebok or Nike products. 

 Note #2 Update: Someone in the comments suggests that the Garmin Forerunner 405 also uses Firstbeat Technology software, which means they might also use R-R analysis--worth checking out. 

So I bought a cheapie, now what? 

Well, it's not a complete waste--but you do have to be careful about how you include those calories in your overall eating and exercise plan.

Even if the HRM uses a less accurate method of determining your caloric expenditure, the relative changes in the numbers should give you some insight. Calories are a measure of total aerobic work performed. If you do 30 minutes on a cross trainer and burn "300" calories for example with an avg HR of 130, then 3 weeks later burn  "330" calories on the same machine in the same amount of time at the same average HR, that represents a significant increase in your aerobic work capacity and probably a similar percentage increase in the caloric expenditure. You can use the relative numbers to gauge your progress for different machines or activities. 

I hope this is helpful. 

 UPDATE SEPTEMBER 2011: Looking at updated manuals for the most commonly used Polar models (FT4, FT7, FT40, FT60), I think I have a better idea of the product features. 

The FT4 and FT7 models do NOT allow manual entry of VO2 max and do not include the Polar "fitness test" feature--at least I did not see it mentioned in the manuals. I don't know how they assign a "fitness level" or how the HRM takes into account changes in your fitness level over time.

 The FT40 and FT60 DO allow manual entry of VO2max, plus they have fitness tests included. One of the tests uses your setup info, resting HR and a description of your physical activity status to estimate VO2 max. I have seen this formula described elsewhere and it is probably adequate if you don't know your VO2max. If you ramp up your exercise program or notice improvement, these features should be able to capture that improvement and reflect that in your calorie estimates.  

209 votes + -

77 comments:

SraArroz wrote 108 months ago:
Thank you for taking the time to put all of that on here! I'm saving it for reference! =)
kelly_a wrote 108 months ago:
thanks for clarifying this, and clearly understood!
mama22girlz wrote 108 months ago:
I'm thinking about getting a HRM so thanks for the info. I'll save it to refer to it once I decide on if I'm buying one or not.
marioh wrote 108 months ago:
Tank you for explaining. I’m using a Garmin ForeRunner 405cx that is using this method for energy expenditure estimation http://www.firstbeattechnologies.com/files/Energy_Expenditure_Estimation.pdf

Don’t know if it is accurate, but HRM and calories burning is a motivation to go running when I look at my calories daily goal !
BTW, MFP is very very useful.
Tanks.
jmarie9 wrote 108 months ago:
thanks so much. im gonna save this as well for when i want to purchase a HRM.
TnTHawkins wrote 108 months ago:
Thank you for the info. I just got the Garmin ForeRunner 305 and love it for the money. I still go by the MFP burned calories and mostly use it for the GPS functions for distance and pace. The HRM is a bonus to see if my heart rate for training. I also have the Garmin Edge 305 for the bike. I have really good luck with Garmin products and you should check them out.

Again thanks for the info,

Todd
fooja wrote 108 months ago:
thanks for the info!!
itsjustkeiah wrote 108 months ago:
I am new to MFP, and had seen many postings about HRMs and knew nothing about how to use one. I was actually about to do a search on the topic when I saw this post! Thank you, thank you, thank you!!! Very clear.
Roger_Williams wrote 108 months ago:
I've only recently felt compelled to count calories and exercise, and frankly I had never heard of HRMs. I appreciate the introduction and, as a physics major who did some research on monitoring instruments, I recognize the value of the points you make. Too many people believe that just because a device displays a number the number is accurate and meaningful. It just isn't so! Thank you. I don't think my current level of interest justifies purchasing an HRM but at least I can make an informed choice if and when I decide to do so.
quickchica wrote 108 months ago:
I really enjoyed the info, I'm a geek that way. I've had a few Polars through the years and my latest is the RS300. I really like it but recently having trouble with the accuracy. For instance, going up a hill and says I'm at 47 beats ( I'm not Lance). So, I guess I want people to know that going by "how" you feel is the best bet. I have literally soaked the strap to get a read out, I didn't use to have to do that. I did notice the calorie count is lower than the treadmill which allows me to work a little longer.
SimonLondon wrote 108 months ago:
I have a feeling you'll be linking to this a lot :)

