Optical HR grossly underestimates HR on slow uphill running / walking

I trained a lot with a chest HR for years and I know what 100bpm, 140bpm or 170bpm feel like. When doing trail runs in mountains I have very steep uphills. I have to walk with poles. I'm talking 15% grades over technical terrain. My flat running pace would be 5:00/km, in this kind of very steep uphill it can drop to 12:00/km. My heart usually reaches 160-170bpm, i can hear my heart pumping, I sweat, I can't talk. Now since i have my garmin 5x with optical HR, my reading on my HR drops dramaticly to like 100bpm on these ups. It's impossible. At first I though it was the jerking of running, but I found out it is fairly accurate when running downhill and flats when much more jerking occurs. Its also accurate cycling.

It must be some kind of algorithm to eliminate outliers, like mistakes of the optical HR. This "clipping" algorithm kicks in when the pace drops to walking speed (or even slower) because it must assume "it's impossible someone running doing 12:00/km to have a heart rate of 170bpm). I think this is poorly though for a device done for trail running and climbing, not just road running.
I have two examples if you want to see.
This with a chest strap, notice the bumps on the HR when I climb:
https://www.strava.com/activities/380044957
And this is with the optical HR garmin 5x. Notice the drop on HR on every uphill and how it correlates to plunges in pace.
https://www.strava.com/activities/1118717277

There should be an option to turn off this kind of control or whatever this feature is, specially for sports like trail running.

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0 mcalista over 6 years ago

OHR works by detecting light changes with the surge of blood with each heartbeat. But stray light getting in under the watch can cause mismeasurement, and when this occurs in a rythmic manner, can cause the OHR to lock onto your cadence rather than your heart rate. I haven't tried OHR with my hiking poles, but I would imagine that the wrist flexing associated with poles might be the problem. AFAIK, there is no clipping algorithm based on pace. Normally cadence lock leads to over-reporting of HR while running picking up a typical cadence of around 170-180, but I imagine your cadence while hill climbing with poles is probably around 100?

The most common cause of OHR problems is poor positioning and placement. The watch band should be snug, and positioned on the fleshy part of the wrist, well away from the wrist bone. I'd recommend positioning the watch even higher on your arm to avoid interference from your poles - especially if you are using poles with a wrist stap.

If this still doesn't work, the good news is that the F5X still works with chest straps (and now works with BLE as well as ANT+). If chest straps have been working for you in the past, then you can keep using them.

0 lourencobray over 6 years ago

OHR works by detecting light changes with the surge of blood with each heartbeat. But stray light getting in under the watch can cause mismeasurement, and when this occurs in a rythmic manner, can cause the OHR to lock onto your cadence rather than your heart rate. I haven't tried OHR with my hiking poles, but I would imagine that the wrist flexing associated with poles might be the problem. AFAIK, there is no clipping algorithm based on pace. Normally cadence lock leads to over-reporting of HR while running picking up a typical cadence of around 170-180, but I imagine your cadence while hill climbing with poles is probably around 100?

The most common cause of OHR problems is poor positioning and placement. The watch band should be snug, and positioned on the fleshy part of the wrist, well away from the wrist bone. I'd recommend positioning the watch even higher on your arm to avoid interference from your poles - especially if you are using poles with a wrist stap.

If this still doesn't work, the good news is that the F5X still works with chest straps (and now works with BLE as well as ANT+). If chest straps have been working for you in the past, then you can keep using them.

Thanks for the answer. Yes, I'm using poles indeed, I will test without them and getting the watch higher. However I feel the watch is tight and snug, even more than running fast downhills or flats. I doubt this has to do with OHR being unable to read, but I'll give it a go. Cadence presents the same problem as pace in these very technical ups. As for the chest strap, I stoped using it. In very long train runs (4h+) i would almost always start to become a nuisance, cutting or bruising the skin. I have problems already without needing yet another peace of gear to handle :D I actually hing OHR of the 5x is very good, better than I expected. It's jut these ups and suspecting something of a software problem.

0 zviolett over 4 years ago in reply to mcalista

I'd disagree. I have found that no matter the positioning, it does not work well on steep uphills with poles. Watch will work perfect, then hit a hill with poles and the HR goes down to 100 (despite me going harder). Then once flattens out, HR goes back to normal.

Yes, Chest strap is by far the best answer but is a work around as I'd prefer as below not to need a second piece of gear.

0 jupjap over 4 years ago in reply to lourencobray

i also have to use the chest strap for all activities with poles. If the problem actually is the shake of the device during impact and when pulled off ground, or what i suspect: the muscles lifting the OHR-Sensor from the skin (very thin wrists, no fat).... i dont know .

for me it is a given fact that no matter how bloody tight i fix my watch or how high. with poles OHR won't work on my arm.

0 Rob over 4 years ago in reply to lourencobray

Relatedly, given trekking poles are part of this discussion, are your steps also undercounted when using poles? Mine are when using poles with my Fenix 5 by approximately 40 to 60 percent. I noticed this on a recent backpacking trip, where my watch registered about half the steps as my phone in my pack hipbelt pocket. Kind of a bummer from a data perspective.

0 jupjap over 4 years ago in reply to Rob

yes, step counting is not working correct with poles, same for me here.

i just always use the chest strap so i got that going for me (even if this does only solve the OHR problem but not the step counting issue).

0 6981059 over 4 years ago in reply to jupjap

It's not just poles. I was showing an astonishingly low HR of 100bpm while powerhiking without poles up 2,500' of vert. This is on a Forerunner 245.

0 dezurtrat over 4 years ago

Has anybody had a solution to this? This thread is over three years old. Just curious. I have a Fenix 5s which the Wrist Heart Rate Monitor appeared to be pretty accurate for about a year or so. It suddenly began reading all over the place while running. If I switch to the chest strap then all is well again.

I will note that over the last year I have lost over 30 pounds and my body fat has dropped form 18% to 12%. Is there any link between body fat and the accuracy of the WRM readings?

It looks to me like a lot of people are having issues with the WRM on the Fenix 5s. It's very frustrating.

Thanks!

0 Daniel_Ilg over 4 years ago in reply to dezurtrat

When you are serious about training w/ HR then use a chest strap.

0 dezurtrat over 4 years ago in reply to Daniel_Ilg

Well, I understand your point but I specifically purchased this watch because of the wrist HR monitor. It’s not simply a little inaccurate, it’s so far off an accurate reading at times to be any use at all.

Its a feature the watch was sold with and I expect it to work.