VERY Inaccurate OHR Cold weather

Does it fit to your wrist like your Fenix does?

I don't have a 945. But my 735 behaved the same way while running in winter. Although my arm and hand were covered by warm clothes and gloves the reading was too low after some time. I thought that I haven't worn it tight enough because my wrist is a bit thinner if it's cold. But one hole less it's not very comfortable when I move my wrist. In bed when everything is warm and I sometimes sleep on my arm that hole would be very uncomfortable. So I leave it a bit loose. Makes marks enough on the skin... I even tried to keep the watch completely under the sleeve and the gloves. But that didn't help very much. Not only that I couldn't read it this way. So I decided to buy the HRM Run. I don't know if this could be a solution for you. Obviously oHR hasn't improved that the 945 has the same problems or it can't be improved because oHR has some disadvantages.

I'm having the exact same problem. Basically any winter activity shows inaccurate heart rate on my FR945. Garmin, any thoughts/fixes for this? Honestly, my old fitbit worked better in a number of ways. It's frustrating given the price paid for the 945!

I also experience significantly lower readings than should be while ski touring(backcountry skiing).

I do understand this but I don't understand why it seems to work fine on other devices, i.e. my old fitbit or the Fenix mentioned above. 

Thanks for the response and info, though!

It could be the weight difference between devices as one may have more "play" on the wrist.  Some sensors sit differently on your wrist due to design.  Some sample at different rates.  And some devices just work better than others in different circumstances.  The oHRM is more of an individual thing than a this brand/model works best.  You probably don't want to hear it (understandably), but the best way to avoid this is a chest strap.

Hi!

This issue has been discussed here in the past.

The problem is not because of the cold. The issue occurred after a firmware update during summer 2019. Before it worked ok during roller ski training (classic skiing as activity on FR945).

After the update the maximum HR was around 115 bpm if I remember correctly.

Every Optical Heart Rate Monitors of all kinds, from all brands, are going to be poor in cold weather because:

~Optical Heart Rate Monitors are not reading actual Heat beats (Primary) or your pulse (Secondary), but guessing your heartrate via shining an LED light on your skin and reading blood flow under the surface (Tertiary at best). 

Now, what happens when the weather is cold? Blood flow throughout the body is restricted, in particular to your extremities (i.e., hands, arms, feet legs, etc..). Because of this, the OHRM is doing it's best, but there just isn't anything to track. Most brands try to tailor their algorithms to compensate, but it's still grasping at straws. 

Here's an example. I live in Minnesota. Yesterday it was -11F (-24C), and I had made a quick run to my mailbox (approx fourth of a mile [402m]). I was indoors where it was warm, and HR was a bit elevated (I was moving around a lot at the time) at around 87bpm. It was cold, so I decided to sprint down the block, get my mail, and run back. I had a thermal jack on. Do you want to know what the BPM was? 43, the whole run. As soon as I got back into my home, it began to rise again. Within a minute, it was sitting around 106bpm (I really sprinted, it was that cold).  For the record, my Resting heart rate is 43. 

You can try mitigating the blood flow issues by warming up your body before going outdoors, wear the watch insulted with clothing, but there's always going to be an issue with cold weather and OHRM. I would suggest buying a chest strap if you want the accuracy.