Posted by: Ian | February 12, 2012

Fixing wrong Garmin Heart Rate readings

As I’ve written before, my Garmin 800 routinely shows stupid-high heart rate readings. I used to notice this most frequently when I started to cycle and before I was warmed up enough to build up a sweat and/or when I was bombing downhill at high speed. Increasingly, it just gives stupid-high readings all the time. By “stupid-high” I mean readings in the 200-250 range, even when I’m not exercising. Finally, I’ve worked out what the problem is and how to fix it.

Before getting to what the actual issue is, I’ll cover briefly some of the alternative possible explanations that I considered. The most worrying was that the problem wasn’t with the Garmin but with me: maybe I had some weird kind of tachycardia. I never really thought this was the case, although I was a bit freaked out when I did the analysis that produced this chart:

The blue line shows my average HR readings from my rides, while the red line shows the max HR for each ride. You can see that the max often gets well into the 200’s. What concerned me was that the frequency with which this happens seems to increase dramatically to the right of the vertical black line. This line marks the date on which I was knocked off my bike and broke my wrist (and had an operation to fix it). Go figure.

Well, I did go figure and wondered (theory #2) whether the accident damaged my Garmin. I tested this by taking my HR reading using my old Garmin 500 instead of the Garmin 800. Unfortunately, I got the same stupid-high numbers. This effectively eliminated the theory that the fault lay with the Garmin 800 unit itself.

While I never really bought into the tachycardia theory, I could only discount it when I got some proof that other equipment gave saner HR readings. I found this (a) when I had a metabolic assessment, which measured my HR max as 178 bpm, and (b) when I went on a gym bike that measured my HR through metal pads on the handles, and which also showed normal human HR values throughout an intense session.

Having ruled out both the Garmin unit and my heart as potential sources of my stupid-high readings, I turned (theory #3) to the way the strap sits on my chest. I tried re-positioning it, dampening it, putting it on backwards, putting it on upside down and applying electrode gel, all of which were recommended at various internet sites and none of which worked.

Finally, I turned to the strap itself. I have the “premium” strap that came with my G800. Brian from Bicycle Chain found a procedure for resetting the plastic unit that houses the battery and I followed this (approach #4). This also brought no improvement. However, Paula has the same strap that she uses with her Garmin Forerunner 610 watch. When I tried this I had my first sensible HR readings, possibly ever, on the G800. Sitting around in the lounge using Paula’s strap I had a HR of around 50; using my own strap the same G800 unit recorded values approaching 200. Furthermore, by trying all possible combinations of my/Paula’s strap/battery unit, I learned conclusively that there is no problem with the plastic unit that holds the battery but that the fault lies in the strap itself, presumably in the ribbon within the fabric (ta-dah!) that connects the battery to the sensors. Some kind of fault in the connection there would explain why the problem has become worse over time.

Having firmly established this as the cause, Bicycle Chain are trying to get me a replacement from Garmin.

Using the Garmin with a functioning HR strap is fantastic: I can do HR-based exercises properly now. While the power-based sessions I’d done on the turbo recently are okay for strength development, they can’t replace the anaerobic interval and lactate threshold sessions that I’d picked up from my metabolic assessment.

Here’s the session I did yesterday on the turbo using Paula’s strap. First, I have two blocks (20 mins and 25 mins) at around my lactate threshold, which I can do now that the HR values don’t jump all over the place. Then, when I had a final 20 minutes in which I tried to get my HR to an upper target and back down to a recovery level as many times as I could, I was able to get in more cycles because I wasn’t getting held at stupid-high values at the top end. I can now actually use the Garmin properly as a training aid.

I also now have (courtesy of Brian at Bicycle Chain) a solution to the other Garmin problem that I reported recently, when I lost a intense training session and my Garmin 800 hard drive could no longer be read by a computer. Apparently, Garmin posted a firmware update in which they forgot to package the software component responsible for hard drive connectivity. There is a fix, which Brian installed for me; I’m relieved that it was even possible.



  1. Hi Sevi. Good to hear. Since writing this I’ve done a lot of analysis with a cardiologist on heart rate data taken from Strava. If you’re interested check out and hit the orange Connect button. Ian

  2. Oh man! I am very glad about this article because it describes my journey with a garmin fenix 3 amost down to every single thought and measure taken. Only difference that I spent a lot more time with worrying about my heart instead of gear.

  3. Hi Jenna. That’s very interesting – thanks. I’ve been doing a lot of analysis recently on high reported HR during activity in conjunction with a cardiologist. You can find it at Clearly, strap errors are a problem and mask what may sometimes be arrhythmia.

  4. I had the same problem which started about 5 months ago. I had readings all the way up to 115 BPM which did not correspond to the amount of effort I was exerting at the time.
    After reading this article I purchased a new strap on eBay and voila, all my readings are back to normal……… Item:

    • That should read 215 BPM…………

      • I’ve had a Garmin 800 for some 4 years. The heart rate monitor worked well until I had to install a new battery, after which all the readings were mostly over 200 bbm. I ended up cutting the strap between the 2 snaps, refastened the monitor and everything was miraculously back to normal. My thoughts are that after a lot of wear the strap itself between the contacts becomes conductive. A new stronger battery was enough to put this second electrical pathway to use screwing up the monitor readings.

  5. I have the same problem and will try the strap fix. I really appreciate the thoughtful evaluation of options, they are similar to what I’ve been testing but I wasn’t as rigorous!

    • Glad it helped. If you have the same trouble I’d recommend first washing the strap (ex the part with the battery and transmitter) to see if that fixes it, and, if not, get a new strap. If you’re getting a heart rate reading > 10% higher than your established max you have a strap problem.

      • Got the same problems during our race this week-end. The first hour, where thing were going in normal pace in the peleton, I reached heart rate at 225-235 bpm at the display. I know me self due to this, and was not during more than 82-85%. (max at 200 bpm).
        The last hour of the race was without stubid peaks, but small “jumps” at 5-15 bpm at the time. Normally you can go at steady pace, have a cip of cold water, then drop 2% in HHR and back again, no sudden peaks/drops. I have had Edge 800 for a year. The most stabile thing until now.
        Your expirence sounds like, I have to buy a new strap.
        KR Uffe DK

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