Small sidenote. MBE showed that sit ups, only strengthen the Rectus Abdominis (the famous 8 pack) and actually can make backpain worse. A good core workout on the other had trains your deeper muscles (which are type I, so slow contracting muscle tissue) for endurance and trains your full core.
Sit ups triple the pressure put on the Disci Intervertebrali in normal circumstances and can lead to a hernia.
Als sit ups train the muscle to have lots of Type II muscle tissue. Which doesn't stabilize your core as the muscle gets tired very quickly due to depleting Creatine and ATP supplies in your muscle.
Type I on the other hand uses Krebscycli (aerobic energy) to work. So they can work alot longer.
and Kembudo, as a physician, you should know that a good core is required to do the exercices you mention. Yes they build muscle of the top layer (Musculus Lathisimus Dorsi and to some extent the musc. Spina Erector). Again, these are type II muscles and cannot perform the role of stabilizer.
The small deep muscles on the other hand CAN do that. As they are type I.
These are the muscles that need to be trained for a solid core:
http://catalog.nucleusinc.com/generateexhibit.php?ID=9299
If someone wants more information. I'll be happy to reply
(p.s.: I don't want to be a smart***, but there are alot of misconceptions about the lowerback/hip/sacroiliacal area out there. Most of the advice given, has been proven to actualy worsen it. Prevention is the key. And since I'm so close to the source, I would like to share this info with people who can benefit from it. I'm a fysio therapist student by the way.)
It comes down to core training. Again and again. Also running helps to develop these muscles.