Avoiding shoulder injury during high brace
As to the question of whether the ACA is teaching extended arm bracing
"anymore," I direct your attention to page 49 of Laurie Gullion's
_Canoeing and Kayaking Instruction Manual_. I know you have a copy of it.
There is a picture of a kayaker doing an elbows-tucked-in "low high
brace." That book was published by the ACA in 1987. That's, um, almost 20
years ago, which suggests that extended arm bracing was never recommended.
Perhaps there is evidence to the contrary, but I can't find it.
At least for kayaking, I'm not certain when the recommendations changed.
When I took a surf zone class a goodly many years ago (certainly more than
10), they taught the low hand position for the high brace. I recall them
mentioning "shoulder injuries," but not exactly what injuries those might
be. As for sea kayaking, when I took it up, anyway, it seemed many the
instructors were ex-WW instructors, though I could be wrong on that.
It is also possible that due to the influence of Hutchenson and other
European's (who really were the focus of sea kayaking instruction), that the
instruction/philosophy of early instructors was strongly influenced by the
BCU (British Canoe Union) and their recommendations about the sport. Whether
those included the low hand position is something requiring research.