Study Connects Piaffe’s Ground Force Reaction to Balance
The piaffe is an impressive, high-level dressage movement in which horses lift their diagonal pairs of legs in rhythm without forward momentum. And it’s not an easy movement: Few horses reach the level of performing piaffe, which requires considerable strength, stability, and self-carriage, according to biomechanics researchers.

To better understand the piaffe and its effects on a horse’s biomechanics, U.S. and British researchers teamed up to investigate the ground reaction forces (GRFs) of elite dressage horses performing the movement over pressure plates. Although forces varied from horse to horse—likely indicating different training techniques—and stride to stride, overall,  the researchers found horses in piaffe adjust the ground forces as needed from one step to the next to maintain their balance, said Hilary Clayton, BVMS, PhD, FRCVS, Dipl. ACVSMR, McPhail Dressage Chair Emerita at Michigan State University (MSU) and president of Sport Horse Science, in Mason, Michigan.

Specifically, horses performing piaffe kept their feet on the ground longer with lower peak vertical forces in all limbs but higher vertical impulses in the hind limbs than at a collected trot, for example, Clayton said.

“Piaffe has a more even weight distribution between the fore and hind limbs compared with the trot and, although the peak forces are not as high as in the faster moving gaits, the unusual limb positions—hind-limb joints flexed to lower the haunches, forelimb joints extended to raise the forehand—may apply different loading patterns to the joints,” said Clayton’s co-author, Sarah Jane Hobbs, PhD, of the University of Central Lancashire and director of the Centre for Applied Sport, Physical Activity and Performance, in the U.K.

“Another consideration is that each hoof is on the ground and bearing weight for much longer in piaffe than in trot, so the demands on the horse are quite different,” Hobbs said.

Studying Ground Reaction Forces in Elite Dressage Horses During Piaffe

Clayton and Hobbs used pressure plates, hidden under a rubberized runway in a large arena, to measure the GRFs of seven elite dressage horses having competed in Grand Prix events and at the Olympic Games. They also recorded visual images of the horses’ movements using high-quality video cameras and motion tracking devices for the horses’ hooves, which were each marked with retro-reflective markers.

They did this because horses generate GRFs when they press their hooves against the ground to produce locomotion. Recognizing these invisible forces is key to understanding how horses move and compensate for lameness, said Clayton.

Clayton and Hobbs then created unique GRF profiles for each of the study horses, reflecting how each horse used forces to gain and maintain balance.

The detailed results, they said, should shed light on what the horse is doing in this learned movement, and how it should be trained.

“Based on the fact that piaffe is ultimately performed without any forward movement implies that balance is an important component of the horse’s ability to be a good piaffer,” Hobbs said. “By studying the GRFs, we can learn a lot about the challenges faced by the horse in learning how to master the piaffe.”

The Biomechanics of the Piaffe: A Diagonal Movement, but Not a Trot

As a diagonal movement—meaning diagonally positioned limbs (right forelimb and left hind limb and vice versa) at the same time—the piaffe is similar to the trot and the passage, another high-level dressage movement that’s like a very slow trot with an exaggerated lifting of the limbs. However, unlike the trot and passage’s forward movement, the piaffe, which shouldn’t allow the horse to travel anywhere, never has a moment of suspension at which all hooves are off the ground, the researchers said. Because it’s both slow and static (not advancing anywhere), the piaffe requires horses to always have one set of diagonally placed feet on the ground.

“Since piaffe is performed in place, it has a greater reliance on static equilibrium than passage with adjustment of GRFs likely to play a major role in maintaining balance,” Clayton and Hobbs stated in their paper, recently published in Animals (Basel).

“Knowledge of forces is the most basic component of understanding gaits and movements and has practical value for trainers in developing better strategies for training and strengthening dressage horses,” said Hobbs.

Understanding the Forces of Piaffe From a Veterinary Point of View

In addition to training benefits, the biomechanics findings of the piaffe have critical health and veterinary implications, the researchers stated. “Our study can help veterinarians in understanding why specific injuries are associated with certain levels of training,” Hobbs said.

The results can also give insight about managing dressage horses “so that they can stay fit and sound while moving up the levels of competition,” she said.

“Beyond the basic scientific interest in piaffe itself, forces are ultimately responsible for the development of most lameness issues,” Clayton explained. “So knowledge of how limb loading in piaffe differs from the trot and passage will help us to understand the etiology of certain injuries and suggest ways to prevent them.”

Clearly, the piaffe has unique challenges, the researchers said. “The study showed without any doubt that different horses learn to perform piaffe in different ways that could reflect differences in conformation or strength of the horses or different training techniques—for example, whether horses learn to piaffe from the walk or trot,” said Clayton.

“In the trot, horses generate very consistent GRFs from stride to stride, whereas in piaffe the GRFs, especially the longitudinal and transverse forces, are very variable from one stride to the next,” Clayton continued. “This reflects the fact that the horse is struggling to stay balanced with only two limbs on the ground.”

The study, “Ground Reaction Forces of Dressage Horses Performing the Piaffe,” was published Feb. 8, 2021, by Animals.