Here's a book that stresses functional training and has some good core exercises:
Author:
DiNubile, Nicholas A.
Title:
Framework : your 7-step program for healthy muscles, bones, and joints
Publisher: [Emmaus, PA] : Rodale, c2005.
DiNubile's main exercises for the back are (as I recall):
- Pillar stretch
- neck roll
- pretzel twist
- ab crunches
- cat
- plank
- superman
In my experience,
planks are the quickest for developing overall core strength and endurance (back
and ab muscles). You get in a pushup position, but with your elbows on the floor. You hold your whole body straight and rigid for as long as you can. Time yourself, and add time every time you do it. This is HARD, but it strengthens you up FAST.
And it hurts so good!