Fix *optical* HR and chest strap HR issues – Troubleshooting Garmin, Polar, TomTom, Suunto

What! A heart rate of 280bpm, that can’t be right can it? Oh hang on a minute now there’s no reading at all.

Most of you have been there with Garmin HR straps. It’s annoying when the readings are wrong especially if you train by heart rate. Luckily you’ve just bought an expensive, optical HR device for your wrist – or maybe even for your upper arm or ear. Let’s say ‘wrist’ for now. Surely new technology can only make accuracy better?

suunto spartan sport whr valencell

Nope. More than likely the optical situation will make matters worse for the general population and their optical HR woes.

Anyway DC inspired me to update an old post of mine with lots of lovely 2017-opticalness.


I thought I knew what I was doing with chest straps. I didn’t have many problems that weren’t easily solved by buying a new one. Conversely I might wear one optical heart rate device with no problems for a while and then a new model arrives and I wear it in EXACTLY the same place and do the EXACT-SAME sporting things…but the HR readings are rubbish.

There is a lot going on here and I’m not convinced that anyone quite understands why sometimes things just don’t work with optical HR.

2x Epsons Optical Sensors

You’ve probably read about these:

  • oHR can sometimes be tricky on darker skin
  • oHR can sometimes be tricky on hairy skin
  • oHR can sometimes be tricky if you have a higher fat content on your lower arms
  • oHR is affected by blood circulation (it takes the reading from bouncing light off blood…so there must be blood)

So the solutions are simple: lose weight; don’t get a tan/change ethnicity; cure Raynaud’s syndrome; and shave your lower arm hairs! Not very helpful, sorry.

MIO Fuse Review - Optical Sensor
MIO Fuse – Optical Sensor

The quality of the sensor is important and these are some of the factors that go into making a good piece of hardware:

  • Colour(s) of the LEDs
  • Spacing of the LEDs
  • Shielding the shone and received light from interference of other light sources of similar wavelengths

But, perhaps even more than that, the watch/sensor manufacturer will most likely have to add a mathematical algorithm (software) to deal with: the swinging of your arm; the flexing of your wrist; and the particular bounce-type of whichever sport you are doing. Yes the algorithm will probably vary from sport to sport.

1st TIP: Use the right sport profile or just stick to the sport profile where it seems to work best

 Example or errant optical HR readings from Garmin 5X

You will no doubt have read the user manual that came with your errant watch. It will likely say something like “wear the watch 1cm from the wrist bone and wear the strap tight but not too tight to leave mark”.

2nd TIP: Wear it tightly 😉 and If practical wear it further from the wrist.

But I’ve found that even when wearing it in the ‘right place’ (1cm from your wrist) that the blooming thing can slip down back to the wrist. Yet, as alluded to earlier, with some devices this causes no problems but with others it does.

3rd TIP: Try the other arm to find a bit more watch-strap friction

Polar Unite ReviewIn some of my more ridiculous moments I have pounded the streets of SW London wearing several watches. This is not a good idea. As well as the watches banging into each other and ruining the optical HR signal I have heard that it is possible for one optical LED from watch to affect the sensor on another watch and they do not even have to be next to each other/ maybe the light goes within the body or directly through the air. Someone with a grasp of physics can clarify that one for me.

4th TIP (just for me) only wear one optical HR device per arm or even just one in total.

So with all this ‘pounding’ going on, what personal factors could make that pounding worse? Maybe if you have a heavy impact when you run that could be a factor but maybe even the weight of the watch could be a factor as a heavier watch could move about more than a lighter one? This might explain some of my recent Garmin Fenix 5X woes – beautiful watch but heavy and I’ve not found the oHR as good as other, earlier Garmins like the 735XT.

5th TIP: Run lightly and avoid bumps in the road

Garmin 735XT Optical ELEVATE
Garmin Elevate – Pretty Accurate In My Experience

More recently I’ve seen some issues with optical HR devices seeming to take 15 to 30 minutes to ‘warm up’. Maybe it’s me warming up 😉 and getting the blood flowing.

6th TIP: Cover every angle of warming up – from a proper physical warmup to wearing the device before your exercise to ‘get it warmer’ and maybe even try recording a pre-run 15 minute dummy session.

That’s probably covered most avenues. If you have any other suggestions MANY other people will gratefully receive them. Thank you

7th TIP: Buy a chest strap 😉


But on that note there are problems with chest straps too. I generally don’t have any problems with straps less than a year old. For some of the older Polar/Suunto/Garmin straps it was often either the STRAP (not the pod) or the BATTERY that was the cause of the problem rather than the physical ‘HR ‘pod’.

