Spark 3 Cardio showing ridiculously high heart rate

desertman Registered Users Posts: 6
Master Traveler
edited January 24 in TomTom Sports
I'm running (or better: jogging) since about 10 years about six times a week on a 3 1/4 miles long mountain trail close to my home. Until recently I used "conventional" heart rate monitors with a chest belt (first from Casio; the last three or four years from Polar). All these years I always kept records of my time and my average, maximum, and recovering heart rate. I know very well which heart rate to expect at which point on my run.

I bought the Spark 3 Cardio mainly because I wanted to get rid of the chest belt and still be able to check my heart rate. I'm using the device since a couple of days. I like that the device shows the current heart rate during the run in big numbers. I'm wearing the watch quite tight; it cannot move sideways or up and down on my wrist during use.

However, my Spark 3 Cardio shows ridiculously high heart rate numbers during the first third of my run. It starts out ok for the first 6 or 7 minutes of my routine when I'm still just walking. But as soon I change over to running the heart rate monitor goes berserk and soon jumps to numbers between 160 and 180 in places where I usually have between 115 and 125. Then, after about the first third of the run, the heart rate monitor slowly becomes "normal" and shows my usual numbers - including during the difficult parts of my run where my heart rate is usually reaching 140 or even 145. At the end of the run the device also shows a normal recovering heart rate, and the strides per minute (something that the previous devices did not record) are consistent and seem to be correct.

What's not working correctly is the heart rate monitoring during the whole run, and that is the most important function for me on this device.

Is the poor heart rate monitoring normal for this watch, or is there something that can be done to fix it? Thanks for your replies.


  • tfarabaugh
    tfarabaugh Posts: 16,935
    Spikes in HR are generally from poor blood flow producing weak pulse strength, so the watch reads cadence instead. This is most common in running and is particularly apparent early in a workout or during a non-intense workout when you are not warmed up or when you are doing sprints with very high effort. You have to think of the optical heart rate as an algorithm that is attempting to track a signal in a set frequency range (30-230 or whatever it uses). If the pulse signal is weak it latches onto the next strongest rhythmic signal, which is your cadence in running and the vibrations of the bike in cycling. For most people who experience this while running it spikes to around 180-200 bpm which is also the average cadence people run at. Additionally, each person has a different HR signal ‘strength’, depending on a range of factors, so some are prone to get it more than others. But usually their signal strength is lower for the first 5-10 minutes until they warm up properly. So in that time, it is prone to latching onto cadence, which is a common fault with all optical HRs, unfortunately. Optical HR also can tend to lag in measurements, so if you are doing intervals it can take a but to catch up so it shows high HR during the rest periods. If you notice it while it happening you can try moving the watch a bit or briefly pausing your run so it loses the cadence reading and latches back onto HR, which I find usually corrects it. I generally pause the watch, stand still for 20-30 seconds and will see it immediately start to drop. Once it gets into a more reasonable range and the pulse reading stops dithering (dithering is when it is not getting a good signal and it is a lighter grey in color) I start up again and it stays true for the rest of the run. You can also try switching wrists and the position on the wrist. I find I got better readings on my right wrist over my left and some people find they get better readings if the watch is on the inside of the wrist rather than the outside. It also helps if you warm up a bit to get your blood moving and your HR up so it is producing a strong signal. Play around with it and see if any of this helps you. The challenge for the manufacturers of optical HRs (and this is a common issue with all brands, my Scosche also does it) is to figure out how to factor out the other "noise" that is overriding the pulse signal without also factoring out other important data.

    I hope this helped answer your question. If so, please mark it as a solution so others can look for it if they have the same question.
  • desertman
    desertman Registered Users Posts: 6
    Master Traveler
    Thanks. That explains the workings of such an optical heart rate monitor very well. I will experiment with a pause today.