Resting heart rate and your cycle

I know this is not strictly relating to swaying, but as there is a wealth of knowledge on here when it comes to TTC in general, I thought I might get a great opportunity to learn something from you all!

Basically I know most ladies on here will be tracking their ovulatory cycles by monitoring their BBT as the main indicator. But when I was looking at the resting heart rate data from my fitbit (which mostly just sits there on my wrist every day) I saw this:

Attachment 37322

“Hmm!” I thought. It goes up over a few days. Then it comes down again. Only by a small amount, but still. It’s very neat, I can’t think of any outside factors as to why this would be occurring other than it being linked to my monthly cycles.

Unfortunately this is where my own research ends! Due to my BC I don’t have AF and I have not been monitoring my cycle with BBT or any other way, so I don’t actually know how they tie together. I did a little googling on the subject and found some stuff (including a FANTASTIC graph one lady on reddit had produced showing her RHR against her O/AF). I came across a bracelet which claims to monitor your fertility by taking heart rate into account which was pretty interesting. But in general, it doesn’t appear to have the same following as monitoring BBT.

So I wondered if any of you folks have any more info on this? Perhaps other ladies with fitness trackers who also track BBT could enlighten me as to how closely they link?
Is there any viability to using resting heart rate as a method to track your cycle? If not, why not? I know the readings from fitness trackers need to be taken with a pinch a salt when it comes to reliability!

This is all mainly just in the interest of science for me :) I do love data and seeing how it all ties up, but I am wary of monitoring too many of my own stats because this boy-mum tendency is already by far the biggest obstacle in my pink sway haha!

Thanks in advance for any input! Hopefully someone other than me finds this interesting :)