"An important charateristic of this(the back) mechanism is that this spinal rigidity increases proportionately to the speed. Further, spiral rigidity is the means by which the epaxial musculature converts hind leg energy into speed."
Jean Luc Cornille

Over-rhythm/speed creates rigidity in the spine.

This is how the body naturally protects the spine. Protecting the back. Speed is the anti-thesis to the relaxation we seek and the full mobility of the back and the loin that is the hallmark of the correctly trained dressage horse.

By Nadja King