Firstly there could be a fault with your STRAP and/or your heart rate SENSOR / POD. I think that is unlikely in most cases where you have relatively new equipment.

Secondly if you have ever used a Garmin HARD strap you will probably have never found any problems. So that shows that the problem probably does not lie with the watch. If, like me, you may have bought a POLAR soft strap to which the GARMIN POD fits you will probably found the same level of HR spikes and dropouts in similar circumstances. Therefore this suggests to me that there is nothing inherently uniquely wrong with Garmin’s design.

Garmin HRM-TRI (HRM-SWIM) Review
Garmin HRM-TRI (HRM-SWIM) Review 4iiii Viiiiva Wahoo TICKR-X HRM-RUN

It’s just that soft straps for some reason are more prone to the sort of behaviour we are talking about. Why? If you look at the reverse of the strap you will see that the smooth ‘rubber’ contact area may be smaller on a soft strap.

This post is an updated version of (this) post from 2013:

Yesterday I had a turbo session indoors. Nothing too hard but a bit sweaty nevertheless. Immediately afterwards I went for a slow run in the freezing cold. Within 5 minutes I had incorrect HR readings. I had stopped sweating and some of the sweat already there had dried out. This to me VERY strongly suggests that the problem is related to the contact between the body/chest and the strap.

In really cold or really dry weather you may well find you are more prone to spikes. This could be because both hot and cold weather can have less humidity (humidity might be a factor). Or it could also be the case that when really cold you might not sweat much or when really hot and you are not trying much the sweat very quickly evaporates.

Similarly in early Spring or late Autumn/Fall when I am wearing thin clothing and cycling quickly I find some instances where I lose a HR signal and attribute this to the air movement causing all the sweat to evaporate and dry my skin.

Polar H10 H7 suunto smart belt movesense garmin hrm-tri hrm-swim

Either way a wet strap helps.

So if you lick your strap before any exercise you will probably find an improvement.

8th TIP: Lick it!

Polar H10 H7
Lick the shiny black rubber pads on the rear of the strap

Furthermore if you thoroughly wet the strap, you may find yet more improvement.

Garmin recommend that you use medical grade gel. I bought some and found that saliva was just as effective BUT saliva would more readily dry out in certain conditions.

Well 30 minutes after posting the original article I got this from Cy Gearing on FB:

Cy Gearing :: I use the garmin soft strap and use a physio gel. I don’t sweat a great deal so had issues, but been using the gel for 3 months now without dropouts. It cost the vast sum of £3.05 for 2 x100ml bottles and you need so little that I’m sure they will last at least a year!

So this I think backs up my assertion that it is a contact problem rather than static or faulty devices. Although Cy has obviously found that gel makes a significant improvement (well if 100% counts as significant!).

UNUSUAL (9th) TIP: Take out the battery and put it in the wrong way. Then put it in the right way.

However static might be a cause. BUT two different materials are required for static to happen (physics). This could be different shorts and shirt. Or it could be the soft strap and your shirt rubbing together. It might also be linked to static from body hair. I’m not convinced about this explanation but it is possible. I still have problems when ‘topless’ on my turbo. Static absolutely CANNOT be the cause in that scenario. Although it might be a contributory factor in other scenarios.

Finally you need to wear it in the right place! The centre of the pod goes over your solar plexus just below your rib cage. This is easier said than done for some people who find it extremely hard to get the chest strap to stay in the right place and, in fact, one of the reasons why lots of people  buy the optical HR devices we started talking about at the top of the post!.

10th TIP: Wear it in the right place or buy an optical HRM…oh dear 🙂


Reader-Powered Content

This content is not sponsored. It’s mostly me behind the labour of love which is this site and I appreciate everyone who follows, subscribes or Buys Me A Coffee ❤️ Alternatively please buy the reviewed product from my partners. Thank you! FTC: Affiliate Disclosure: Links pay commission. As an Amazon Associate, I earn from qualifying purchases.

