Optical HR grossly underestimates HR on slow uphill running / walking

OHR on the wrist seems to work for some people all of the time, but it has never worked reliably for me whilst running. Sitting still, cycling etc it all works fine but when I'm running it quickly locks onto cadence rather than measuring heart rate, for the same reasons other people have mentioned.

Whether you expect it to work or not has little effect on the heart rate monitors accuracy... The technology is not perfect, if you want accuracy all of the time, use a HRM strap. No  wrist optical HRMs are as accurate as a strap.

First of all; I gave up on whrm a long time ago. It doesn’t work!

A little more nuanced; resting heart rate seems ok. Cycling seems ok. Running is likely to picjk up my cadence.

A few tips which might help. You say you lost wight (good job!!!). Maybe you don’t wear your watch as snug around your wrist as you used to do. Or maybe you wear it a bit more towards your wrist. Try wearing it as snug as possible and as far away from your wrist as possible.

Maybe temperature has something to do with it. Is it colder than normal or is your body reacting different to cold? Do you have colder hands since you lost weight? There might be less blood flowing to your hands.

But in the end you have to accept that whrm doesn’t work.

I also have this issue, mainly when using hiking poles. Even when on the flat, hiking poles makes a lot of the data coming out of my Fenix 6 inaccurate. It seems to do ok with running. I'm still working on testing it. My solution is going to be to turn off HRM when using poles until I know this is fixed. Garmin should make a note of this when starting activities like "backcountry skiing". It majorly skews a lot of training algorithms to have the bad data from HR. Garmin, do you just need more data from people with hiking poles to train your tracking algorithm? I'd be happy to provide.  

Joel_James said:

I also have this issue, mainly when using hiking poles. Even when on the flat, hiking poles makes a lot of the data coming out of my Fenix 6 inaccurate. It seems to do ok with running.

Unfortunately Joel, this isn't a fault with the hardware.  It's a software issue that Garmin chooses to use.  Why Garmin calculates HR differently based on activity is a question I've yet to find an answer.  The HR sampling rate should be the same regardless of activity as far as I'm concerned.  From Garmin's support website:

Additionally, HR is calculated differently for each activity.  Use the activity app that matches the activity being done.  For example, using the Elliptical app while running outdoors could result in incorrect HR being recorded.

https://support.garmin.com/en-US/?faq=xQwjQjzUew4BF1GYcusE59&productID=621922&searchQuery=optical%20heart%20rate&tab=topics

I had the same issue yesterday with my Forerunner 245, without using poles. The hr reading was 80-100, despite feeling I was in the 140-150 range. Our pace was very slow climbing up, but also very wet due to the heat and humidity. I was completely drenched. I tried drying my wrist and watch several times, but it didn’t help. Eventually, I stopped and let the watch dry, off my arm, for a few minutes and give my arm a solid drying too. Then it worked. It was a bit cooler and less humid at this point too. However, our pace may have picked up at this point as well, so I am not 100% convinced that it was the moisture that caused the faulty reading. 

no poles - 1500 foot ascent over .9 miles at end of 6000 feet of climbing. I was pushing it. Breathing pretty hard. Tried reading my own heart rate - estimated it around 150+. Garmin reported my highest heart rate at around 110 -- no way. 

Thought it was wetness -- maybe. I was sweating, and had sunscreen on, but tried drying wrist, switching to other arm, nothing changed it. Other climbs that day had been more accurate - though pace was higher because they were less steep. Who knows. Pretty stupid though, I would like to know where I was at, or at least something approximating accuracy. 

Yeah, I just had this exact same issue.

I started my run with 30 minutes of running in mild incline/decline asphalt with an averate HR of about 170, then I started the steep rock stairs up to a 450 meter high mountain top, and within a minute my HR had plummeted to 130-140 on the watch. As I was nearing the top 20 minutes later, and obviously close to reaching my absolute maximum HR, feeling the sharp taste of blood in my mouth, my HR was apparently at a relaxed 125. When I stopped at the top, it quickly went up to 170 (this was while I had been standing completely still for a minute!). Going down the same stairs it was showing around 160.

I probably have to buy a belt, but my question is: will a Garmin HR belt definitely be correct, or do I risk the belt using the exact same formula or whatever it is to miscalculate in the exact same way? 

In general, detecting HR with a sensor strapped across ones chest is intrinsically easier than the wrist based sensors. The chest strap moves a lot less with respect to your body and has a larger area, and larger signal it can detect. Your watch on the other hand moves a lot with respect to your wrist during activity, so there is a lot of filtering required to reject that movement read by the sensor vs the actuation of your body during a heart beat.  In my experience with a couple different chest straps, even an old one, all of them track much better between my exertion and heart rate it reports (though not always perfect). I think all wrist based heart detection methods from other manufactures likely would struggle with this compared to a chest strap, but that said, given this is a premium top notch product, I think more could be done by Garmin to make it better by training more types of movement to reject (perhaps they are already trying/working on this). Or at least they could report when it thinks its not confident in the reading. 

Thanks for the response. Alright, I'll give a chest strap a try. I assumed the HR monitor was simply reading the HR, didn't realise how much filtering was required. If it was simply reading HR, I would've thought that it theoretically should be much easier in the steep uphill, as my SPM is less than half of what it is when running on relatively level ground, and my arms are a lot more static. Had my most intense workout in a long time yesterday, so a bit sad that I couldn't analyze the numbers. 

I have a chest strap and I am going to try it out once I get on some steep mountain climbs. I've been rehabing an injury so sadly haven't had the chance to do it.