Hi Chuck,
It's not so much a matter of keeping the back muscles strong, but the actual discs are at the front of the spine so it's a very easy access through the stomach area. You would have an extremely vicious and difficult approach trying to go through lower ribs in some cases to get to the discs at all.
If you look at an anatomical diagram you will see what I mean. Strangely enough the stomach muscles do support the back, and play a big part in your spine strength.
Best:
Alastair
