a tweet from Bora caught my eye and sent tme to (
which in turn sent me to the YouTube videos. From there I found this April 18, 2008 summary at the Jurga Report
FEI STATEMENT ON HYPERFLEXION (ROLLKÜR): the following statement was adopted: There are no known clinical side effects specifically arising from the use of hyperflexion, however there are serious concerns for a horse's well-being if the technique is not practiced correctly. The FEI condemns hyperflexion in any equestrian sport as an example of mental abuse. The FEI states that it does not support the practice.
Rollkur was first brought to the public's attention by a German dressage magazine that was highly critical of Dutch dressage rider Anky van Grunsven's warmup routine before her Grand Prix performance. (The article was published in 2004) The criticism led to disputes between many factions of the dressage community. Researchers including America's Dr. Hilary Clayton and France's Dr. Jean-Marie Denoix presented evidence to the FEI at a special forum on the subject last year (in 2007) Veterinary researchers could find no evidence of direct harm to the neck or spine of the horse.
In late 2007, a new book called Tug of War: Classical Versus "Modern" Dressage: Why Classical Training Works and How Incorrect Riding Negatively Affects Horses' Health by German veterinarian Gerd Heuschmann became a manifesto for condemnation of the practice
Background on the controversy: Dresseur Pervers (2005)