Heart rate only accurate WHEN STOP WORKING OUT

mikeski
mikeski Registered Users Posts: 4
Apprentice Seeker
edited January 24 in TomTom Sports
When i am at the gym the watch keeps dropping out heart rate down even though i know my heart rate is up there in real time. To get an accurate reading i need to stop what i am doing and wait for it to stabilize.
I s there any way to keep an accurate heart rate throughout the whole workout?

Comments

  • tfarabaugh
    tfarabaugh Posts: 16,949
     Superuser
    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.