What happens when the horse bends in the flexible middle section? For one, this motion by some considered anatomically impossible, is not the vertebra's elegant lateral curve, called Längsbiegung, which is effect by the setting of the poll. In the so called Rippenbiegung the ribs under the rider's leg move closer together on one side and further apart on the other, causing an ever so slight lateral movement in the vertebrae T9-12. These very vertebrae have a horizontal flexibility, which is much larger and evident for instance in jumping. They are the self same vertebrae in which the modern horse's warp originates.
In a straight horse the haunches do the majority of work and adjustment in locomotion. The torso, closed in from behind, remains straight, calm and in raised position. The lower neck participates in the movement's direction. The rider steers and directs the horse using the self same provisions of the upper neck and head, which the horse uses to manage itself. This type of horse needs no bending in the ribs. It mobilizes in the haunches easily and willingly fulfills the rider's wishes. It is the horse in Längsbiegung, which d.l.G. refers to.
The warped horse, however, may benefit from bending in the ribs. Increased lateral elasticity furthers the transfer of the backbone's mounting from the sacral joint all the way to the withers to obtain a calm and composed torso. It by the same token addresses the flexible middle section's warp.
There is a distinct difference in impulsion though. The straight horse on the haunches has mobilized. The horse whose warp is addressed in Rippenbiegung tends to slow down. Bending in the ribs, as well as overbending the upper neck and the croup are restrictive means to maintain control over the powerful modern horse.
