Strange behaviour with Garmin HRM

Francesco Pagano

Hello,
my Garmin HRM-Pro chest strap is starting to behave weird and I wanted to check whether anyone has experienced something similar.
I always use the chest strap for running, treadmill, etc. with my S9PP. The strap has been great so far, but it’s almost 3 years old and it starts being unreliable when I take HRV readings with my phone in the morning.
When running, I noticed - in particular during the initial warm up - that the HR readings go up and, especially down; say I’m in Z2 at around 140bpm, the HR suddenly drops to something around 80bpm, more rarely jumps above 170bpm.

The strange thing I noticed is that if I pause the activity, on the pause screen the watch shows what I assume is the right HR. I tried 2-3 times in a short sequence this morning, and it did it every time: “wrong” reading while exercising, right one while paused. Could this depend on the watch somehow?

Swaddy61

@Francesco-Pagano My experience with Polar and Suunto belts is that the battery needs changing every year, and the strap itself (not the plug in unit - not sure if the Garmin unit plugs into the belt) lasts 3 ish years, and then needs replacing.

So, if you haven’t changed the battery that is job one, and after that, a new strap, without the plug in unit. From memory, the Suunto and Polar straps were €30 ish, compared to a complete new belt (with plug in unit) of about €80 ish.

Swaddy61

I should add that I don’t rule out a watch problem, just that I think the other suggestions are more likely!

Francesco Pagano

Thanks for your answer! I normally change the battery before 1 year, last time I did it in October and I don’t think it’s empty by now.
Unfortunately this model has a unit that doesn’t separate from the belt, but I need to investigate on what options Garmin offers to replace the belt, it is definitely worn out.

I am still curious though why the watch reads a presumably correct value while the activity is paused

Swaddy61

@Francesco-Pagano That is a little strange. It is possible the watch defaults to Optical HR when you pause, then tries to read from the belt again when you restart?

I can’t think how else that would happen!

false

Hello! I can relate.

I was training with an hrm-dual for a year when I started to experience almost the same issues.

On the ‘pre-training screen,’ there was always a correct HR, but right from the start of any run, it got stuck on 80. Then, in 8 - 10 minutes, it started to show correct measurements (usually), but sometimes it peaked at something like 160 - 170 bpm and got stuck again until the very end of training.

So it took me one or two training sessions to realize that something was wrong with the belt because previously I noticed that a rubber part of one of the electrodes had peeled off a little.

Luckily, I had a brand new Polar soft strap and a Polar H10 transmitter, which one I used for around 10 months but more than a year ago, and since then, it was waiting for its time on the shelf.

And you know what? The experience was nearly the same… 80 bpm at the beginning and 170 after a few minutes. Nothing changed with a new battery as well. I attached Garmin’s transmitter - nothing new. I also changed the battery in the HRM Dual - no results. I even did a reset of h10 and nothing has changed.

I have also tested these combinations during a casual walk - and it was fine. It was very interesting.

Also, I noticed that sometimes the watch wasn’t abled to connect to or to find a transmitter before my training.

So I thought the problem was either in my watch or in the belt.

Knowing what kind of buggy firmware Suunto released in December, I decided to test these sensors with the Garmin FR245 watch. The result was also bad, but slightly different. The heart rate readings were correct, but judging by the graph in the Garmin app, the heart rate monitor turned off approximately every 10 minutes for 10-20 seconds - there are gaps visible on the graph. So, the problem was not the watch.

A couple of days ago, I bought a brand new HRM Dual and did two running sessions with it on me. Finally, I got correct HR measurements… I want to try this new Garmin transmitter but with my almost new Polar soft strap one day just to clarify whether the strap is okay or not.

Since the new Garmin set resolved the issues, from my point of view, the problem might have been in these two pins by which the HR transmitters are connected to the belts. I always detach the transmitter after training and attach it prior. Per year, it’s like 400-500 of such cycles. Maybe they wore out a bit, and the contact between the parts was broken? With the new transmitter, I have to use a little force to attach it to the belt. The old ones fit much easier.

I also rinse both the belt and the transmitter with water after every use. But for me, it seems it doesn’t prolong the life of HRMs for long.

