biomechanics of passage

The passage is a complex movement that few dressage horses attain. But why is it so hard for them to learn and so difficult for trainers to teach? And what are the effects of the passage on the horse’s body? Until recently, those questions have been difficult or impossible to answer. Thanks to modern technology, however, researchers are now able to dissect the biomechanics of the passage and unravel some of its mysteries.

“When we understand the biomechanics of dressage, it becomes easier to see why some horses have trouble learning specific movements, and it makes us better equipped to figure out exercises to train and condition appropriately,” said Hilary M. Clayton, BVMS, PhD, Dipl. ACVSMR, MRCVS, professor and McPhail Dressage Chair Emerita at Michigan State University, in East Lansing. “An understanding of biomechanics also indicates which anatomical structures are being loaded as the horse performs specific movements, which helps to predict injury risk, and this can be applied in developing conditioning and rehabilitation programs.”

Clayton and Sarah Jane Hobbs, PhD, of the University of Central Lancashire Centre for Applied Sport and Exercise Sciences, in the U.K., recently investigated biomechanical variables involved in passage. To do so, they studied the passage movements of three highly trained dressage horses as their riders took them over four force platforms. The scientists placed reflective markers on the horses and performed simultaneous motion capture analysis using 10 infrared cameras. Altogether, they explored 20 passage steps with fine technological detail.

They were able to make specific mathematical observations on how the horses use their weight, shift their balance and center of gravity, and time the movement of their legs to perform the passage, Clayton said. Their recorded data will be useful in future studies and should allow researchers to develop concrete recommendations for trainers, while also providing a basis for musculoskeletal evaluations in dressage horses, she said.

“I want to explore how dressage is performed and to delve into the intricacies of what a horse must do to achieve the highest levels of performance,” Clayton said. “Sarah Jane Hobbs, an engineer and experienced rider, and I have been working on this topic for several years. We’ve spent countless hours discussing how horses control their balance and, more specifically, how they achieve the advanced state of balance that allows them to perform difficult dressage movements in self-carriage. It’s been a fascinating journey, and we’ve learned an incredible amount along the way.”

Those in-depth scientific and practical discussions, as well as their current research, have allowed the pair “to approach dressage training from a base of knowledge that will guide the sequence of technical training and physiological conditioning so that strength and technique develop together,” Clayton said.

“For example, the need to strengthen the horse appropriately is crucial in building a successful dressage athlete,” she continued. “It doesn’t matter how talented the horse is; there are no shortcuts in the conditioning process. It takes as long as it takes, and without sufficient time, the horse will not stay sound.”

Their study identified specific kinematic and kinetic variables that affect the way a horse places himself in an uphill balance to perform the passage. Consequently, it also revealed why some horses fail to perform the passage, due to a lack in the strength or coordination necessary to achieve this posture, Clayton said.

“Dressage horses have to learn to move in a more uphill posture and to minimize trunk oscillations (swinging) during the stride,” she said. “They achieve this by adjusting muscle tension to alter the way the forelimbs and hind limbs push against the ground.”

This work could also help riders better select their future dressage mounts, to help ensure not only their capacity to do the work but also their soundness.

“If a rider hopes to compete through Grand Prix level, it’s important to choose an appropriate horse, meaning one with good balance and a strong back rather than one with enormous gaits that will be difficult to collect,” she said. “Our research has also shown that the horse’s ability to work with the hind leg engaged forward under the body is an important trait. This means we should avoid horses that have a conformation with the hind leg out behind the body, which most often results from having an over-long tibia. This is a difficult conformation for a high-level dressage horse.”

A horse’s failure to passage could be due to a lack of skill on the part of the trainer and/or the horse, as well as a lack of understanding about how the passage works, Clayton added.

“The ability to learn these difficult movements is what differentiates a top-level competitor,” she said. “We know our sport isn’t easy, but by understanding the nature of the difficulties, I hope we can help to solve some of those difficulties.”

The study, “An exploration of strategies used by dressage horses to control moments around the center of mass when performing passage,” was published in PeerJ.