Effect of temperature on (measured) heart rate

[raven89]

Now that it's getting warmer where I live, fitbit tells me my heart rate during exercise is much higher than usual. As in, a full 20 to 30 bpm higher consistently, even though workout intensity is very similar to what I usually do. My resting heart rate on the other hand isn't going up.

Is fitbit mis-measuring or does it actually make sense for my heart rate during exercise (ónly during exercise) to be that much higher when it's warm? I do know that temperature generally correlates to heart rate but 30bpm difference over a slight temperature change seems excessive. I thought it could also be related to blood vessels expanding the hotter it gets, but idk

[t.parker]

@raven89 I experienced significantly elevated HR during holiday in the Philippines when I was running with weather temperature of 35°-40°C (on some days more). However, the more I was exposing myself to heat the better heat acclimation worked and eventually HR started decreasing for the same level of effort. I used chest strap so the accuracy was spot on (I don't trust wrist sensors). I did one local 5k race there and that was probably my slowest 5k 🤣 yet HR reached 191bpm. After coming back to England to temperature around 10°C at the time, there was quite a drop (gradually ovet a few days) in my HR during runs. Interesting experience.