Heart rate monitor not right

craigev8
craigev8 Registered Users Posts: 1
New Traveler
edited January 24 in TomTom Sports
whats going on with my heart rate monitor
it starts of ok then it has a fit and its all over the place
it can be 67 then 99 but it never goes over 110
then it will jump up to 145 for thirty seconds then go back down to the
67 - 99 range
its really throwing my training out as i cant get a accurate reading
iv tried all tricks swapped wrists cleaned my arm before using put it on the inside of my wrist
iv got a feeling that there is less lights than there used to be on the sensor

any help ?

Comments

  • tfarabaugh
    tfarabaugh Posts: 16,935
    Superuser
    There is a single light on the sensor as there has always been. You do not state what activities you are engaging in, but there are many sports for which a wrist based HR sensor is not your best option. There are two issues around heart rate using optical HR monitors, and these are on all devices, not just TT ones: low (or variable) heart rate and HR spikes. Low or variable 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.
  • wmterhaar
    wmterhaar Registered Users Posts: 3
    Apprentice Seeker
    tfarabaugh wrote:
    Low or variable 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.

    This seems a decent explanation, but there is something I don't understand. I get seemingly very accurate heart rate values when I do weight training on machines, but when I take part in a Bodypump or GRIT lesson, I have the same problems craigv8 describes, and not only with the parts of the lesson with weights, but also with excercises like burpees.
  • tfarabaugh
    tfarabaugh Posts: 16,935
    Superuser
    wmterhaar wrote:
    This seems a decent explanation, but there is something I don't understand. I get seemingly very accurate heart rate values when I do weight training on machines, but when I take part in a Bodypump or GRIT lesson, I have the same problems craigv8 describes, and not only with the parts of the lesson with weights, but also with excercises like burpees.
    It just has to do with the specific motion and movement involved. In my experience weight machines seem to be smoother with less clenching than using dumbbells. You will get it with burpees because every time you drop down for the push up you are tensing your forearms. Best to stick with a chest strap for anything involving weights, push-ups or the like.