Clare,

As part of your ab workout, make sure you target the transversus abdominus muscle - it's a postural abdominal muscle and can't be exercised by simply doing sit-ups and crunches. It's THE most important ab muscle and is the one muscle you should strengthen if you have any kind of back problem.

It can take several weeks to condition the muscle though, so you have to persevere.

Here are a few sites that might help (including exercises to strengthen):

http://www.spine-health.com/topics/c...xercise02.html

http://www.bodybuilding.com/fun/ms-fit5.htm

The second link is from a bodybuilding site, but gives a good example of how to exercise the muscle.

And don't let the course profile faze you - you never know what you're capable of until you try.