So I want to figure out this test fixture as described here:
Next, we applied a three-point bending load on each panel
with our MTS machine. The machine exerted loads parallel
to the grain on the cedar samples, and parallel to the
face grain on the plywood panels

I read that to say that they had the machine force on the edge of the panel, with the panel supported on two points, i.e. a triangle (3-point bending load) with the machine being the top of the traingle, and two base points holding the sample. The panel in my vision is standing on edge, not laying flat, because they say "The machine exerted loads parallel to the grain on the cedar samples, and parallel to the face grain on the plywood samples." Parallel to the grain- would that not be pressing on the edge? To me pressing on the face of the layup would be perpindicular to the grain. Am I right here?

The MTS machine in this picture looks pretty much as one would expect - sample supported at ends, force applied in the middle.
http://www.westsystem.com/ss/assets/galleries/Testing-large-bonded-in-fasteners-GalleryPage/_resampled/ResizedImage389273-05fasteners.jpg

I understood the grain orientation explanation to mean that the sample grain (plywood face or strip) ran 'across the machine' from support to support... i.e. testing long-grain stiffness vs cross-grain. Panels 'flat' in the test jig.

I agree it is not very clear- an illustration would have helped.

On the main topic: I guess I'm not very 'in tune' with my boats when paddling, as I never sense any lack of hull stiffness in my commercial glass boats or S&G or strip boats..... ;-)
Perhaps this is more of an issue when trying to build very light panels to make a 20# boat???
I certainly recall watching the hull of a v. light Kevlar solo canoe flex in moderate waves.