So you're countering my point by saying that doing certain twisting and bending movements
may help correct a specific problem? Strong argument.
I'm saying that, in general, people should be training for core stiffness and stability. This correlates with reducing movement in the lumbar, which is particularly true as you increase loads.
This is in response to people assuming that they need high amplitude concentric/eccentric contractions in their core to get hypertrophy/a 6 pack/rid of love handles etc. Most people are doing those movements to look good, and they simply don't need to. I say that they shouldn't do them because, more often than not, they will be reinforcing a dysfunctional movement pattern and doing nothing to correct core stability deficits. At worst, people will be doing damage.
When you consider that there are vastly more functional exercises for the average individual that induce the same/better strength, hypertrophy and motor pattern improvement, core training that focuses on lumbar movement is obviously significantly outmoded.
There may well be therapeutic reasons to include exercises that have movement in the lumbar spine (I've had some done to me), but they are quite obviously not relevant to this discussion and I don't know why you'd bring them up. Again, we were clearly talking about the performance and aesthetics of the average individual with regards to core training, not any spinal movement ever.
For clarity, I only said "you're not
meant to do them at all" as a tongue in cheek response to Wes saying "you're meant to do them such-and-such a way". I did not intend for it to be quite this inflammatory!
Please look into some of McGill's material, he will explain it far better than I can. I've seen lumbar tolerance to movement and load described as a sliding scale between low movement/low load to high movement/high load, with the latter being the most dangerous. McGill talks about it in terms of power, where the aim is to have low power through the spine with either low velocity (movement) or low force (load).
I can't post the material that I have, but here is some McGill action:
http://www.sportsrehabexpert.com/public/167print.cfm
http://www.t-nation.com/free_online_article/most_recent/an_interview_with_dr_stuart_mcgill_part_ii
...there is LOADS of literature to back up what I'm saying.
Also, are you saying that you're the actual the S&C coach or physio for professional or international athletes? If so, that's pretty interesting. I would also be genuinely interested in talking to these coaches and physios you reference in point 6.
I can't believe I wrote all that for this redundant argument!