Physio aside, those that want to build large abdominal muscles (i.e. a six pack) try resistant training for abdominals.

Rope pull downs allow you to adjust the weight so you can crank out 8-12 reps of intense abdominal exercise.

Weighted leg ups using a dumbell are also good, especially for targeting the lower abs.

You wouldn't do 100 reps to work your chest muscles, so don't do it for abdominals either.

Chris