Are heart rate monitors trustworthy in calorie burn?

I'm a huge fan of Zumba. It's one of the few exercises I don't dread. I started Zumba about 30 pounds ago, and was burning around 425 calories for a 50 minute class. Now that I've been doing it for a few months and 30 pounds lighter I'm burning around 375 for a 50 minute class. I'm well over 200 lbs. If you use the calorie estimate pre-programmed into MFP, their estimate is way higher than my HRM, so I always use the lower HRM figure because I figure it's more conservative. As one of the other members stated, your intensity can vary based on the instructor and the day. I assume since I've had good results using the HRM, it's better than nothing. I don't eat back all my calories either. I always try to stay under by at least 200 on Zumba days.

If you weighed 225 lbs and ran 6 mph for 60 min that would be almost 1100 calories gross, like HRM would report.

If you use RunnersWorld's formula for net calories expended....

225 x.63 x 6 = 850.50

as a direct result of the exercise.

HRMs vary considerably depending on the algorithm they use. My Garmin 610 is pretty close (it estimated 707 cal for my 5 mile run this morning, using the RW formula around the 600 mark)

ok so i did the walking test and my HRM records 241 but the calculator site records 271.... so there is 11% error. but the HRM calculated less than burned so what does that mean? does that mean at higher heart rate i could be +/- 11% accuracy?

So your HRM isn't aware of the fact you are fitter than your BMI is leading it to believe.
So while your weight may still be higher than healthy range, your fitness level is better than expected.
You are burning more than it knows.
Basically, it sees a low HR and assumes you didn't work hard.
But in reality, you are fit enough your HR doesn't have to go as high to do the hard work.

The upper levels depends on how well you have trained up there.
You might picture it as 2 lines on a graph.
The reality line of best burn up above. And almost straight line going up until you hit anaerobic level.
Your HRM reported line is down 11% below, and it could hold equal distance all the way up, it could come closer, it could drop more.

But as time goes on and you become more fit, more than the weight drops, that 11% will start to widen.
It's easier to get fit faster than to lose weight. In fact the extra weight almost forces it to happen faster.

So was that testing walking speed, or the HR you get with Zumba?
If walking, the higher HR is next one. Then you'll know your line.
How long was the test?

And, as you become more fit - you'll need to retest in a month. Not only for less weight, but more fit, lower HR at same level.
So note your stats.
Next time out you'll try to hit the same HR, and can see your progress in the increased pace or incline required to obtain it again. And the higher calorie burn for that HR.

So if your HRM said you burned 5000 calories in a week down at that level, you know you burned about 550 more, or 78 average more daily. Not too bad.

Correct.

non-steady-state exercise always has some amount of inflated HR until it drops back down by some number of beats. Number and how long it takes depends on your fitness level.

So as you were warming up for your test, you may have been increasing the pace to get to 120 bpm.

And what you'd normally find is you increase it by say 0.5 mph, HR jumps up to 130, and then after a few minutes it lowers back down to 120. So the 120 is what the body needs for that speed. It was inflated by 10 bpm for those few minutes just because of a change in intensity.

Same as when you stopped the treadmill and stood there - did the HR drop back to the normal needed standing HR of say 80 instantly?
No, it took several minutes. So for that entire time it was inflated up to 40 gradually back to none until 80 was hit. Which was all that was truly needed for that intensity.

Now picture your traditional Zumba workout or anything with changing intensities.
HR jumps up above what is really needed for that level of intensity, and just as it's about to lower to where it really needs to be, you change intensity again.
If you went down, it's going to drop - slowly, but really be inflated that whole time. If you went up, it's going to jump higher than it needs to be for however long until it lowers. But then you go and changed intensity again, so it never happens.

So nothing but inflated values during the whole time, and as you can see, some quite big.
In fact probably the worst offender is interval training.
Push really hard and HR reaches max you can get for 15-30 sec, and then you walk. Normally only need say 90 bmp walking, but it never gets down to that level, it gradually decreases and by the time 60 sec of rest is up, it only got down to 120, so inflated the whole time. Since the rest is 4 x the hard part, the avgHR still reads kind of low, but it should have been even lower.

If you could somehow get the real average HR actually needed during your whole routine, then the 11% higher would apply to whatever avg was found and calorie burn given to it.

That's another fun fitness test on treadmill.
After warmup, increase pace by big jump, see what high HR is reached fast, and then how long until it drops back down to a HR it is steady with. How much time to drop and how big a drop - more fit is smaller of both.
Same as when you stop a workout at some high HR, and you stand there, how far does the HR drop in say 1 min, and then 2 min. That's another sign of improved fitness as it drops farther. Some HRM's even do that one for you when you press the stop button.

So the HRM can indeed be very useful. Just not the accurate tool for calorie burn many think it is.
But for your workouts, if you know you are doing the same intensity, you should notice as you get more fit the avgHR for the whole time drops.
Because the HR is able to move faster up, and likely faster down, and lower in general, just showing you have gotten fitter.

As long as you're performing aerobic activity (moderate intensity sustained for long durations, such as joing for jogs) they are pretty accurate. For higher intensity work that spikes the heart rate (such as sprints, weightlifting, or HIIT), though, no.

I'm so damn confused right now after reading all of this. Maybe I should've listened more in maths class or something.

Just go work out

it is interesting that you mentioned HIIT. Even though the HR reading might not be accurate like you said but the workout itself is beneficial for its increase in fat burning and VO2max right?

Of course.

I'm merely discussing a tool and it's limits and uses. Much like people like to talk about their cars.