You really are a very helpful person!
SHBoss1673 wrote 108 months ago:
Fantastic Adzak! Love it! Nice work. Thanks for putting in the effort.
maurierose wrote 107 months ago:
Thanks Adzak! I always enjoy reading your educated info.... sure makes a lot of sense. :o)
bslclay wrote 106 months ago:
This was very helpful! Thank you!
SillySkittles wrote 104 months ago:
Thanks for taking the time for this! I definitely learning the technicalities behind the "calories" burned as I was also beginning to doubt the accuracy of my HRM as there was a significant difference between the output it was giving me and the output the machine was giving me. But your explanation and emphasis on VO2 max helped with that. I have the Polar RS100 which I was told was more specific to runners, but I will definitely be more conservative when I consider the outputs. Thanks again!
IsMollyReallyHungry wrote 101 months ago:
Thanks!
kianaik wrote 99 months ago:
Thanks for the info! Do you know if the Polar F6 has these minimal features that you mentioned?
skygoddess86 wrote 98 months ago:
Thank you this helped a lot.
bubblie117 wrote 97 months ago:
Very informative, thanks!
momof7withchrist wrote 96 months ago:
Thank you so much. Not feeling so overwhelmed now!
momof7withchrist wrote 96 months ago:
Thank you so much. Not feeling so overwhelmed now!
kswizzy wrote 95 months ago:
loving this!
fouchou09 wrote 95 months ago:
Great explanation! Really helpful and easy to understand.
waverly9876 wrote 95 months ago:
Thank you! Im still confused but that really helped
jen_marie81 wrote 95 months ago:
Thanks so much for taking the time to do this... It has really helped!!
McKayMachina wrote 95 months ago:
AMAZINGLY helpful information. Thank you so much! I've had my eye on the Polar F6. Looks like I'm sticking with it. Thx! :)
TrainerRobin wrote 94 months ago:
Thanks for recapping this info in one spot. I'm answering this question all the time, and your post will make it much easier for me. Your post is almost an exact match to a paper I wrote about a year go. Nice work! :)
irishgal44 wrote 94 months ago:
Love it! And as I have experienced, my hrm helped me discover I have a sinus tachycardia. And due to this, cals burned on my hrm are inaccurate. They read too high due to such a high hr. But I still love mine because I know to slow down when my heart is working too hard. It is a true lifesaver for me!
amandalc980 wrote 94 months ago:
Wish I had read this before buying the FT4. If it breaks I will be looking to you for recommondations. :)
Flyntiggr wrote 94 months ago:
The Garmin 405cx does utilize the first-beat technology. You enter activity level, similar to the Suunto. I've had a 405cx for 10 months, and it is on its way back to REI. Garmin pushed a software update, and totally screwed up the watch. Went from working perfectly to barely staying charged. I've been all over the Garmin forums, and it is a known issue with no definite fix. I ordered a Suunto.
streko3a wrote 93 months ago:
Thanks for the article! Do you know what would the error be in the calories burnt predictions by these HRM that you've recommended?
tiaydew wrote 93 months ago:
This was so informative! I just got my HRM and was checking for tips to make sure I'd set it up correctly.
Jennical wrote 92 months ago:
Thanks for sharing this.. I need to read this again when I have my HRM with me...
JenL0690 wrote 92 months ago:
Thx so much for the info!!
LC28 wrote 92 months ago:
Thank you. Great information.
MissMaryMac33 wrote 92 months ago:
Great information as I've been having a terrible time finding an HRM that seems to work. I went with your suggestion and got a Polar FT7 (you said F6 or higher) but I can't find anything in the manual at all about setting my Vo2 so now I think I bought another one that's not going to do what I need. This is the 5th one I've tried this week and I'm seriously frustrated!
tarapin wrote 91 months ago:
Amazing and concise explanation.....THANK YOU!!!!
efriling wrote 89 months ago:
Thank you so much for the explanation, detailed but consise....perfect!
SmartFunGorgeous wrote 87 months ago:
I wish I'd seen this before wasting money on my HRM, but when I buy my next one, I will reference this for sure!
dad106 wrote 86 months ago:
I just bought an FT60.. Had an FT7 since April, which I love but I figured it was time to take the leap!

Thanks for all the info!
kellyyjean wrote 86 months ago:
Thank you!
andrejjorje wrote 86 months ago:
Should definitely be a sticky,.
fitnessbudget wrote 85 months ago:
I saving to buy a Polar FT60...so this is very helpful and confirming information. Blessings!!!
FittingIn wrote 85 months ago:
I just had a LivePerson chat with Polar. They said that the FT40 is the least expensive model that has the VO2 manual entry feature.
Gracestar12 wrote 85 months ago:
great explanations : )
slyder432 wrote 84 months ago:
thanks for the info!
Takes2long wrote 84 months ago:
Thanks! I'll have to re-read this again!!
Chuckempire wrote 84 months ago:
Great article!
change_happens wrote 84 months ago:
thanks
tbskipp wrote 83 months ago:
My head is still spinning. Thanks for the info!
JeninBelgium wrote 83 months ago:
Thank you very much for the posting and the time and energy you put into it.

