Heartrate isn't accurate

Softiest
Softiest Registered Users Posts: 2
Apprentice Traveler
edited January 24 in TomTom Sports
Hi!

I have Spark 3 cardio watch and I've been using it now for 2 months. I understand that if I do exercises that include using of forearm muscles the heartrate can be measured lower than it actually is. But the same problem comes also when for example running sprints, which really doesn't involve THAT much forearm muscle use than many other activities..

The watch sometimes also measures heartrate to be greater than it actually is, which I can't understand. For a one hour calorie consumption the watch reports to be 550 kcal, and it's definitely too high. Is there something I can do? Can the watch be broken? Now it's kind of useless because the the inaccuracy.

Comments

  • tfarabaugh
    tfarabaugh Posts: 16,943
    Superuser
    There is an additional issue with optical HR beyond low HR. You can also get spikes in HR due to the watch either losing the pulse signal and locking onto another signal, like cadence, or the cadence simply overpowering the pulse signal. 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.

    For the 550 calories an hour, is this during an activity or are you referring to the activity tracker (which will also take into account sports activities in its totals)? 550 calories an hour while running is reasonable, but 550 calories while sitting around is not, I agree.

    You can always try a factory reset but I doubt the watch is broken, you are just seeing the limitations of optical HR for tracking of sports activities. It is a mixed bag of accuracy. I personally only use the optical for running, cardio and indoor cycling. For weight training, rowing and outdoor cycling I stick to a chest strap.

    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.
  • Softiest
    Softiest Registered Users Posts: 2
    Apprentice Traveler
    Thank you very much tfarabaugh! Yes, this helped to clear it up to me. I might need to think of getting the chest strap on the side as well.

    The 550 calories was during an activity and it was during a very low intense training, so I figured that it somehow read the high spikes in HR as if I was doing something more intense that I really was, so that might have caused the calorie amount to be higher than it should be.
  • tfarabaugh
    tfarabaugh Posts: 16,943
    Superuser
    Softiest wrote:
    Thank you very much tfarabaugh! Yes, this helped to clear it up to me. I might need to think of getting the chest strap on the side as well.

    The 550 calories was during an activity and it was during a very low intense training, so I figured that it somehow read the high spikes in HR as if I was doing something more intense that I really was, so that might have caused the calorie amount to be higher than it should be.
    It bases calories directly on HR so if the HR spikes, so will the calories, unfortunately.