Compression can appear in a truss, for example, despite no compressive forces. 17000 N of compression equal a 1.73 ton weight (3820 lb) on your back, and you sitting perfectly straight for it to be only compressive, and not cause shear etc..
Yes, it does create shear (altough not in "my model"- overly simplistic and maybe completely wrong, but the only I could think of that could so amplify the load).
Well, if the spine is "perfectly straight" (as in "normal curvature), wouldn't the compression actually force the nucleus in every direction?
(although since the vertebrae aren't perfectly horizontal, the nucleus will be squeezed more in one direction).
But the "if you flex it is squeezed backward/forward" is cool. Since the disk is non-contractile, simply bending should apply a lot of stress to it (Hooke's law), in order to strengthen the connective tissue (make it adapt),right? (applying the SAID principle, allowing recovery etc. -basically, considering ideal conditions are given).
There are doctors not agreeing with dr. McGill, and Nick Tuminello also noticed that a dead pig spine* flexed to tissue failure is NOT a the spine of a living human, which also regenerates and adapts. BTW, wouldn't this -flexing-extending a dead spine- be equal to having a dead biceps, and loading while passing an electric current through it to simulate concentric and eccentric action, and after many cycles say that exercise will lead to a biceps tear?)
*"First off, upright flexion is not normal pig function. The only time a pig stands upright (on two legs) is when itâ??s trying to hump another pig.
Secondly, pigs donâ??t have any functional movement similarities to humans what so ever. This goes back to what Comerford said above."
If I got anything wrong, please oh please correct me. No, I'm not joking.