Fenix5 HR accuracy issue in cardio activity

Hi, i'm struggling with exactly same issues. Outdoor activities (running, motocross) are working very well but any indoor cardio activity never gets above 100 bpm. Somethimes it bounces between 70 and 90 bmp.

I have tried almost everything:
- different indoor profiles
- moving it on the wrist up and down
- different hand
- clearing the sensor
- tighten the strap
- even shaving my wrist just below :D
- lend it to different person

I don't have a chest strap but Apple watch on the other hand shows the right numbers.

Fenix 5 3.30 fw

This is all in my experience... I'm not saying this is correct but it's stuff that seems to be true for me...

The OHR is not very reactive. It is ok. You can do intervals with it but you need to warm it up sufficiently. You can't just hop on the machine and start doing intervals. You need to warm up for 15-20 minutes and even then the first interval might be kinda sucky. After that it usually settles in for me. Also obvious disclaimers like crank that sucker tight if you can... I also find it's often better to reboot the watch right before you start an activity and it starts responding much quicker. Otherwise it seems to me like it's still averaging for a while with your non-activity HR.

The chest strap is better. I got the plain jane chest strap and it works well but still needs to warm up. It's much more responsive. And it also can randomly decide to be off 30 bpm for me. With the chest strap I get much crisper peaks. I also had a HRM-Run monitor which was completely useless and I returned (I suspect it was a bum unit but I'm not sure). My regular "cheap" $60 chest strap is pretty good for me once it warms up and I sufficiently wet it down.

So it seems that if you do an indoor activity for "long enough" it starts tracking. I did some more experiments and in a moderately high heartrate (160 bpm avg) it started tracking after 5 minute or so (meaning it started to give similar results to the HR monitor of the cardio machine which agrees more or less with my chest strap)

But I tried also indoor rowing and after 15 min it was still showing a very low value. In all cases I made sure to wear it snug and in the correct position

So yeah, this seems to agree with the warm-up theory.

Not sure what to do for the indoor activities except to use chest strap always :/

What Garmin and a lot of other manufacturers are guilty of is not making it clear that OHR's are really only good for day to day fitness tracking and are not at all suitable for hard exercise or sports; where you really need a proper HR chest strap.

OHR's measure the colour changes in your skin that happen every time your head beats (your skin becomes slightly more red on each pump of the heart). Exercise also changes your skin colour, heat makes you get more red, compressing or stretching parts of your body makes your skin more or less red etc... all of which will affect the OHR readings.

For reading your general HR changes over the course of the day, or for recording HR during light activity (walking etc) then a OHR is great; but outside of that you really need to use a chest strap.

HRM-Run

This is all in my experience... I'm not saying this is correct but it's stuff that seems to be true for me...

The chest strap is better. I got the plain jane chest strap and it works well but still needs to warm up. It's much more responsive. And it also can randomly decide to be off 30 bpm for me. With the chest strap I get much crisper peaks. I also had a HRM-Run monitor which was completely useless and I returned (I suspect it was a bum unit but I'm not sure). My regular "cheap" $60 chest strap is pretty good for me once it warms up and I sufficiently wet it down.

I wouldn't bet on the HRM-Run being a bum unit, I have had 3 which exhibited the same result. I first had the "Red" or "New" one, and it would drop out at random times. I'd look at the watch, and the HR would be just a -- instead of a number. On Garmin Connect, it would show to have simply dropped out completely, or to a ridiculously low number, (ie on a treadmill, at 43 BPM when I was just at 115). I whined to Garmin, they sent me another one. Same thing. I decided to use the "generic" strap, with the cheap Chinese belt part, and had no problems. Then I sold that outfit, and purchased a Suunto Spartan Ultra, that came with that strap. I decided I liked the F5 better, so began using it again, but with the Suunto strap. Finally, a heart rate that shows what it should, really nice HR graphs. I bought a TickR-X, and it worked as it should, although the advertised running metrics only work on the Wahoo Fitness app. I thought "Okay, well, I don't like the idea of having to purchase the complete heart rate unit at >$100 every time the strap gets wonky." So I purchased an "old" model, with the module that pops off like the original Garmin/Polar straps. The belt on those is MUCH more comfortable, and not nearly as "stiff" as the "red" unit, but once again, it was back to the drop outs, and complete shut off's of the old "Red" straps. I've whined again to Garmin, and they are sending me another HRM-Run strap, the "new, red" one, which I suspect will be just as bad as the other 3. I think I'll invest in another Suunto strap just to be safe, as for me, it's the only one that is truly consistent, and works well. The Tick-R will be a backup. Oh, and I forgot to add, I always use the Electrolytic Gel on the strap before wearing them. At first I used spit, but then decided to use the gel, and it works flawlessly for me.
That's my story, and I'm sticking to it.. :-) Your mileage may vary.

