Garmin Fenix 5s Heart Rate Accuracy Review

Side by side shot of the Fenix 5s next to the Forerunner 235.
Why does the Forerunner 235 perform better than the Fenix 5s when tracking heart rate?

There is no doubt that the hype surrounding the Garmin Fenix 5 series is pretty high right now.  You can already search Google and find dozens of reviews out there about this watch and the different series you can purchase.  There are multiple, upon multiple youtube videos (hundreds!) on the internet.  Most of these reviews are to sell you a product.  That’s how reviewers (including myself) generate money.  We review a product, provide an affiliate link for purchase, and get a small portion of the sale.  Well folks, the Garmin Fenix 5s does a horrible job tracking heart rate.  As it stands now, I would not buy it if wrist based heart rate accuracy is important to you.

Before we go any further, let me tell you about my affiliate link.  Yes, “link” in the singular sense.  I only fund myself through an Amazon affiliate link and I do it very poorly.  I have made zero dollars when we add up all the costs.  I’m many, many dollars in the hole.  I have sold 0 dollars of Garmin tech with Amazon affiliate links, even though I’ve invested thousands of dollars on their tech for review.  That means, I have nothing to gain here besides providing real experiences for the consumer. So, with that said, let’s begin.


Looking at the back of the Fenix 5s and Forerunner 235. We can see that the forerunner 235 has a decent protrusion where the elevate heart rates sensor is located while the Fenix 5s is fairly flat on the back.
You can see the back sensor on the Fenix 5s doesn’t bump out as far as the Forerunner 235.

The Fenix 5 series comes with a new optical heart rate sensor.  I truly don’t know if it is different since it is still named the “Garmin Elevate” but it IS different.  It doesn’t bump out like the Fenix 3 or the forerunner series.  It is fairly flush on your wrist so you don’t get that circular mark when wearing it tightly.  Whatever it is, or however it has been changed, it doesn’t do a good job.  I can’t figure this thing out at all and I did pretty well with a Garmin Forerunner 235 (235 Review Link).

Nested Reviews

This review will be nested in a full Fenix 5s review.  I would prefer to evaluate this watch in chunks (mostly because I have a full time job that pays my bills).  This article will be a branch article off the main Fenix 5s review that I put together (link coming soon).  This makes things much easier to digest, and allows people to dig further into areas they care about or skip the ones they don’t.

Wrist Based HR Tracking

Again, just looking at the difference between the Fenix 5s and the Forerunner 235 elevate sensors for heart rate.
Again, just looking at the difference between the Fenix 5s and the Forerunner 235 elevate sensors for wrist based heart rate.

Wrist based heart rate tracking is already a contentious issue.  A lot of the running watches and fitness trackers I use, do a pretty good job below 160 beats per minute.  Most wrist based sensors struggle reaching the higher heart rates and they struggle keeping an accurate track of your heart rate when there is some tension in your wrist.  So, there is nothing new here when looking at the Fenix 5s.  It performs just as well as it’s little cousin the Vivosmart HR built in 2015.  You can buy that watch for $105 on Amazon right now.  This is why I am disappointed.  Is there any watch that does a better job?

Who Does It Well

Yes, the Garmin Forerunner 235 does a pretty good job tracking heart rate.  You can see the results when I tested it out over a 6 month period (Forerunner 235 Long Term Review).  I even provide some tips on how to wear it properly when you run (just tighten the band a bit.)  Great performance is an expectation for the Fenix 5s.  I thought the “s” stood for SPORT!  How does a watch you can buy on Amazon for $280 outperform a watch that costs $599?

The Fenix 5s Heart Rate Tracking

Am I being hard on the Fenix 5s right now?  Yes, I am because I spent a lot of money on this watch and expected much more from it.  Especially, since the Forerunner 235 does a decent job tracking HR at the wrist.  Also, I would like to point out, that I moved the watch up and down my wrist during testing, tightened it, loosened it, wore it on the other writs, and wore it backwards on my wrist.  The results did not change.  So, let’s look at my results.

Indoor Bike Ride

My first ride was an indoor bike ride.  I connected my Wahoo TICKR heart rate strap to the Sufferfest Training Centre App and trained to a video.  I ran my Fenix 5s at the same time to capture the heart rate data.  This way, I could plot the data and see how far it was off.  I changed positions (on the bars, on the hoods, and in the drops) multiple times during this test and nothing seemed to give me an accurate report.

