[BerntR]

I watched their DVD's a couple weeks back, Bernt, and they mention it in their 2nd and 4th DVD. They mention a lot of things in those DVD's so it is very possible to miss their remarks imo.
ICT

Martin said he had studied biokinetics so I assume it was more than a mention on a couple of DVD's. But there are not so many ways to rotate your shoulders and still have roughly the same geometrical forward bend, so he might as well has piced this up from somewhere else.

In any case: Kelvin has written several papers that deals with how the spine works in the golf stroke in an entirely different and more detailed manner than I've seen anywhere else. Sidebend in the down stroke is an important part of it. And a TGM flat shoulder back turn / steep shoulder down turn is very very very close to what Kelvin has found when he has studied some of the best current golfers. What I see in S&T in this regard is very different and not as well founded, IMO. But that is based on the H2 pictures in the book, since it is not very well described.