Low heart rate reading during exercise

are you wearing it higher on your forearm ? what activity are you doing ? if your wrist is bending, then you need a chest strap

Left wrist over the same spot I wore my 235, right side of the strap ~1 cm from wrist. No noticeable twisting or bending of the strap of watch position seems very secure.

High intensity interval training. Lunge/squat type stuff with weights, mountain climbers, planks, and that kind of junk

today at gym while training (my ususall heart beat is between 78 and 116 depend of the intensity of each exercise), at an instant my smartwatch show me 50 bps!!! then it increases to 90...is it possible or some instant mulfanction of the watch?? (i was scared for a while with this number)

9415289 After much research I found that different styles of optical heart rate monitors vibe differently with different people. Ultimately I just got the chest strap. After a couple years I upgraded to a fenix 7 and while it tracks better it still isn't as accurate as the strap. Just takes a while to catch up, doesn't catch instant changes quickly.

Did this only happen after the upgrade, if so was it the upgrade to 13? 245 or 245 music?

The classic answer will be to back up activities and do a factory reset, though personally I'd try a power down restart before trying a factory reset

Speaking from personal experience, I had my 245 for less than a week when an automatic upgrade did much the same. Since it was a week old, I returned it, got a replacement, turned off automatic software upgrades and now read a lot of posts like this, like I was doing now, before deciding to let the watch do an update. I have done a major software update (on the replacement) with out any issues that I've noticed, but I've not done an update since 11.6.

There is some risk with updates, since Garmin will only let you roll back if the new installed version was beta and then only back to the previous version before the beta.

I'm happy with the optical HR on mine, I doubt it's really accurate for quick spikes but I've hit 150-170's on runs and I'm a senior runner. I don't care if for a few seconds I hit a higher number that doesn't get tracked.. I'm more concerned about what the average is for the effort expended as a fitness indicator. The HR updates well enough to monitor my HR during runs should I decide for an outing to run to an HR threshold (limit) for base miles.