Fitbit dashboard - rate of calorie burn gets SLOWER the faster my heart rate - WHY?

[mattymoo]

Hi Brain trust,

I've noticed that on my dashboard, on the 'heart rate' tile - the higher my heart rate goes, the LESS calories I am apparently burning per minute.

For example - when my heart rate is at 115 bpm - Fitbit says I am burning 0.9cal/minute, but when my heart rate is at 72bpm, I am burning at 2.5cal/minute.

I'm totally confused! Why on earth would that be the case. I'm worried this is a dumb question, but it just seems strange to me.

If anyone can enlighten me? Thanks!

[Baltoscott]

I assume you are talking about the heart rate and calorie burn graph you get in an exercise record. Can you post a screen-shot, and show us what you are seeing when you compare the two graphs?  

Looking at one of my own records, the patterns of the two graphs are sometimes similar, but out of sync.  Calorie burn goes up before HR does, and then comes back down before HR goes back down.  This makes sense to me and I think it means that the calorie burn/minute has more to do with tracker movement than heart rate.  So, for example, as I increase my effort to move faster the tracker immediately records that motion.  My HR, however, doesn't go up quite as quickly, however, because it takes some time for my muscles to use stored energy and then demand more, which is what causes my breathing, blood flow, and HR to increase.  Then, as I slow down I am immediately burning fewer calories -- which the tracker knows by less movement -- even though it takes my HR a few more minutes to ramp back down.  

Of course sometimes the graphs don't seem to match at all, with HR going up and down and no change at all on the calorie burn graph.  Again, I think it is because calorie burn is mostly determined by tracker movement rather than HR.  Sometimes the HR changes are because of poor readings.  And sometimes tracker movement doesn't reflect all your effort -- for example, if you hold the rails while increasing your speed on a treadmill, your tracker won't pick up all the increased movement because your hand is stationary, but your HR will go up.

This is an interesting thought experiment, I would not get too hung up on it.  Over the course of a day calorie burn and HR readings are pretty accurate, even it it seems kind of odd when you look at short time periods.

[elderwanda]

Weird.  I've been wearing my husband's old Charge2 for a week or two, in addition to my One, and I still haven't been able to make sense of the heart rate information.  Apparently my heart rate doesn't increase at all when I run up the stairs.  Except it clearly does.  

For instance, a few days ago I drove 45 minutes to the gym, did some strenuous weight lifting, and drove home.   The whole time I was actually driving, I was in the cardio zone.  Granted, it was downtown Berkeley, and traffic makes me nervous.   After a few light warm up sets and a few minutes of rest, I looked at my Charge2 and saw my heartrate was 95.  I immediately did six, strenuous barbell squats, and then looked at my heartrate, expecting it to be waaaay up there.  It was 85.   

I think my calories burned matches up with the heartrate, more or less, but it's hard to tell for sure.  So, I did my highest calorie burning of the day while sitting in my car, driving to and from Berkeley.   The time spent under a barbell that weighs almost as much as I do, apparently didn't burn much of anything.  So I guess the lesson is to take it all with a grain of salt.  

[mattymoo]

Thanks so much for your replies - here is a couple of screen shots so you can see what I mean :

[emili]

If you were burning more in fat burn than you do in cardio, that would be a concern. Two calories and 9 beats per minute difference is nothing.. remember that your HR is the average. Lets say in the 104 BPM example, you were actually slightly higher for a period of time and lower for a lesser period of time, but still in fat burn. I am not math person and I am making the numbers up, hopefully it makes sense: Let's say for 30 minutes you were in 125 BPM. You were burning 9 or 10 calories per minute for the entire time. But for 15 minutes you were anywhere between 75-95 BPM. You burned 6 calories per minute.  your average HR would be 104 but you have a slightly higher average calorie burn per minute because of the time spent at 125..all in all the difference is so small, I wouldn't worry about it... 

[mattymoo]

Thanks again for the reply,

I'm not too worried - it just doesn't make sense to me - and yes, it often says that I'm burning LESS calories per hour when I am in cardio or peak zone. Do you think it's a fault?

[SunsetRunner]

Are these the same graphs because they look identical.   Your comment note states average heartrate-so I expected one graph to have a longer lower rate and one with a longer higher rate.   I do see that the red dots are in slightly different places and that would be why the difference.  Do you have graphs of different exercise times that show this as well?