I have an old Polar F11 and a new(er) Garmin 610- I can confirm that the the Garmin 610 uses first beat technology- however, I have the "gut feeling" that the polar is better for my cardio training (improvement) than the Garmin- - the polars various training programs etc are really focused on improving cardiovascular/aerobics endurance etc
that being said, Garmin gives me a much lower calorie count- thus, knowing my luck, it is probably more accurate :-) I like to use my polar indoors and my garmin outdoors (since I bought it for the GPS functionality)
katg73 wrote 76 months ago:
Wow, this is very helpful! I was really close to purchasing the Polar FT7, but after reading this (and of course wanting the most accurate calorie count), I may need to invest in the FT40. Definitely need to save this. Thanks again!
swagnificent3 wrote 72 months ago:
Awesome! Thanks for the information. I was looking into several different Polar models with FT4 and 7 being on the list as well as FT40, 60 and 80. Having a little bit more knowledge of the differences and what they offer I can cross off 2 off top and focus on the other 3 now.
Salvaje26 wrote 72 months ago:
Thanks! Getting an ft40 or 60! Very helpful!
workitoffnow wrote 70 months ago:
Will the FT40 and FT60 allow you to measure calorie count at rest? Or is it still only good for exercise?
sbrownallison wrote 65 months ago:
I just found this blog and want to read it when I have time! Good stuff!
Anonymous wrote 63 months ago:
I've been doing weight training on and off for quite a few years now, but have only recently began to realize that an HRM is an absolute need. Also I'm a bit of a snob (as an electrical engineer and product design engineer) when it comes to the "display" that I see on virtually any device.

Display technology has come a very long way beginning about 2010, there are many displays which are very readable, sunlight visible, and low power to boot. Yet as I'm looking over what is available to me to buy for a HRM, I feel like I'm about to purchase a 1985 Casio LCD calculator watch!! I don't see any of these as having a decent display!

Can you point me to one HRM device that is "state-of-the-art" when it comes to the display? When I'm working out, I want to see my heart rate indoors or outdoors, in the gym, out on the grass with my kettle bells, or on my bike, and ALWAYS on my wrist... and in big readable bright numbers... not cheesy gray dots too small to read or washed out from sunlight.

I'm about to plunk down hundreds of dollars for a device which may not be readable? Why? I want an HRM, I really do... but don't want a POS display.
Anonymous wrote 62 months ago:
Recently, an online friend that is a exercise physiologist posted this website to calculate vo2max. Maybe it will be useful.
http://www.ntnu.edu/cerg/vo2max
Anonymous wrote 60 months ago:
I just purchased the Polar FT60 HRM and have successfully programmed it to measure my calorie burn after each workout. I'm very fit, 58, female, but am plagued by one condition: NO HRM of any model (whether in watch form or exercise machine) can give me an accurate reading on my heart rate. I have some kind of electrical field that makes the device swing WILDLY from a heart rate of 60-odd to over 250. Even with the Polar FT60, about 1/3 of my workout produces these wild gyrations. As a result, the HRM shows I am burning close to 700 calories per session, when it's actually more like 350. Any advice for me?
Anonymous wrote 60 months ago:
Check that it is not due to static charge generated by your clothing.
Anonymous wrote 53 months ago:
Thanks for the info.
Freeborn111 wrote 52 months ago:
Now I just feel discouraged about my recently purchased Polar FT7 HRM.
cpkoala wrote 51 months ago:
Love this article. Very helpful. Would love more info on Garmin's as well.
dalogan72 wrote 50 months ago:
Thanks for the article. Excellent.
Berry1301 wrote 49 months ago:
Hi, Do you know if is possible enter this information to customize my HRM polar H6 in any app??
Resting heart rate (HR rest)
Maximum heart rate (HR max)
VO2 max
Weight
Age
Gender

Thank You
Anonymous wrote 46 months ago:
Can you help me with the percentage of accuracy Polar ft4 gives? I have already bought it, please tell me to what extent it is accurate so that I can keep my diet plan according to it.
Anonymous wrote 46 months ago:
Does that mean that the calculations for accurate calorie burning could be done by an app with the right formula ?

From what I can gather counting the heart rate is reasonably accurate with many monitors.

Are there any apps around that could be used for accurately doing the conversions that you know of ?
frank
jequirity wrote 39 months ago:
Thank you so much for your easy to understand explanation on this confusing subject.
Wallybanger wrote 39 months ago:
Good write up. Wish I had read it before buying a Wahoo Tickr. It seems ok but the software isn't great and you can't enter V02Max.
Anonymous wrote 32 months ago:
Another thanks , so many of us are Internet takers , kudos to the givers..... repeat the sentiment know the underlying science that you have adopted in your life... help sift out better gear by understanding its method of calculation.Adrian D
Anonymous wrote 32 months ago:
Thank you for the article. I was using a Garmin 310 xt which went to Garmin heaven. I then switched to a Garmin 910 xt and have sent returned it. The calorie count showed 290 calories burned in an 85 minutes road bike ride averaging heart rate of 130 and I'm 65 years! NO way it was accurate and Garmin was not helpful. Thanks and now I will check others out.
baramstead wrote 28 months ago:
Very informative! Thank you!
Anonymous wrote 23 months ago:
There is no fitness tracker or exercise machine out there that is 100% accurate. So I tell my clients, whatever the machine says, take 60% of it. If your goal is weight loss, you want to UNDER estimate what you burn and OVER estimate what you eat.

Louben,
repkefitness.com/
Anonymous wrote 20 months ago:
If you have access to a Concept2 Rower, many gyms have them, you can find out VO2 max by doing a 2000m max row. Concept 2 has a VO2 calculator on their website. Might want to watch a few videos to make sure you have decent technique, it would throw you off.
Anonymous wrote 19 months ago:
Thank you! Very helpful.
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