The runs (simple runs NO trail runs) were 2 km each and the bike rides were 5 and 10 km with Polar H10 on. It gives me an error when I try to upload the screenshots from Connect.
They were intense (165-179 bpm). Just wanted to do those two runs required for the Vo2 max and I made them one after the other with 5 minutes break between them.
It does not matter whether you use an external HRM or the optical wrist HRM. Just give it more time (days, not 5 minutes) and run for a longer time/longer distances.
I have Quatix 5 + Polar H10. All work fine. You need to wait 2 weeks and do GPS running twice a week at least 2km and more. I had the same situation every watch exchaged to a new one.
Originally in Garmin paperwork it mentioned needing to run moderate to high intensity for 10 minutes, iirc, at or at least the 10minutes part. Unless pretty slow a 2k run will likely have your heart rate still climbing / warming up. so better to run a warmup 5-10minutes... then increase to a medium high effort for 10-12minutes... then cooldown. I find 'tempo' runs often will update my vo2max for the better while long slow runs or longer runs with fast towards end will often lower it
