Wrist HRM problem - goes up way too fast at beginning of run

OHR works by measuring the change in light reflected back from the LEDs with the surge of blood with each heartbeat. One of the problems with wrist OHR is that with the movement of the arms, external light can enter the sensor in a rythmic way, and fool the sensor into locking onto your cadence, rather than your heart rate. Wearing it away from the wrist bone (as you are doing) so that there is a good seal against external light is one way to avoid this, the other is the ensure the band is snug to avoid any "bounce" of the watch on your wrist - I find I have to have the band one notch tighter while running than I do for 24/7 monitoring.

The other big problem with OHR is that it is slow respond to changes in your HR. I suspect that part of the problem is that the watch has trouble following the increase in your heart rate as you start your run, and locks onto your cadence instead, before picking up your real heart rate again. Letting the watch get a good initial lock on your heart rate ( wait for the heart icon to go solid before pressing Start), and a gradual warm up can help here.

The slow response is widely acknowledged to cause problems with HR-based interval training using OHR across many brands (not just Garmin). In your case, it seems to track well with longer intervals of 6 min hard, 1 min recovery, but shorter intervals (eg. 20 seconds) can cause problems.

I would suggest trying these alternatives before getting a chest strap or returning the watch.

This is normal behavior. Usually caused by the watch locking into your cadence, before providing correct measurements.
You might get around this by letting a minute pass after gps lock, before you start your run.

I see exact same behavior. Also happens when cycling (so definitely not a movement issue). I've tried all the different ways to wear the watch with only some success by having it way up my forearm. It still wouldn't work every time and I don't like where it there (constant feeling it is slipping down my arm) so I finally gave up and wear the HRM-RUN strap.

Would be nice if Garmin Connect gave us an easy way to delete the HRM track when it is out of whack so it doesn't mess up trends, etc. Since no way to delete it, I don't take the chance on having the bad readings anymore.

In my case it takes about 4-5 min before snapping to an accurate HR. I suspect this is when pulse gets strong and fast enough for it to sync. I don't see that the high readings match my cadence while running or biking though. It's usually somewhere in between actual and cadence so I'm not sure I buy that explanation.

OHR works by measuring the change in light reflected back from the LEDs with the surge of blood with each heartbeat. One of the problems with wrist OHR is that with the movement of the arms, external light can enter the sensor in a rythmic way, and fool the sensor into locking onto your cadence, rather than your heart rate. Wearing it away from the wrist bone (as you are doing) so that there is a good seal against external light is one way to avoid this, the other is the ensure the band is snug to avoid any "bounce" of the watch on your wrist - I find I have to have the band one notch tighter while running than I do for 24/7 monitoring.

The other big problem with OHR is that it is slow respond to changes in your HR. I suspect that part of the problem is that the watch has trouble following the increase in your heart rate as you start your run, and locks onto your cadence instead, before picking up your real heart rate again. Letting the watch get a good initial lock on your heart rate ( wait for the heart icon to go solid before pressing Start), and a gradual warm up can help here.

The slow response is widely acknowledged to cause problems with HR-based interval training using OHR across many brands (not just Garmin). In your case, it seems to track well with longer intervals of 6 min hard, 1 min recovery, but shorter intervals (eg. 20 seconds) can cause problems.

I would suggest trying these alternatives before getting a chest strap or returning the watch.

thanks for your suggestions, of which some have been given by Garmin too: I wear the strap 1 notch tighter, or push the watch up my arm until it is quite tight around my arm. I wait for the heart symbol to go solid. But the cadence thing strikes me, my cadence at the beginning of a run is around 140... I will experiment with that, see if if I start at a 'running' cadence of 110 steps per minute the watch will lock to that or the problem doesn't occur.

What I don't understand is that my watch seems to be able to read my pulse for 24 hours a day fairly correctly, except for these 2 first minutes of my run. Just feels odd.

Others, thanks for your suggestions and feedback!

