I've been using a Fitbit to track my resting heartrate (among other things). The value has consistently been in the 55-60 range for several weeks (most typical value over the past week or two is 57). Over the past few days, however, it jumped to around 62; a 10% increase.
The bulk of the increase occurred 2 days ago, and the only thing I can think of that happened within that timeframe is that I got a mild sunburn (from kiteboarding, so primarily on my face/forehead from looking up at the sky all afternoon). But correlation doesn't necessarily mean causation. So my question is, can a sunburn lead to an increase in the body's resting heartrate? And if so, why?
I know a Fitbit isn't a medically accurate device, and that there's pending litigation over whether they're accurate at all. However my anecdotal experience with my particular device is that it's quite accurate when at rest (during strenuous exercise the instantaneous readings can indeed be a bit funky and it can temporarily lose count altogether; although the average values that get logged to the dashboard seem reasonable despite the transient outliers/glitches). So I don't think device inaccuracy/margin of error is the explanation.