Optical Heart Rate Fails During Intervals

I'm having the same issue. Did a long run on Sunday and the HR seemed pretty accurate (there were a few random spikes, but it quickly corrected). However, I ran intervals last night and my HR was not even close!

6 x 400m Using 935: https://www.strava.com/activities/958290893
4x 800m Using 920 with Scosche HRM: https://www.strava.com/activities/948363533

-Dan

are you guys getting HR locks prior to the run (and it not unlocking)? (the heart stops flashing)

It's interesting though disappointing to see I'm not the only one. I will recheck the heart rate lock issue next time though I wear the watch for abvout 30 minute before I start the run - thanks for the advice.

And anyone can search through the forum to find similar posts with all of the devices that have OHR. Take some time and have a look.

It's a shortcoming of optical heart rate technology. While it is getting better, you'll generally find that HR straps are recommended for activities of that nature.

standard things to do to improve OHR (From dcrainmaker and my memory)

Move watch up wrist away from wrist bone
Tighten strap
Try on inside of arm if on outside or vice versa
Try different wrist.

Sorry to hear that.
From other comments it seemed that the FR935 solved the issue with high intensity interval training that other Garmin watches had. It seemed to be a great improvement over the old Garmin Elevate optical heart rate sensor.

Till now, the only optical heart rate monitor that doesn't have problem with interval training is the Scosche Rhythm+ armband.

Can you continue informing us if you can resolve this issue waiting a couple of minutes after the heart rate icon stops blinking before the start of the activity and changing a bit the position on the wrist? I would also try a hard reset of the watch.

If you can't resolve this issue, this is a deal breaker for me, I won't upgrade to the FR935 and I will keep my Scosche instead.

Is it also quite individual so if one person is having problems with OHR then somebody else might not. However as mentioned interval training usually always presents the biggest challenge for the technology.

The Scosche isn't really a direct comparison as it is not wrist mounted and anyway you still would need some sort of device like a 935 to record HR from whatever source.

Yes, interval training is the biggest challenge for optical heart rate technology, because if there are big and quick variation in heart rate beats and in the cadence, it's easy for the optical heart rate to loose the track. And the point is that optical heart rate technology is quite individual, so for some people is all OK and for other is not, depending probably from physical factor of each person (probably color of skin, weight, percentage of fat, age etc.). DCRainmaker in his review showed that for him the FR935 worked good also for intervals. So I think that with the FR935 Garmin did an improvement in heart rate technology, because in other DCRainmaker reviews of older Garmin watches interval training was always a weak point also for Ray Maker.
In this forum I see that the big part of the people are happy with the optical heart rate of the FR935 for normal runs, but few people reported their experience with interval training, probably because it's a type of training that is done just once in a week and sometimes just near races. It would be a good thing if other users who owns the FR935 and have a good experience with normal steady run, report how it behaves in interval training (it's obvious that people that don't have good experience with steady run, probably will have bad experience also in interval training, and in this case I think that the problem for most people should be just a wrong wrist placement or a lack of heart race lock at the beginning of a run).
If other users report about their experience, we could see which is the general trend, for example it could turn out that the FR935 functions good in interval training for circa 50% of the users.
I would also say that in any case the most important thing is that the optical heart rate monitor is correct in steady run and that the algorithm is stable also in uphill and downhill and doesn't confuse the heart rate beats with the cadence. The interval training workout is done not frequently (usually just once in a week), so in this occasion one could just sync a heart rate strap. After all, I think that it would be not a big problem if it turns out that the FR935 is not so good in interval training for the most percentage of users. But it is interesting to follow how Garmin improves with time his optical heart rate technology.

Sorry to hear that.
From other comments it seemed that the FR935 solved the issue with high intensity interval training that other Garmin watches had. It seemed to be a great improvement over the old Garmin Elevate optical heart rate sensor.

Till now, the only optical heart rate monitor that doesn't have problem with interval training is the Scosche Rhythm+ armband.

Can you continue informing us if you can resolve this issue waiting a couple of minutes after the heart rate icon stops blinking before the start of the activity and changing a bit the position on the wrist? I would also try a hard reset of the watch.

If you can't resolve this issue, this is a deal breaker for me, I won't upgrade to the FR935 and I will keep my Scosche instead.

Waiting for the heart icon to stop blinking (it getting a confirmed lock) has almost completely solved oHR issues for me. High intensity interval training becomes like 90-100% accurate instead of like 30-50% (completely approximate numbers, but you get the idea). There will still definitely be times it gets "lost", but if you let it get a full lock, it's pretty darn good.

Still, if I want hyper accurate HR numbers for a run or am doing a race or a group run that I can't "wait for it to lock", I'll just wear another HR strap (Scosche or HRM+RUN).

I don't need medical precision, and I don't mind if the FR935 will lose the correct heart rate once or twice in a run, so it seems that I have to continue to pile up money to buy the FR935 :)