Incorrect heartrate

scubajorgen Registered Users Posts: 12
Outstanding Explorer
edited January 24 in TomTom Sports
During running the Adventurer indicates a heartrate of about 140 bpm. This seems fair since when I measure my pulse during 10 seconds I find 13 beats, which corresponds to ~142 bpm.
However, sometimes the heartrate as indicated by the Adventurer drops. In the next example when I started running up a hill the heartrate value dropped (I would expect an increase due to the increased performance). After resting on top of the hill, apparently the Adventurer appears to 'lock' again, showing a more plausible reate of 150-160.

Even if I take the watch of my wrist, it keeps indicating a heartrate of ~100 bpm!! This does not make sense to me.:?
I would prefer an indication that there is no heartrate value i.s.o. an erronous value. If I remember well (not sure), a previous version of the software did this...


  • SamLars
    SamLars Registered Users Posts: 2
    Apprentice Traveler
    I have the same problem. Also the current speed is often not shown correctly..
  • barerun
    barerun Registered Users Posts: 18
    Apprentice Traveler
    i had such problem quite often. with almost year of experience i know it is about wawing of hands by the time of running to strong uphill - like stairs - or fast running downhill... probably at this moment the sensor is switching to the regime when counts movement. for a past time i got used to have my hands a bit under control and results are more reasonable.
  • warmup
    warmup Registered Users Posts: 1
    Apprentice Traveler
    I have been having this problem only recently since last release 1.7.53. Only difference is that I use a Spark 3 watch.
  • scubajorgen
    scubajorgen Registered Users Posts: 12
    Outstanding Explorer
    Body movement
    @barerun Thanx for the suggestion. I already wondered how the watch could discern between heart rate and body movement. In fact light is transmitted through the skin and received by a sensor. Differences in transmittance due to blood perfusion are recorded. I can imagine that when the watch moves due to body or hand movement, this can easily be recorded as 'heartrate'. In fact when you tap the sensor with your finger (watch not on your wrist of course) you can easily simulate a heart beat.
    However, when I take of the watch from my wrist and pointing the sensor into the blue it still records a heart beat. I would prefer that the watch indicates no heart beat.

    Earlier firmware behaviour
    As @Warmup suggested, the behaviour in earlier versions was different. In earlier versions (1.3.255) the heart rate was occasionally set to 0 in the TTBIN file. I checked this out on an old TTBIN file:

    External HR sensor
    I bought a Polar H7 chest strap heartbeat sensor. Works like a charm.
    To the left the recording during a 20 km run. To the right an interval in which I tried to run an interval 160-170-160 bpm. Another 160 interval at 13:36. Little peaks at 12:48, 12:55 and 13:00 correspond to running up a bridge/fly-over.
    (Apparently about every quarter of an hour one missing value if you look close enough...)

    Though the HR sensor in the watch is a nifty feature, an external HR sensor is far more reliable
  • tfarabaugh
    tfarabaugh Posts: 16,973
    There are two issues around heart rate using optical HR monitors, and these are on all devices, not just TT ones: low heart rate and HR spikes. Low HR is often seen in rowing, cycling and weight lifting. Any time you do an activity that squeezes or tenses the forearms (like the pull stroke in rowing, bearing down on your handlebars in cycling, or virtually any weight lifting move) you are squeezing the blood vessels the watch is reading, so it sees this as a reduced pulse. It is not that the watch is having a problem reading your pulse; it is that your pulse at the wrist has actually dropped because you are temporarily cutting off blood flow to the vessels it is reading. I have experienced this with every optical HR I have used, including a Mio and a Scosche unit. For these sorts of activities you are better off using a chest strap synced to the watch if getting a more exact reading is important to you. Based on numerous tests I have performed, I find that with weight training it is generally 5%-7% lower based on the wrist than the chest, so if I do not use the strap I just adjust accordingly.

    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.

    When worn properly the watch should be very accurate for most people (some physiologies will be less accurate - skin tone, arm hair, tattoos, etc. all play a factor). The watch also needs to be worn rather tight (but not to the point of uncomfortable) and needs to be worn much higher up the wrist than a regular watch (about 1" above the wrist bone). Any light seeping under the band will cause interference. You also need to let it settle down before using. When you first go to an activity screen you will notice the HR pop up, but it will be light gray. Once it has established a strong signal it will get bolder, which is an indication it is ready to go.

    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.
  • scubajorgen
    scubajorgen Registered Users Posts: 12
    Outstanding Explorer
    Thanx for the explanation. It sounds plausible and its what I expected. I found during cycling that the HR sometimes drops to 80-100 which corresponds with the cadence.
    It doesn't explain why the watch 'measures' a HR when not wearing the watch.