Is your HRM accurate? — TomTom Community

Is your HRM accurate?

Not_dead_yetNot_dead_yet Posts: 2 [Apprentice Traveler]
My TomTom3 runner watch seems to give heart-rate readings when running which are consistently too high. I can easily get readings which are 15% higher than my (220-age) maximum, and even on a slow jog the watch will say I am working at 95% of max.
I have compared against a Garmin watch (with a wrist sensor), and a Polar (using a chest strap). Both give lower readings than my watch.

I have a suspicion that the watch is getting confused by readings from the step sensor, but I've not worked out how to turn this sensor off to check.

Has anyone else seen this problem?


  • tfarabaughtfarabaugh Posts: 16,191
    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. 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. 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.
  • Not_dead_yetNot_dead_yet Posts: 2 [Apprentice Traveler]
    Your reply agrees with my thoughts, and explains why dropping speed doesn't help, as I'm still running at the same cadence. It sounds like disabling the signal from the step sensor would help. TomTom - can that be done?
  • MachMach Posts: 89 [Outstanding Wayfarer]
    Normally when you run slower, your cadence also drops a bit. For me it's 170 at 6:00 min/km and 180 at 4:00/km and up to 187 at 3:00/km .

    I've seen the optical HR sensor losing the plot in the middle of hard interval session and at the end of a long run, when I'm really warmed up, but I've also seen the HR sensor working correctly even at -10C at the beginning of my run when I was not warmed up at all. I guess it's all a matter of the algorythm which should figure out and distinguish cadence from HR. If my max HR is 186, then it's pretty obvious that my HR in the first minute of the run cannot be 180.

    Whether the step sensor (pedometer) can be disabled is a good question, yet I can imagine the pedometer is also used for calculating current pace, so disabling one thing may affect the other functionalities.
  • tfarabaughtfarabaugh Posts: 16,191
    You cannot turn off the accelerometer, as that is part of the pace calculation and other items. It wouldn't matter anyway as this is not what is causing it. It is not an electrical signal from the accelerometer interfering, it is the signal (maybe pattern would be a better word) from your feet hitting the pavement that is the issue. It is creating a rhythmic pattern that the watch is picking up as it is overriding the HR signal.
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