Personally I don’t think this has anything to do with the OHR nor cadence... I made a similar post earlier today. For me and my wife this just started happening over the past few weeks. She has the fenix 3 while I have the fenix 5x. Both of use external HR monitors exclusively... for me, it had me at 160 10 seconds into my run this morning. After about 10 minutes it stabilized to what I normal see — 135-145... my wife, not cleared for running again yet, did a 3 mile walk while her HR strap had her at 210! Something is wrong with the HR monitoring algorithm.....

I've been experiencing this jump to clearly wrong HR during first 3-5 min of an activity for a year now on F5. I see it on both runs and bike rides. The rate is generally not in the range of my cadence so not sure I buy that unless it is somehow calculating a HR value halfway between actual and cadence which is closer to what I usually see.

I decided to use my Edge 520 on my bike while on a trainer to have better view of status during workouts vs F5. Over past year I've never had a cycling workout (indoor or outdoor) where the HRM was not out of whack at the start. But on past few workouts where I've selected to broadcast my HR from the Fenix to the 520, it is giving normal readings right from the start... This tells me it is not watch placement or not detecting HR until my heart starts pumping harder but an issue with the watch firmware.

Not sure how I'll confirm this during running since I don't know what I would broadcast HR to...

OP's HR graphs look normal to me. Looks like you are running in chilly weather and you are not yet warmed up at the beginning of the run. It is fairly typical to see a high HR at the beginning of an activity until you are warmed up. I see the same thing in the winter but not in the summer. I also use a separate HRM with the same result. I don't pay too much attention to HR spike in the first 7 minutes or so when starting a run. These days I try to warmup a bit inside with some active stretching and lunges before going out for a run. It helps some, but does not eliminate the spike.
https://runninginsystems.com/2015/11/07/question-from-a-reader-why-does-my-heart-rate-spike-at-the-start-of-a-run/

A couple of things to consider. If you watch is showing a lock on you HR before you start running it should be reasonably accurate when you start you run as long is it is snug on your wrist. That being said, I have had problems with the Fenix 5 built in HRM during a workout where it has locked onto cadence. I think what has happened in this case is that exposing my wrist to cold temperatures changed conditions of the skin around my wrist. When this happens my wrist is cold and the skin is flush and red.

For the recent post from Osea. Are you saying it is not normal when you are using just the watch and normal when you use the watch to broadcast to another device? If so, try it a couple of times to see if the trend continues. I suspect it may be coincidence. Note that cadence during running can affect the OHRM where road surface and not cadence can affect the OHRM while riding.

While I have had a few problems with the Fenix 5 HRM, it hasn't been on every run. Just an occasional problem in the middle of a run. Hopefully it will be more reliable when the weather warms up for me.

Hi Carl. Yes, not normal whenever using just watch HRM but normal the last 4 times I broadcast the HRM from the watch to the Edge 520. I'll be trying again on next workout.

I pretty much gave up on the F5 HRM during workouts for the past 4-5 months due to this behavior. I've never seen the high readings at at the start of an activity using the strap. Unfortunately, I lost the strap a few weeks ago which is what caused me to start using the watch HRM again. I bought a replacement strap yesterday but will continue to use test the broadcast method while cycling. For runs, I'm back to the strap until I hear that something has changed with the F5 firmware related to this.

Other optical sensors suffer from the same issue, especially in cold - even the golden standard that Scosche Rhythm+ used to be suffers from this.

Current generation of OHR sensors is not yet at the level that could seriously compete with chest strap accuracy - although chest straps suffer from their own issues (which, due to how long they are on the market, people kind of learned to live with). The strenght and value of OHR is in 24x7 monitoring and "casual" activities where you just need to have a ballpark HR number.

I kind of feel sorry you replaced a functioning watch twice for this...

Report after another workout tonight: Started the stationary bike using Edge and broadcast HR from Fenix. HR as I would expect... first 5 min 70-80 bpm range. Stopped and switched to recording workout solely on Fenix. Immediately jumped to 115-125 bpm and then after about 7 min suddenly dropped down to 80-90 and slowly increased from there as workout continued. This tells me it is not the sensor itself that is the issue. It has to be something with the simultaneos combination of the sensor and recording of the activity on the watch.