Heart Rate , measuring or calculating ?

[NirMoshe]

i am facing wierd behavior with the HR value , befor starting workout my HR is ~55 then i am starting workout on the watch (ionic) before even starting to move my HR jump to 70-80 , next step im doing little warmup and the watch presenting HR 120-140 

just to understand the numbers, i am 37 years old and my resting HR is 47 , max HR is 183

so 120-140 is way too much for warmup .

next test was to take another ionic from my friend and put it on the second hand , 

on one of them i started workout and on the second one i didnt , there was a 20 bpm different betweed them 

so my question is : is the HR calculating or measuring ? 

if its measuring its supposed to present the same HR on both of the watches 

if its calculating its not the real HR 

[bmw54]

Measuring or calculating? that's the same issue I faced within weeks of using my Ionic - only my question was of distance and pace. It seemed inconceivable that a GPS device wouldn't use GPS to measure distance. Yet that has proven to be true.

Your observations are even stranger. Yet they're plausible and might explain the differences between HR as measured by my fitbit Surge and the Ionic. (Surge has measured average HR 30 points lower than the Ionic during extended, somewhat equal effort, training runs.) At age 63, the Ionic's measuring my HR at a steady range above 190. 

[SunsetRunner]

I'm your age, similar RHR. So the HR is measured using photoplethysmography. However, I don't trust HR measuring at all. Simply, because the technology, first of all, doesn't measure HR ( and I mean here all the devices, not just Fitbit ones ). It measures blood flow - that's something little bit different and there is a number of conditions that may affect the output ( I remember some trackers . The calculating probably happens when for some period of times the tracker isn't able to read HR, this was happening to me when I was wearing Charge 2 before ). I remember Fitbit was quite proud of the technology including estimating the HR when readings aren't available.

In my case ( I wrote it many times ) HR is very off. Here's an example from Yesterday morning:

178bpm vs 154bpm. 24 beats of difference, this is the whole different HR zone. I checked it with the sensor on my phone too but bit too late and didn't take the screenshot but the result was closer to the cardio machine ( but already lower due to cooling down ). Do I trust the cardio machine? Not quite, but more than optical measurement for two reasons - different technology and reading from two data inputs rather than one ( two thumbs ). While resting HR is more or less accurate, during exercise it's good to have alternative ways of checking HR. This quite visibly affects the number of calories burnt ( I burn a daily lot more than Fitbit thinks which usually is reflected in my weight going down ). What I'm saying is that you have to learn to make the best use of those readings but mind it's only a hint rather than 100% accurate data.

Answering to your question, HR is measured when you're wearing the tracker but calculated ( probably, somebody corrects me if I'm wrong but I've seen such behaviour before in Charge 2 ) when the sensor cannot get the measurement.

[NirMoshe]

so just to understand , if the HR is not accurate and all the calories and HR Zones based on this HR so all the detailes that i see in my watch is not accurate .... so why the hell do i need this watch ??

its even not consistency 

[SunsetRunner]

@NirMoshe that's a very good question that I was asking myself too. The thing is once you realize how off the HR and calories count can be you may ( or may not 😉 ) learn to adjust it. It's still a useful piece of information especially during the days when you're less active. I find those readings more accurate then ( so that they pretty much match pulse oximeter reading and other devices ). Unfortunately, during exercise, the readings are incredibly off in my case. I sort of learnt to adjust that but it requires me to follow a certain pattern and use other tools like Trendweight ( logging weight daily, logging each food etc. ). I'm considering getting a chest strap which is way way more accurate ( due to using technology similar to the one used in the ECG examination ) but Fitbit app isn't able to work with any external sensor.

[bmw54]

Fortunately for me HR is not part of my training strategy. However, my actual HR occasionally spikes into a zone that leads to physical and mental shut-down - especially during the hotter months of summer. The Ionic is telling me that I am, basically, always approaching that zone: 200+ bpm's.

Fortunately I've reverted back to my Surge. It might also be incorrect but at least it seems more reasonable than the Ionic.