25 thoughts on “Fix *optical* HR and chest strap HR issues – Troubleshooting Garmin, Polar, TomTom, Suunto

  1. Other than battery low voltage failure, I presently have been using Spectra 360 Electrode Gel. It is cheap and easy to put on the Garmin and Suunto HR chest straps. With the Suunto, I get almost no dropouts or high readings. Bluetooth. With the Garmin, I get high HR when sprinting at the end of my runs. Ant +. My average HR is within two beats between both watches.
    I wear both chest straps for all my runs. With Garmin strap under my pecs and the Suunto strap about two inches over my pecs. Seems to work well. I also shortened any thick hair over where the pads are touching my skin.
    I am too cheap to buy a watch using OHR. My 910XT and Ambit3 Sport are good enough for me.
    My limit is under $200. for a used or refurbished sports watch.
    And with the STRYD Foot Pod I get POWER using the 910 in Bike mode and Ambit3 in Run Mode.

  2. The Suunto and the Addidas ( same snap spacing as Garmin ) have different snap spacings.
    Also Suunto uses Bluetooth while Addidas/Garmin use Ant+.
    Is there a dual strap that would accommodate both HRMs ??

      1. Thanks for the heads up. I guess two straps will be my norm for now.
        Back to the original post about OHR. If you put the band on tight, I believe within a year the non-buckle watch strap will begin to tear and break. Replacements watch straps from China are cheaper then from Garmin or Suunto. My 910XT is in its 2nd strap.

      2. good point. a strap like the ‘plastic’ fenix 5 one should be ok but something like the rubbery Spartan ones I suppose will be limited in their longevity

  3. Try a dual sensor Decathlon Kalenji CardioSmart sensor (made by Cardiosport) without strap ref. 3608429896289 19.90€, there is also a version with strap for 35€

  4. I don’t think i’ve ever had an issue with HR while using ANY of the chest straps I own (H10,HRM Tri,Tickr X) and I use the Spectra 360 as well. I think I paid 15 bucks American for like 9 bottles worth. A dab on each pad and you are good. As for comfort, the HRM-tri and H10 are super comfortable to wear (the H10 is the more comfortable of the two in my opinion) the Tickr though, not so much.

    As for reporting, I’ve used each on the same HIIT workout and found the H10 and Tri to be nearly identical, with just natural variants to my health. Each come off smooth on the chart (I use the Graphical HR widget on my F5 during workouts). The Tickr reports the same eventual information at the end, but is a blocky mess during the routine.

  5. Is there any evidence that oHR deteriorate over time? I’m using a 735xt and I’ve been pretty happy with it but of late the readings come in very high. When comparing it directly with a Vivosmart HR+, the readings come in ca. 30 BPM higher on the 735xt. Is this a known issue? I’ve only had the watch for a year or so.

      1. Thanks for the reply. I was wearing 735xt and Vivosmart HR+ during the same workout so I’m still a bit surprised they come in with such a big difference. I will try with breast strap tomorrow to get a better picture. Thanks again!

      2. Hi there,

        I have a FR235 which has an oHRM – I have the watch for about 3 years now and over the last month, the HRM has been going completely nuts! A few days ago, I did an easy run and it measured my HR at 220 bpm (I almost died when i saw the reading!) – I did a manual pulse test and my HR reading was a touch over 120 bpm.

        I then converted to the Garmin chest strap and found that it picks up an accurate reading which is in line with my normal readings.

        I have been searching online to see whether there is a recent software update for the oHRM alternatviely, a way in which it can be recalibrated but nothing pops up!

        Any ideas (short of continuing with the chest strap)?


  6. I wanted some watch with oHR for occasional bare-breast runs (I’m a man, ok) and I can’t get over myself wearing chest strap in these occasions. Also swimming. So ended up with Polar Vantage M.

    What a rubbish (read: sh**y) HR I’ve got on it compared to the chest strap 🙁

    Nevertheless I’ve came up with a wonderful reviews of Polar’s OH1. Hmmm… same technology, better results?

    But OH1 is worn usually on the upper arm or middle forearm. Go figure…

    There’s nothing strange, that wrist based OHR is usually worse than better. Because wrist is quite a bad place for readings: there’s not too much to read from.

    Wear the watch where’s there more meat.

    Tried it. Not 1 cm from the wrist bone. Full 5 cm. Middle fore arm. Upper arm! (Crazy place to wear a watch, surely, but, boy, can it provide wonderful results!)

    Swimming HR wearing a watch 5 cm above wrist bones increased in accuracy dramatically, it became useful. I’ve lowered my heart rate zones by 10 to reflect my felt effort better and now it is a nice supplement to overall training. However: tried wearing on upper arm and then Vantage M failed to detect swimming strokes 🙂 Also it failed to detect them worn on the opposite side of the wrist. That was to be expected.

