One of the big perils of high mileage training is birdbones- literally! As the body dumps all the fat it can it'll start to thin out, and even hollow out the bones. Yeah, this was a real medical study and everything. I remember crossing that line and how creepy I felt. It's a training adaptation, but not a good one! Weight work will reverse it.
Some people break more easily then others too- weight training will help there ('nother study... )

Lizzy

In training to go make groceries on her Ugly Bike