Fenix 7 pro reported way too low HR compares to HRM dual during indooe cycling

alanyu said:

I didn't start the activity on Fenix

alanyu said:

Is my unit faulty or I did something wrong?

Yes, you must start the corresponding activity profile.

So what's the difference in the algorithm of tracking HR in daily/smartwatch mode and activity mode? I previously supposed both should give me the accurate/identical HR.

alanyu said:

I didn't start the activity on Fenix, just let it track my HR as in daily life.

This!

The OHR sensor has a low power mode for 24/7 tracking, and a high power mode for activities. (If you peek under the watch as you start an activity, you can see it change from strobing to solid On). The low power mode does pretty well for 24/7, but it does struggle when your HR get above 120 bpm.

Normally this is a non-issue, as Auto-Detect will pick up the wrist movements from walking, running, or outdoor cycling, etc and trigger the high power mode. But indoor cycling is one of those unusual cases where because your wrists are almost motionless, Autodetect doesn't trigger the high power mode.

Record an activity while indoor cycling - should resolve the issue. You can discard afterwards if you want.

I tried a short indoor easy spin today, and started the Indoor cycle mode on my Fenix. However, you can see that the Fenix tracked my HR correctly in the first half (25 min), but in the second half it constantly tracked low HR. I noticed the low HR on Fenix during the ride when I took the water, and only after the movement of my wrist/hand, the Fenix reported correct HR for some minutes. In the second figure, you can see the sawtooth line during the second half, corresponding to my wrist movement (I raised my wrist to check several times after the first observation).

I think either the HRM logic of the Fenix 7 pro in the current firmware (the latest public version) is buggy/broken, or my unit is faulty...

emmm... interesting. Never read that page before... I will try to loose the fit next time ... (Activities that flex the wrist may create an effect similar to wearing the watch too tightly and restrict blood flow. Examples include, but are not limited to:) 

Or try to wear the watch slightly farther up the wrist.

OK a loose fit did make HR of Fenix more accurate during indoor cycling, not as good as strape though, but I feel it too loose in daily life... It's not possible to keep the watch a bit up as it would drop down during the activity.