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@jimjamslam wrote:I understand and accept that Zone Minutes estimates may vary depending on the workout mode selected (or not selected), as they each use different factors to estimate activity level. But I'm concerned that my heart rate measurements being off when using the Workout mode.
I'm not as understanding as you 🙂... I don't understand why the active zone minutes should depend on the workout mode.
My understanding is that this unit (Charge 5 for me) is supposed to have a heart rate sensor. To me, that means that it should be sensing my heart rate. In other words this should be a directly established number simply reporting what "is".
I've noticed the same as others - if you do the same regular physical exercise routine but just tell the fitbit you're doing a different exercise, then it seems to result in different zones...
BUT from what I observe this is because the reported heart rate was shown in those lower zones during the exercise - I was watching what heart rate it was displaying while exercising.
I try to do the same workout regularly each day, and normally use the "Workout" exercise, and was initially pleased to learn I was doing mostly cardio from this exercise!
But I've dug into the data and can see that the heart rate confidence levels buried in the data export are really poor during this exercise (typically confidence level 0 or 1). But the confidence levels when I'm running or walking tend to be OK (confidence=2). So I tried telling it I was cycling, but did my normal workout.
My heart rate was reported substantially lower - enough to go from allegedly mostly cardio, to now being only a small fraction of it reported as cardio.
This makes no sense.
It totally looks to me as though the Fitbit is taking into account what exercise you tell it you're doing when it tries to get establish your heart rate.
Which is nonsense! A heart rate sensor should be just that - a sensor - it should just report what your heart rate is from what it's seeing.
My understanding is that the heart rate zones should be just that - a measure of how long your heart rate is within a specific zone. This shouldn't make any difference what your associated exercise is - if you heart rate is in that zone, then it's in then zone, and it should be counted in that zone. Irrespective of what's caused your heart rate to be in that zone!
To me, my suspicion is that these units are just so poor at tracking heart rate that, imv, I suspect the fitbit heart sensor algorithm is taking into account what exercise you say you're doing, in order to try and better 'guess' what your heart rate is. Though I'm sure, if pushed, they'd probably phrase it the other way around by saying they're using the information to make it even more accurate 😉
A few BPM out I could understand. But the variation I see makes the difference between my regular workout being mostly cardio (65%+), vs mostly fat burn, with barely 10% cardio.
So I now have no real confidence which is correct. Is my workout giving me a good cardio workout, or only just a good fat burn? I have no confidence at all now as to what I'm achieving.
That's so far different that I question what the point of having the tracker is. At that level of variation I might as well just estimate calorie burn and heart rate zones from average numbers from the web for that type of exercise and just multiply by how long I've been working out. There doesn't seem much point having something getting in the way on my wrist when it gives such a wide variation.
Footnote: Heart Rate Confidence Levels
These are only embedded in the full data export - I haven't found them anywhere on the Fitbit app or website other than in the full data export.
They seem to be either 0, 1, 2, or 3. A confidence level of "0" seems to correlate with "--" shown on the Fitbit when you're exercising.
I have seen examples in my exercises where the confidence level is reported as "2" but the reported heart rate is just not believable - I mean I suspect likely >30 BPM out from what my actual heart rate likely really was at that moment. i.e. it says low end 'fat burn', but in practice in all other places for the same exercise (fast acceleration while cycling) I see it middle of cardio, and that would make far more sense.
I mention this because a confidence level of "2" on a scale or 0...3 might sound pretty good, but clearly it can still be substantially out - just because it claims to be confident, doesn't mean it's anywhere near correct 😊
The following is a plot of my heart rate on my most recent workout, taken from the data recorded using the "Workout" exercise program on the Fitbit and extracted from the data export.
(this is a custom analysis that I've done by quickly hacking together some software to perform an analysis on the fitbit data export - you won't find this view on the app or website)
The colors show the Fitbit unit's confidence level reported for each reading in my exported data.
Red = "0" - this shows "--" on the Fitbit display while exercising.
Orange = "1"
Grey = "2"
Green = "3" - this seems to be the highest confidence value that I've seen it report, so I presume the max.
The "Workout" exercise program for me almost always starts of with "--" on the display and confidence of "0" even if the unit was showing a heart rate on the home screen immediately before hand.
For a fitness tracker that I bought thinking it would give me a reading of my heart rate to better estimate calorie burn, etc, I'm bitterly disappointed. It really seems to struggle - and when even readings with a confidence level of "2" can be quite some way out, seeing much of my exercise recorded as confidence 0 or 1 does not inspire confidence (excuse the pun)!
When the promo videos for the charge 5 show people kick boxing wearing the fitbit, I expected that it would be a lot more robust and accurate tracking heart rate during a workout.
It's also curious how most of the red / zero confidence, tends to occur at the beginning of my work out. The more sweaty I get, and the more I get into the workout, the more confident the fitbit seems to get at measuring my heart rate. Which is at odds with other reports that suggest sweat can cause problems with the readings.
I suspect it's a reflection of how much it's using an 'algorithm' to try to analyse the senor data to arrive at a heart rate reading. Contrary to the impression they give about the great specific wavelength of light sensor, etc i suspect the input signal is very noisy, and they're in essence having to 'guess' half the time, and I suspect this is why they appear to be taking into account the type of exercise you tell it you're doing, and I also suspect there's an awful lot of averaging / smoothing going on.. by that I mean when it's struggling, it is probably looking at what the previous heart rate was when it was more confidence and biasing the current reading towards that, and things like that. .
But if those previous readings weren't all that accurate, then all that does is persist the inaccuracy. And I get the feeling that is happening quite a bit.
All in all, I'm not impressed. I thought the special wavelength HR sensor would have 'seen through' all the motion in your arms, etc. The more I'm seeing, however, the more I get the feeling that the sensor isn't anywhere near as good as they'd like us to believe at seeing the changes in your physiology associate with your pulse, and they're trying to make up for the shortfall algorithmically.
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