This graph shows a very poor performance of the Fenix 5s in regards to Heart Rate. I have the Wahoo TICKR on my chest and attached to the Sufferfest Training Centre App.
No matter what adjustments I made, the Fenix 5s Heart Rate was all over the place.

Folks, the chart above is a nightmare.  The Fenix 5s is pretty useless riding your bike inside.  That sucks, because it is one of the few watches that can pick up a power meter.  There are other implications also.  That cool feature where you can transmit an ANT+ heart rate signal from your Garmin watch, that’s never going to be used.  The data is inaccurate.  This means the capability to transmit heart rate data to an indoor cycling app like The Sufferfest or Zwift is pretty useless.  This also means transmitting heart rate to my Garmin 520 is going to be useless.  Let us look at the outdoor ride next.

Outdoor Bike Ride

Next, I took the Fenix 5s on an outdoor bike ride.  I connected my Wahoo TICKR to my Garmin 520 cycling computer.  I was in the drops, on the hoods, and at times I was dangling my arm off the bike trying to get the heart rate numbers to line up with the TICKR.  As you can see, it is a frustrating process.  Any clenching of your fist, or tension in the muscles will significantly drop the heart rate reading.  All of those massive drops in heart rate is when I gripped my handlebars tight to see what would happen.

This is a graphic of the Fenix 5s heart rate plotting agains a Wahoo TICKR connected to the Garmin 520. You can see it is not good. The Fenix 5s struggles and bounces all over the place.
As you can see, the Fenix 5s also does a very poor job tracking heart rate outside.

As you can see from the chart above, we can’t use the Fenix 5s riding our bike outside either.  This just doesn’t work well and you will get frustrated.  Yes, the Forerunner 235 also struggles on the bike, but it doesn’t struggle as bad as the Fenix 5s.  Okay, what about running, it has to be better at running right?

Indoor Run

I had high hopes here.  In this test, I ran the Fenix 5s on my right wrist, the Forerunner 235 on my left wrist, and then sat the Forerunner 230 on the treadmill connected to my Wahoo TICKR HR strap.  I did a run on an indoor treadmill because I felt I could get the most accurate readings possible.  The Fenix 5s performed about the same as the Vivosmart HR in similar testing (230 vs 235 vs Vivosmart HR Accuracy).  I was severely disappointed.

This is an indoor treadmill run with the Fenix 5s heart rate plotted against the Forerunner 235 and the Forerunner 230 using a Wahoo TICKR heart rate chest strap. The Fenix 5s performs much like the Vivosmart HR.
This test reminded me of the Vivosmart HR test, where I looked at performance compared to the Forerunner 235. I am disappointed to say the least.

You can make a case that the Forerunner 235 doesn’t do a very good job either.  Yes, it isn’t as good as a chest strap, but it is a hell of a lot better than the Fenix 5s.  I am really confused right now. Garmin should have been on to something with the Forerunner 235.  I am crossing my fingers now and hoping the Forerunner 935 performs just as well as the 235.   The Forerunner 935 is coming in next week, so I have the summer to build a nested review with that device also.  We will see.

Outdoor Run

Outdoor run?   I am reserving this for a firmware update.  I don’t want to waste anymore of my time showing how bad the heart rate function of the Fenix 5s is.  I’m really hoping this is a software problem and not a firmware problem.  Maybe I have a faulty watch?  I should contact Garmin and see what they say.  Is there anyone else that has noticed this with the Fenix 5s? (comment below)


In conclusion, I wouldn’t buy the Fenix 5s if heart rate accuracy is important to you.  I wouldn’t buy it if heart rate accuracy is sort of important either.  You are better off purchasing the Forerunner 235 because it does a much better job than the Fenix 5s for less than half the price.  That sucks saying that because I would love to sell a bunch of Fenix 5s watches on Amazon and make some money back, but I can’t, and I won’t.   I’m revising my statement here after talking to a friend.  It isn’t right to say you shouldn’t buy the Garmin Fenix 5 because heart rate function doesn’t work so well.  The HR function doesn’t work that well on the Fenix 3 either, but people love that watch.  They love it because it does so much more than just track heart rate at the wrist.  I cannot disregard the fact that this is the most advanced watch you will ever buy.  I’m actually really enjoying all the extra features on this watch right now and will gladly put on a chest strap during an activity.  So, I’m revising my statement because of good advice.

