Anky didn't create it, Francios Baucher did around the year of 1850. But Anky and the top riders have modified it, after what I've learnt. The original thought is to keep it for 1-2 seconds to stretch the horse and get it's full attention..I think, I havn't read the whole book yet:P I'm not really sure what I think of it if it's used like that. Maybe I could tolerate it on some horses... I'm not sure.
But as the top riders ride today..it's just disgusting. It's against all what dressage stands for; the horse is on the shoulders, nose far behind the vertical, the aids are all but subtle.. and that's not even mentioning the moral issues and how the horse feel. I'd cramp in my neck if it was held like that more than a minute..
Only thing it does is that the horse keeps the nose in place and thus you eliminate the most obvious sign of inbalance; that the horse throws up the head o regain balance. Even when the horse is allowed in a normal head position, it's still on the withers since it hasn't learnt to carry with the hindquarter.
I ride classical, or I'm trying to learn. My instructor has learnt academic riding (for Bent Branderup, the re-inventor of this type of classical dressage) and I've also been at his stables and had a few lessons for one of his students. She (my instructor) mostly rides centered riding tho, and has been teached from riders in the spanish riding school as well, she mixes it to a good portion of classical dressage, avoiding the overbending in academic and so on.
I'm still as much of a newbie as you can be xD But I've learnt more this few months than I have in 12 years of regular riding :P
I'm very much looking forward to a clinic with Desmond Obrien this spring, this time I'll ride for him too. (Rider in the spanish riding school in Vienna several years ago).
This drifted a bit off topic, but you did mention classical dressage. X) I can reccomend it.
I can also recomend the book ''tug of war'' if you're interested about classical vs modern dressage (fit for the competitions, which I guess mine isn't since it's a bit different yet). The website mentioned before is very good too.