I like the anatomy-trains site, but whereas it works on tension and compression as primary quantities and shear as secondary, I tend to think in shear terms as the non-decomposed primary quantity, because it preserves the necessity to see the rotations occuring in all axes.
A very interesting site worth going through and understanding on the placement of fulcrums (fulcra?) and relative mechanical advantage gained by USING the shear in a mechanism, vice trying to compensate it away (the way we do in "normal" muscular joint leverage) is found here: http://www.spinalfitness.com/
I noted the same thing about shear related to the AT site. Thanks for the link; I'll check it out.