Tends to be 40-43 in the mornings (I take it 3 times a week)... as others have said, if I've got a cold starting it goes up above 50 and stays there until the virus passes - a good indicator of being ready to go back to running is when the low reading comes back. I would suggest that rather than looking at the readings themselves, it is more important that they are consistent and changes above 10 bpm are when you should have any concern.