    Wearing a watch on upper arm (i.e. biceps) was not that bad, as I’ve though. If presbyopia is already prominent… well, wear your reading glasses when running 🙂

    The issue is straps. I don’t understand, why the hell sports watches have silicon straps mainly. I’d prefer the same elastic strap like the one of OH1. It would solve lots of problems.

    I made a DIY long (for watch enthusiasts: classic pilot style worn over the leather jacket) strap from two woven nylon straps, as they can be daisy chained for my biceps-run.

    Dear 5krunner, would you try and (re)validate this? 🙂 I.e. wear Polar watch on upper arm simultaneously with OH1?

    Of course, YMMV. This approach worked for me. Not going to work for everyone. But I’m pretty sure, that more muscle provides better blood flow readings.

    1. hi
      it’s different tech and different results
      more importantly its worn in a different position.
      there are many reasons why OHR is not great (I frequently mention them on this site).
      but the main reason is that there are too many wrist movements and OHR cannot then distinguish the blood movements
      compare to a chest strap where an electrical signal is measured…much easier.

      there are less upper arm motion artefacts. so, yes, you are correct. wearing a wrist watch on the upper arm should gieve much better (like 98-99% of reality) results.

  7. I was in such despair! Thanks for the great article and tips. Can you provide a link to the medical grade gel you are referring to that keeps the strap wet? I think that’s my main problem. Thanks!

    1. i have used SONOGEL. it;s what physios/masseuses use. i don’t think it usually makes that much difference for me.
      even if you don’t think you sweat there should be sufficient very mild perspiration for your strap to work
      the hrm could be old or the battery could be old.
      the hrm could pushed lower than the ideal position by your female morphology
      body fat content can make a difference

      perhaps consider an arm band like the polar OH1. That should be accurate.

  8. I seem to have a problem with heart rate straps in general. I noticed my HRM-Tri giving results that didn’t seem consistent with my RPE, so I started wearing both the HRM-Tri and the Scosche Rhythm+. The Rhythm+ matched my RPE, and the HRM-Tri didn’t. I tried tons of troubleshooting tips (licking, using water, using a lot of gel, using a little gel, tightening the strap, rotating the strap, exchanging for a new strap, wearing cotton, not wearing a shirt), but the results remained consistently unreliable.

    I then busted out an old Polar H7 and compared that to the Rhythm+. The data from the H7 was literally unusable with oscillations about 10bpm above and below my actual heart rate (but at least generally trending with the Rhythm+). I thought the H7 was busted, despite the shiny new battery, but when I used it for a trainer ride today, it aligned almost perfectly with the Rhythm+. The HRM-Tri also seems to work fine on the trainer.

    The chances that three chest straps would be bad, including one brand new and one less than 6 months old seem infinitesimal – especially when they work for non-run activities. It seems like the way that I run is a problem for chest straps?

    Any tips outside of the standard Garmin support?

    Rhythm+ vs H7 Bike:
    Rhythm+ vs H7 Run:
    Rhythm+ vs HRM-Tri Run:

    1. hmmm
      a pic on your site seems to rule out you being overweight.
      is the pod on the bit where your ribs meet. solar plexus or whatever its called.
      i doubt its how you run
      a passing thought: maybe it could be something wierd firing in your heart itself ie electrical? go and see a doc to get an ecg
      Heart arrhythmia? show the doc your charts
      the optical hr senses are NOT electrical but instead based on blood flow

      PS on the treadmills that I use they churn out interference as my BLE audio on my 945 works poorly (worse than when running)

      1. If it was a heart-related issue, I’d expect it to be visible for all types of activities, not just running (a heart issue was also my conclusion, until my wife, a cardiac nurse, convinced me otherwise).

        My treadmill doesn’t have a Bluetooth radio on it (just the 5mhz strap support), so from a radio interference perspective, the trainer would be more likely to cause interference than the treadmill, unless there is some other interference that the motor of the treadmill makes (but again, it’s the same issue running inside or out).

        As far as I know, I’m wearing the strap correctly:

        Just for funsies, I’ve been recording multiple heart rates on all of my activities:
        This outdoor run took 55 minutes for the two to get in sync:
        This indoor bike was pretty good:
        This indoor run had issues with both HRMs:

        Garmin support has thrown up their hands, which I can’t blame them for. And I feel confident enough in the Rhythm+ so I’ll just use that going forward, but it’s pretty frustrating having a $120 strap that can’t be relied upon.

      2. yes i would expect it on all activities.
        having said that I had some anomolies linked only to running and I ended up seeing one of the top cardiac consultants in the uk….

Comments are closed.