As discussion over the effects of riding horses’ head and neck positions continues, Dutch scientists have determined that all non-natural head and neck positions, including those similar to the modern-day competitive dressage position, affect breathing, and hyperflexion ("rollkur") causes the greatest effect.

Artificial positions–head and neck positions created through tack, pressure, and training–cause a "dynamic obstruction" of the airways, making it more difficult for horses to inhale, said Inge Wijnberg, DVM, PhD, assistant professor of equine internal medicine at the Faculty of Veterinary Medicine at Utrecht University, in the Netherlands.

Like a cricked garden hose, the trachea (or windpipe) probably becomes kinked in these artificial positions. Meanwhile, surrounding tissues, especially the neck muscles, might push and bulge into the trachea causing further constriction. The result is the same as with the cricked garden hose: increased pressure and reduced flow.

"This phenomenon would (also) explain the abnormal inspiratory (inhaling) respiratory sounds sometimes noticed when an extreme position … (is) assumed," Wijnberg said.

To test this theory Wijnberg and colleagues investigated the effects of five different head and neck positions–including hyperflexion–on seven healthy Dutch Warmblood horses trained to a basic dressage level. Handlers longed the horses at the walk, trot, and canter, with fixed reins holding their heads in the required position for testing. The researchers tested each horse in every position and g