Mff73

@false
Nice tests

marcrie

@false I’ve had a similar issue with a polar h9 strap. I connect it to the polar app and recognised that the battery is empty. Then I switched the battery and the hr values in the app were ok. Then I trained with the watch (s9pp) and the belt and got unplausible values after 10 min of running. Then I decide to change the soft strap. Within the next run I’ve got the same issues, bad hr readings.

Then I recognised the problem. When I connect the h9 belt with the polar app, the s9pp lost the connection to the belt. A reconnect of the s9pp with the hr strap solved my problem and would have done it, before I changed the soft strap.

Francesco Pagano

@marcrie So are you saying that the issue for you seems to be caused by the chest strap being connected to the Polar app and then to the watch?
I am quite sure that after my last experience with incorrect measurements I had just reconnected the strap to the watch, but I can try something more accurate

Francesco Pagano

@Swaddy61 It’s an interesting guess, but I wore the watch on my jacket sleeve so I imagine there really couldn’t be any HR reading from the wrist

cosme.costa

@Francesco-Pagano @Swaddy61 I do not know with Garmin HR straps but experience with polar H10 is that when you have strange values (on the watch or on a Garmin 530) is most of the times because of the strap, you can washmachine it and will see some improvements. In my experience when the battery is empty or very low it stops working.

What I can tell you for sure Is that Suunto doesn’t switch between HR monitors automatically, If the activity starts with the chest strap won’t switch to the watch OHR automatically, the same the other way around. You can test it starting the activity with the chest strap, remove it and you will see it.

Swaddy61

@cosme-costa You are right! Someone else on the forum had suggested it might switch back to the watch if the belt stopped, and as my Coros did that, it seemed quite likely. But I have tested, and you are right - it just stops!

So @Francesco-Pagano as the Garmin belt doesn’t appear to have a removable sensor unit we can rule out a ‘connector’, so that leaves 2 things to try - (i) wash the belt (check Garmin instructions!), and (ii) re-pair the belt.

Oh, and a third thing you could try - use some electrogel to ensure a good connection between the belt pads and your skin. I use Gadget Planet ABGYMNIC Conductive Gel - about €7 a bottle, and a bottle lasts many months using 3 times per week on the belt (you don’t need much). I used to get intermittent results before using the gel - so much more effective than just wetting the pads!

false

Oh, and a third thing you could try - use some electrogel to ensure a good connection between the belt pads and your skin.

From my experience - if hr belt is fine it works nicely even when it’s dry

false

@Mff73 I did my best

Francesco Pagano

I ran a new test today and something interesting came up.
I had the HRM chest strap connected to both my S9PP and to an old Garmin Vivofit watch so I could see my current HR on both. I started an easy run and at some point the Suunto watch again spiked from a reasonable ~150 bpm to over 170 whilst the other watch was displaying the expected HR, which corresponded to what S9PP on the pause screen.
This suggests me that Suunto watch is displaying a different value than what the chest strap is sending.
The funny thing is that this pretty much always happens at the same point, when I run a very short hill down and my pace and cadence increase for a few seconds. Today and previously it seemed that my “fake” HR corresponded to my cadence, so could this be a case of cadence lock?
In other cases when the displayed HR was way too low I can’t see any relation instead.

@Francesco-Pagano I’ve not heard of cadence lock with HRM pro…

isazi

@Francesco-Pagano while cadence lock is something that can happen with optical HR (because hitting the ground can create artifacts for an optical reader), I cannot imagine how this could happen with an electrode. Unfortunately I have not used a Garmin HR chest strap since 2019 so I do not know what is transmitted, if heart beats or inter-beat time (although I guess the latter).

Mff73

@Francesco-Pagano
Are you sure that your S9PP locked on the belt HR before starting the activity?
If yes, your tests may lead to think that your watch is using wrist HR despite what you think. But how to prove this

TonyG

@Francesco-Pagano

I had these issues all the time with 9 peak & suunto 9 baro, and did loads of experiments to try and work out what was happening but more importantly how to resolve or stop the issue happening in the first place.

https://forum.suunto.com/post/114542

ODo67

Hello!
I’ve had two Hrms. Neither lasted more than 6000 km (1 year and a half for me ️). I don’t think they’re designed to last any longer, especially with the non-replaceable strap. Since I switched to Suunto for my watch, I’ve bought a belt that costs half as much and has a replaceable strap!