What Garmin and a lot of other manufacturers are guilty of is not making it clear that OHR's are really only good for day to day fitness tracking and are not at all suitable for hard exercise or sports; where you really need a proper HR chest strap.

OHR's measure the colour changes in your skin that happen every time your head beats (your skin becomes slightly more red on each pump of the heart). Exercise also changes your skin colour, heat makes you get more red, compressing or stretching parts of your body makes your skin more or less red etc... all of which will affect the OHR readings.

For reading your general HR changes over the course of the day, or for recording HR during light activity (walking etc) then a OHR is great; but outside of that you really need to use a chest strap.

It's not so much hard efforts that are the issue, it's the variability and lack of responsiveness. I find the OHR tracks threshold efforts just fine, but less so with intevals.

One of the sources of error with OHR is that it can sometimes lock on to cadence, rather than heart rate. (Slight movement of the watch - especially if loose or poorly positioned, can let outside light enter the sensor in a rythmic way, which it misinterprets as HR). Ensuring you have good HR lock before you start the exercise, and warm up gradually, allowing the watch to track your HR as it increases, reduces the chances of cadence lock.

Temperature also plays a part. One of your body's responses to feeling cold is to direct blood flow away from the extremities and surface of the skin (to preserve body heat for the essential organs). This makes it harder for a wrist based OHR sensor to pick up your HR.

If you find a chest strap gives better results, then that is what you should use. The F5 is compatible with both ANT+ and BLE chest straps.

There's some OHR expectation management needed here. I don't think my findings are unusual in that I've consistently found OHR sensors (Scosche Rythm+ and Fenix 5 WHR in my case) to be:

OK for - everyday non activity HR, walking, steady state running, indoor cycling, and smooth road or trail cycling
A bit wonky for - Mountain biking, rowing, interval runs or run races
Chuffing useless for - strength training, circuit training and anything else that involves gripping or flexing wrist/arm muscles.

The Scosche Rythm+ does slightly better than the Fenix 5 WHR, when it's placed on my upper arm with the sensor on the outside edge of my biscep. So the bottom line is that even the (arguably) best OHR sensor on the market, optimally placed, cannot compete with a traditional HR chest strap for certain activity types.

What Garmin and a lot of other manufacturers are guilty of is not making it clear that OHR's are really only good for day to day fitness tracking and are not at all suitable for hard exercise or sports; where you really need a proper HR chest strap.

OHR's measure the colour changes in your skin that happen every time your head beats (your skin becomes slightly more red on each pump of the heart). Exercise also changes your skin colour, heat makes you get more red, compressing or stretching parts of your body makes your skin more or less red etc... all of which will affect the OHR readings.

For reading your general HR changes over the course of the day, or for recording HR during light activity (walking etc) then a OHR is great; but outside of that you really need to use a chest strap.

My Scosche Rythym + (Valencel sensor I believe) proves this untrue. It is dead on accurate (if only 1/2 second timing difference) with Polar or Garmin heart rate straps, which I've tested with walks, runs, step aerobic classes, and intense weight lifting sessions with rests between sets/exercises allowing extreme ups and downs in heart rates. Positioning of the Scosche is obviously different, but clearly all OHR sensors are not created equal. Perhaps you meant to specifically address WRIST based OHR.

My Scosche Rythym + (Valencel sensor I believe) proves this untrue. It is dead on accurate (if only 1/2 second timing difference) with Polar or Garmin heart rate straps, which I've tested with walks, runs, step aerobic classes, and intense weight lifting sessions with rests between sets/exercises allowing extreme ups and downs in heart rates. Positioning of the Scosche is obviously different, but clearly all OHR sensors are not created equal. Perhaps you meant to specifically address WRIST based OHR.

Yes if you want to be pedantic about it.

Since we are discussing the OHR on a wrist watch, on a wrist watch forum, I had assumed a context to the discussion had already been established.