Inaccurate heart rate readings?

geoffreymiles Registered Users Posts: 1
New Traveler
edited January 24 in TomTom Sports
Hi, over the past few weeks I've noticed that increasingly often my spark 3 reads abnormal heart rates for the exercise I'm doing. I'll be biking at roughly 24-28kph, which usually gives me a heart rate of 140-180 and if I look on my spark 3 it reads 90-100.
If I check my own heart rate with the stopwatch I come to numbers way higher.

If I rest for a few seconds, my heart rate starts climbing up. Is this because of the temperature of my arm? It's about 4°C/39°F outside at the moment, I'm wearing a jacket and gloves.


  • tfarabaugh
    tfarabaugh Posts: 16,948
    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. You are leaning on your forearms, compressing the blood vessels and reducing blood flow. When you stop to rest you are letting up and the vessels are opening and the pulse goes back up. 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.

    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.