HRM unreliable with sport activities

[lunctis-viribus]

For a time I was wondering why my heart rate was always around 100 on the Bangle.js 2 during intensive sport activities. This month I double measured my heart rate with a Polar H10 device during intensive running. This were the results:
Measured with Bangle.js v2 (average heart rate of 96):

Measured with Polar H10 (average heart rate of (170+):

So clearly there is something wrong with the HRM of the Bangle.js v2. I am using the Recorder and the Run+ app.

[gfwilliams]

There are a few discussions around this on the forum, but you are comparing an ECG-based heart rate monitor stapped 6 inches from your heart to the Bangle's light-based system which is strapped to your arm and waved backwards and forwards at high speed while you're doing exercise.

It's not that there's something wrong with the HRM (you could however check you removed the protective tape from it - that doesn't help), it's just that there are serious limits to what can be measured with a PPG system like the Bangle's during heavy exercise. If you look at the raw data that comes out of it when exercising it's effectively random noise - it's very hard to dig useful information out of it - but that'll be the same with pretty much any device using light to measure HRM on your wrist.

You're welcome to experiment with different algorithms to try and make sense of the raw data (I did have a push a while back to try and get data to work with but there was very little interest). I've been through several iterations and have ended up settling on the manufacturer-provided algorithm, which seems to be a decent compromise for most situations.

There is however an app which allows your Bangle to connect your Polar H10 and then record the Polar's HRM data instead of the inbuilt one, so that could be an option if you want super accurate heart rate without needing your phone.

[fanoush]

This is interesting. While it is really tricky and mostly it indeed doesn't work very well once the PPG sensor is moving rapidly, I am still surprised the manufacturer provided algorithm gives such bad result for you. I have one SMA Q3 watch still with original firmware and I did use it while running many times and it was mostly reliable in the sense that it went to 160-180 rates and I could somehow use that to slow down or speed up to keep the HR in some interval. And it should be hopefully the same algorithm binary used there. This is much older revision of the watch with no barometer hole and older VC31 HR sensor. It would be interesting to test the current SMA provided watch firmware for current Bangle 2 watch model if the issue is there too. Which reminds me that I wanted to test how to restore SMA firmware and get back to Espruino just via DFU over bluetooth. If it works then more people could test it if interested.

And BTW @lunctis-viribus it may help to keep it more tight so the watch vs your skin moves less. While even the rapid movement of watch tightly strapped to the hand is not ideal for PPG, it is much worse if the watch is loose and moves on your hand, then it is really just a random noise.

[nravanelli]

@lunctis-viribus We actually just published data examining the validity of PPG signal with the Vcare algorithm vs the Polar H10 (and also the step counting algorithm within the Espruino firmware). These data reiterate the answer by @gfwilliams.

If you want high accuracy HR at higher intensities, especially when you have high arm movements - best to pair a HR strap. This is true for other wrist based PPG sensors; although their motion artifact detection is getting progressively better as technology matures.

[lunctis-viribus]

Great paper! It indeed confirms that when moving, the Bangle.js2 has a significantly lower bpm than the Polar H10, especially when bpm is 100+. This explains the low CCC of 0.54 for Steps > 0. Thanks for mentioning and publishing this paper @nravanelli !

@fanoush next time I will tighten the watch strap, thanks for the suggestion.

[thyttan]

next time I will tighten the watch strap

Beware of this though: https://github.com/orgs/espruino/discussions/7319

I woudn't worry if you use a silicone strap since it's so flexible. I use a nylon fabric strap that doesn't flex and if tightening it too much the lugs are at higher risk of breaking.

[lunctis-viribus]

next time I will tighten the watch strap

Beware of this though: https://github.com/orgs/espruino/discussions/7319

I woudn't worry if you use a silicone strap since it's so flexible. I use a nylon fabric strap that doesn't flex and if tightening it too much the lugs are at higher risk of breaking.

Thanks. Actually, this is my second Bangle.js2 because a broken strap connection is exactly what happened with my previous one. And I am using a silicone strap band currently.