You can use the link below and buy the Forerunner 235.  That’s a watch I stand behind.  Also, you can click on the Amazon link at the top of the right sidebar.   ANY purchase you make helps keep me independent and free of influence.  Buy food, buy clothes or paper towels; any purchase helps.  When my final review is done, I’ll have everything up on the Compare Equipment Page also.

Purchase the Garmin Forerunner 235

Purchase the Garmin Fenix 5 




8 thoughts on “Garmin Fenix 5s Heart Rate Accuracy Review

  • July 30, 2017 at 3:46 pm

    I have been using the Garmin 5S for a couple of months. I have noticed the same problem with the optical HR monitor and it is the reason I read your review. I thought maybe I had a faulty one. I have only been paying attention during outdoor bike rides. I noticed that on hill climbs where I know my HR should be in the 155-175 range depending on my level of exertion, the optical HR on the Garmin 5S will only ready somewhere between 100-120. If I wear a Garmin HR strap, the watch will connect to the strap no problem and will have the correct reading. i have called Garmin and they said they haven’t heard of similar problems and told me to wash the watch with water and tighten the strap. I still would have bought the watch as the other features are great but am a bit disapointed in the optical HR sensor.


    • July 30, 2017 at 6:43 pm

      Hello Martin, I heard the same thing from Garmin. I think most watches don’t do a good job with the wrist based Heart Rate except the Forerunner 235. I have someone testing the 935 right now and it looks like it might do a slightly better job. I do like all of the options with the Fenix 5s though. I should be testing the Navigation and hiking piece here in August. I just had to get familiar with Base Camp and all that so I do it the right way.

  • August 29, 2017 at 6:45 am

    Hey! I have recently bought this watch and was surprised when my heart-rate reading for an intensive HIIT class and all out MTB ride was pretty low. Turns out no, I had not got super fit recently.. it must be the watch (haha) and my suspicions were confirmed (and I was rather dismayed) after reading your article. I did notice however that it was reading my heart rate well when worn under my wetsuit for surfing. So I tried putting a basic compressive bandage over the watch (simulating the wetsuit compression and occluding light around the HR sensor) for my HIIT class and low and behold I started getting a much more accurate depiction of my HR! I haven’t tried it yet with MTB riding but I thought I would share this mini break through for you maybe to try?! It’s not perfect but I’m happy enough with this simple solution.

    • August 29, 2017 at 7:46 am

      That is an interesting observation Jane. I did test with a very tight band and a very lose band and it didn’t have much of an effect. I wonder if covering the watch is keeping sunlight out and then enhances the measurement on the wrist. Very interesting observations.

  • November 15, 2017 at 9:09 am

    Good to read your review. Mine is actually reading high, not low. My easy runs usually result in a 125-130 bpm when measured with a Fenix 3 with chest strap. My new Fenix 5 was showing around 160. There’s no way this can be right. I did the same as you, tight, loose, back of my wrist etc. This was also running in darkness, so that rules out sunlight as a factor. Very disappointed because I love the Fenix series, and was hoping to be able to ditch the chest strap. Obviously not!

    • November 15, 2017 at 10:38 pm

      Unfortunately my theory and technique has since been foiled and I am too very disappointed with the inaccuracy of the wist HR as it still reads very low on me. I have reverted back to my old chest strap which is frustrating!

  • January 11, 2018 at 5:13 pm

    I’m late to this but I only got the Fenix 5S as a Christmas gift. Thanks for the in-depth review on the HR tracking; I am relieved that it’s not just about my small wrist. Coming from Vivocactive HR and having been eyeing this watch for a long time, I was very disappointed with HR tracking. I wanted a sports watch that can function as a smart watch while being aesthetically pleasing (relatively) but this doesn’t seem to do the “sports watch” part of the job well.
    It’s going back but I’m curious to know if there’s something this watch does well from the perspective of being a sports watch.

  • January 11, 2018 at 9:44 pm

    I too came to this post after becoming frustrated with inconsistent performance from the OHR on my Fenix 5. Some activities seem to read reasonably well while others are way too low. I do not get consistent results within the same activity either. Watch is always clean and tight. It does seem to perform better during activities that don’t strain the wrist, but not always. Basically can’t trust that I’m ever getting good data.


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