I noticed the claim that Rollkur was not more harmful for the horse's breathing than the vertical head carriage. Well, yes, when the horse's face is vertical the breathing is compromised, with the possible exception of the pure Arab wide between the jowls with the mitbah (thin and fine where the neck meets the jowl bones) and free, big wind pipe. Drinkers of the wind. However even Arabs prefer to have the nose out front a little so they can breath better.
This is why the flexion should be at the poll with the poll highest. Then the face is NOT vertical or BTV and the horse can get enough air into its lungs for the hard physical activity they are required to do. Of course if the horse has to go FAST he pokes his nose out even further so more air can get into the lungs.
AND the horses are supposed to be IN FRONT OF THE vertical, not at the vertical. That only recently in the rules has been changed to include at the vertical in piaffe (which imho is a BIG mistake as well).
If you look at Rheiner Klimke's riding, his horses were never behind the vertical. Then again, he didn't get as high of marks as we're seeing these days and the horses are of a different type. However, common sense seems to indicate that rolkur looks very unnatural and kind of grotesque.
There ARE many studies (look for them on googlescholar.com). And the high marks of today are a joke imho. The training of a horse out of balance DOES affect the purity of gaits....we can ignore that and only want the submissive aspect.
Klimke was one of the greatest dressage trainers and has a huge impact on the way I train my horses and ride others. Look at his daughter. Her cross country rides are almost perfect. Her dressage is beautiful. Reiner said in one his books that to keep his horses happy and always learning, he cross trains them. His high level dressage horses would also go to a few jumper shows and vice versa. Any equine sport that is judged has a sense of corruption to it. No matter what sport, there are always going to be the "cheaters" who are abusing the system. I teach my horse to work with her conformation and her natural stride and in turn we both have happier, better rides. If I don't get high marks on my tests, I don't care. I have seen too many 4 star rides get these amazing scores with very ugly tests in my opinion. I figure if my training style took my horse, who was abused and trusted no one and was called a "rogue" horse, and turned her into the loving, sweet mare she is today, then I must be doing something right.