Thanks for bringing up this subject and explaining why Ionic's resting HR seems so accurate.

[SunsetRunner]

@NirMoshe just to clarify the technical side, you may check your HR using photoplethysmography just with your mobile phone. Turn on the flash, put finger on the back camera and turn on recording video. You will get something like this:

https://youtu.be/wlXcy0DbqNg

The red part is what the camera can see when I cover it with my finger ( you can see it's pulsing but it's barely visible ). The black&white is the very same thing but processed ( changed saturation, contrast and brightness so you can see it's pulsing clearly ).

You can easily count each beat and then say what's the HR. It's no different from what the watch does although, the watch uses particular light colour and probably better algorithms. I just did simple video processing. Nevertheless, it's still all about the light and any disturbance will affect the result ( you may see what will happen if you start moving the finger while recording, or let a little bit of light between phone camera and skin ). Not mentioning that it really matters where the watch is placed on the wrist, depends on skin, sweating etc. Photoplethysmography is very error prone and to deliver better results very often the readings are given with delay after collecting the data that at least look consistent.

On this video my HR approximately is 60bpm. If you play it back with 2x speed, it would be 120bpm. Now imagine that happening even faster. Here's where problems start when processing the input - detecting "flashes" when HR is lower and regular is piece of cake. Irregularities and speed make it more difficult. Even on the video, I've made you can see some irregular pulsations. Of course, devices like Fitbit went long way making the technology more reliable but I don't believe it 100% bulletproof. Even if we get rid of all technological obstacles there's still one which may be a cause of the error - human 😉

It is still a great tool to obtain certain data if you know what it means and how to use it. So it could be a reason to have a watch with HR monitor 😉

[NirMoshe]

what you say is reasonable but i want consistency in the HR , as i said i have two ionics one on the left hand and one on the right hand , on the left i started workout and on the right i didnt 

i wanted to see the same HR on both of them but its wasnt the case . i saw big different  between them 

this issue i cant understand. 

the compare here is between two ionics on same person same time with different HR somehow 

[SunsetRunner]

@NirMoshe two Ionics worn on different sides of your body will always show different results. I explained that briefly. It is not HR what is measured but the blood flow. The blood circulates through your whole body but it is a fluid and it takes time before it reaches particular parts of the body. the further it gets from the hearth the more it slows down as well. Imaging a wave coming to the beach. Where it originated it's where the impulse started. It takes time though to reach the shore and the speed may vary at the end. Both wrists will receive such "impulse" made of flowing blood and this is when a single heartbeat is recorded. For that reason, very often patient's pulse is measured on different fingers, palms and even on toes with use of pulse oximeter. Then some average is taken. Because readings may vary 🙂 Additionally, there are sometimes extra beats which may disturb the readings ( not sure if they are being filtered out by Fitbit software ) - ectopic beats ( you can see them even on the video I attached ). So yes - it's very likely two Ionics should show different BPMs if worn on two different hands. It shouldn't be a big difference though.

[bbarrera]

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@NirMoshewrote:

so my question is : is the HR calculating or measuring ?  

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Estimating, after a complex series of indirect observations and calculations.

Optical HRM is using light to monitor blood flow under your skin. It shines a light and looks at the light reflected back. Many things can interfere with the amount of light reflected back, and the contribution of light reflected back due to your pulse. Because of that, the data from the light sensor is filtered and processed, and then from the processed data the sensor module estimates heart rate.

The wrist is one of the most difficult places to reliably estimate HR from blood flow. When it works well, it relies on the fact that light will scatter in a predictable manner as blood flow changes, due to pulse rate and changes in blood volume.

On the other hand, when optical HRM fails to estimate HR, that is due to:

- "optical noise" 

- motion of your arms and body create more complex changes in blood flow, making it difficult to extract the pulse

- skin tone: different skin tones absorb light differently

- location: forehead is easiest place to extract HR from blood flow, the wrist is one of the worst places

- low perfusion: some people have low blood flow directly under the skin

A chest strap monitors the electrical impulses that cause your heart to beat, and for low-cost devices is highly reliable and the gold standard.