What is the rollkur controversy in dressage?

Rollkur — also known as hyperflexion or low, deep, and round — is a training technique in which the horse's neck is flexed so severely that the nose is pulled toward the chest, placing the horse's face well behind the vertical in an extreme position that proponents argue develops suppleness and strength while critics argue causes physical harm, prevents genuine throughness, and contradicts the foundational principles of classical dressage. The controversy became one of the most heated debates in contemporary equestrian sport after video footage of prominent international dressage trainers using rollkur in warm-up arenas became widely available, revealing that a technique most dressage practitioners were unaware of or had considered marginal was in fact being used by some of the sport's most successful competitors. Critics from the classical tradition — including Dr. Hilary Clayton, Andrew McLean, and numerous classical trainers — argued that the extreme behind-the-vertical position of rollkur prevents the horse from being genuinely through, compresses the larynx and trachea restricting breathing, creates muscle tension in the neck and back that is the opposite of the suppleness the technique claims to develop, and may cause permanent damage to the cervical vertebrae and associated structures. Defenders argued that rollkur was a temporary training position used briefly as a stretching and suppling exercise rather than a sustained working frame, and that experienced trainers applied it with horse welfare in mind. The FEI's response — distinguishing between rollkur as a sustained training practice, which it prohibited, and low, deep, and round as a briefly used exercise — attempted to navigate the controversy without fully endorsing either position, and the continuing debate over where the line falls between acceptable deep work and prohibited rollkur has remained unresolved in competition.