In reply to edsned:
As it is off road you are doing, Sarah Rowell's book, Off Road Running, is probably worth looking at.
I am a fan of Matt Fitzgerald's books, you may have seen Racing Weight mentioned on these forums, but the book I would recommend is called Run: The Mind-Body Method of Running by Feel, despite the title it is not full of mumbo jumbo and has lots of interesting stuff on how we can run better.