Are these heart rate monitor calories right?

starryphoenix · December 2019

I have a Myzone M3 heart rate monitor that I use at the gym. My stats show I burned around 500 calories. This is a monitor that is around the chest area, so it should be accurate.

I did an hour of cycling with an average of 162 bpm. The bike said I burned around 250, but there were no heart rate tracking on the bike. I just decided to guess my actual calories at 350 because I did some treadmill running before too. The machine said I burned 75 on the treadmill, so I estimated it closer to 50. The bike ended up being 255 calories, so I guessed it as actually around 300 burned. I know the machines can be wrong. I made my estimate higher based on my heart rate monitor’s info.

I’m 5’3 and 175lbs. I’m just wondering if you think my heart rate monitor’s estimate of 500+ calories for my whole workout could be right? It seems to be a pretty good monitor. I’ve just never used one until now, so I have no experience.

AnnPT77 · December 2019

Heart rate monitors measure heart rate.

They then use heart rate, plus statistics from research studies and such, plus any personal data they know about you, to estimate calories.

The closer the activity is to steady state moderate intensity cardio (not intervals, not ultra-intense, limited strength component, more), the more likely the estimate is to be close. The closer you are to average within the population in those research studies, the more likely the estimate is to be close.

If you're a relative beginner, the more likely the estimate is to be on the high side. If you're a very highly conditioned athlete, the more likely the estimate is to be on the low side.

If your heart rate monitor doesn't know an actual exercise-tested personal maximum heart rate for you (you'd know), and if, like a decent-sized minority of people, your actual maximum heart is materially higher than the normal age estimating formulas suggest, the heart rate monitor will tend to overestimate the calories.

So, it's complicated.

Further, most such devices estimate gross calories during the exercise (i.e., they include the calories you'd burn just being alive, doing nothing), when what you really want to put into MFP is net calories (since it already assumes your pre-exercise calories).

I used to be around your weight, although 5'5", and at that point had been quite active for a long time. Based on experience, 500 net calories seems possible, especially if you're not very new to intense exercise, and it was a steady and reasonably intense hour.

No matter what, it's just an estimate based on a value (heart rate) that's only somewhat loosely correlated with calorie burn. Some types of exercise involve fairly accurate metering of energy expenditure (bikes that are properly calibrated and measure watts, for example), so can produce calorie estimates that are likely to be more reliable. Most of the time, exercise estimates are fairly approximate.

The good news is, for most of us the variability is a relatively small percentage of our average daily calories, so we can use the estimates if they're within reason. After 4-6 weeks of calorie counting and using a consistent method of estimating your recurring exercises, you'll have reasonable feedback on whether what you're doing is working well enough to manage your weight loss.

Machka9 · December 2019

I estimate 100 calories for every 5 km ... less if I'm lighter. That seems to match what Strava tells me, more or less. Close enough.

sijomial · December 2019

Heart rate monitor accuracy is accuracy around counting heart beats - not energy.
Your fitness level makes a huge difference to what calorie burns you are capable of. 500 is certainly within the range of possible but that is because the range is so wide.

There's also a huge variability in heart rates including, but not limited to, HR while exercising. An unfit person would tend to have a higher HR burning the same calories as a fit person as that fit person's heart pumps blood more efficiently.

Did the exercise bike tell you your average watts (power) produced?
That's by far the most accurate calorie estimate.
(Average watts for an hour X 3.6 gives net calories.)

How many miles did you run?
(For level ground running bodyweight in pounds X 0.63 X miles run gives a reasonable net calorie estimate.)

starryphoenix · December 2019

This sounds pretty complicated. I’ll just keep under estimating my burned calories to be safe. I’m new to heart rate monitors. Thanks for alll the info! If anyone else has something to say I welcome any info. I love learning about this stuff.

sijomial · December 2019

HRMs can be valuable cardio training aids and it's best to regard them as such.

You can to a degree "calibrate yourself" as regards calorie estimates with a HRM for steady state cardio using the methods I mentioned above but beware that unsuitable exercises such as strength training or even very varied cardio interval training takes their estimates from reasonable (which really is good enough for purpose) to wildly inaccurate.

As you say "I know the machines can be wrong" and that applies to using HRMs for calorie estimates too.
The obverse can also be true - machines can be right and HRMs can be close enough to be reasonable.

If it seems to be good to be true, then it probably is!

liftingbro · December 2019

HRMs are good for tracking effort in workouts but the data collected to calculate calories burned is pretty accurate. However, even if the data going into the calculation is accurate the science the formula is based on is not always accurate.

The fact is that due to metabolic difference between any two people the calorie burn listed on any device could be off by 50%.

That doesn't mean that you can't use the calories burned stats on devices, you absolutely can, it's just about knowing how to use them. The devices will typically count calorie burn pretty consistently. It may be wrong, but it will count it the same way every time for the most part.

The same problem happens with calorie counters like MFP. Not all of the data for foods are correct (not even the USDA info) and again even the calories MFP tells you to eat could be off by 50%. The important part is they are consistent.

You just have to keep in mind that you have to adjust things as you go, for example.

MFP says to eat 2500 calories to maintain weight. You decide to lose weight and it now tells you to eat 2000 calories per day.

Now your HRM says you burned 500 calories, so you eat 500 calories to make up the difference and maintain the 500 calorie deficit that MFP says to use.

You weigh in the first three weeks and lose nothing. Didn't gain either.

Turns out something is off. Could be MFP or your HRM, likely both a little bit.

You stop eating your exercise calories (500 per day), over the next three weeks you lose 3 pounds.

What you find out here is that your metabolism is probably about 25% slower than the average person who's data was used to come up with the formula for calorie burn. (This is assuming 100% accuracy in tracking)

Now going forward you can eyeball it a little better and know that they over-count for you. IMO, the best thing to use these devices for is simply to track workouts and effort in those workouts.

jeraldt6 · February 2020

Regardless, I do appreciate my myzone. I like the instant feedback on my phone when I am out cross country skiing and the instant feedback on the big screens in the gym. I wish there was a myzone group on mfp.

Are these heart rate monitor calories right?

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