That's really interesting...
After my 40mi ride (not a lot for a lot of ladies, but about 2x what I usually do) I was a little sore, and after some 'encouragement' (okay, not that much) There was 'naughtiness' and my gf freaked that I was 'spotting' about a week before I was supposed to get my period. I ended up not bleeding for 3 days after that, then having horrific cramps the first and second days of my period. (Sorry if TMI, but such is the nature of this thread I suppose... )

I'm wondering if all the strenuous activity had anything to do with the earlyish bleeding and then cramping?

hmm...