April 2019 - Biomechanical Brilliance: Dr. Hilary Clayton
Written by article & photos by Kim F. Miller
Friday, 29 March 2019 01:49
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dressage

Technology facilitates advanced understanding of how high-level movement happens and traits likely to be found in a successful dressage athlete.

article & photos by Kim F. Miller

Dr. Hilary Clayton’s biomechanical perspective on the dressage training scale was a Health Fair highlight during the California Dressage Society’s annual meeting in Southern California this past January. “I’ve been trying to make it out to the CDS meeting for many years and I’m glad I finally could,” said the renowned veterinarian and equine biomechanics expert. Attendees were even happier about her appearance.

The demands of basic and high-level movements and the conformation and gait characteristics that enable the horse to execute them provided a fascinating context in which to think about training development and techniques.

The use of “force plates” at Dr. Clayton’s unique sporthorse performance lab at Michigan State University was instrumental in analyzing gaits far beyond what the human eye can see. Embedded under a special runway, the force plates quantify how the hoof pushes against the ground to generate movement.

Infrared light reflectors placed on joints and other parts of the horse’s body send signals back to a computer. The collected data is translated into  real-time stick figures that depict precise details of how and when each body part moves, and how it relates to movement elsewhere in the body.

Such sophisticated tools are needed to fulfill Dr. Clayton’s goal of measuring “gaits, performance and movements of the modern-day dressage horse.” The goal is to update, rather than replace, “the good information from the old masters,” she emphasized. The ongoing research and findings are relevant for the ever-improving quality of today’s horses, as well as today’s higher quality riding and competition standards.

Most importantly, “We want to determine what qualities in a horse can help or hinder it becoming a good athlete,” she stated. “And what are the qualities that won’t stand up to the training needed to make a top athlete.”

Correlating the findings to the Dressage Training Scale, Dr. Clayton began at its base: rhythm, which she defined as “regularity and tempo,” and with an emphasis on the diagonal gait, the trot.

Diagonal Coordination

The first issue she addressed was purity of the gaits and how this should be evaluated. Measuring diagonal coordination was the first point of focus. “Are the footfalls of the diagonal pairs (i.e, left hind, right front) occurring at the same time?” she asked as attendees studied two still pictures. One showed dramatic front leg extension: the other, less dramatic extension and the hoof lower to the ground. She drew attention to how the diagonal limbs swing forward in relation to each other and whether the footfalls of the diagonal hooves are synchronous.

In a more trained, typically older horse, the hind hoof usually hits the ground first. This is also the typical footfall sequence in the modern dressage horses bred for naturally uphill conformation and movement, she noted. “Modern horses are bred with uphill conformation and dressage training enhances that.”

Studying the degree of limb rotation was the next step in this phase of gait analysis. “How is the leg protracting and retracting relative to the horse’s body?

Is there a big change in the angle of the leg between maximum protraction and retraction?” The ideal is that the leg is fairly vertical at the time of impact, as the horse’s body begins to roll forward over the front leg. “You want the horse to be able to push up and off before that leg gets too far under the body. A more vertical forelimb supports the withers in a higher position.”

As the degree of collection increases, the range of motion between protracting and retracting decreases. Elevated trotting in place, piaffe, for example, requires a combination of the haunches sinking down to carry and the foreleg pushing upward to elevate the forehand. “Maximum elevation of the forehand is possible when the foreleg is vertical,” she explained.

Looking for parallel diagonal limb movement came next. “Compare the hind cannon bone to the front leg forearm, because the lower front leg is swung forward from the elbow,” she explained. Here’s where the major fault of slowness in the hind end can be detected. She showed examples and made comparisons between horses that were too slow with the hind leg versus horses that had a good hind leg with excessive elevation of the foreleg. “I often hear people say that they want a more expressive front leg, but I want a really quick hind end,” said Dr. Clayton, who studies dressage from the ground and the saddle.

Dr. Clayton described this research as being in fact-finding, not answer providing, mode, as far as what gait characteristics are most important. “My own question is which element -- synchronous footfalls or synchronous swing of the fore and hind limbs -- is a better indicator of purity of gait?”

More research is planned to elicit those answers. Meantime, she’d made some conclusions: “Hind hoof first disassociation of the limbs is desirable, in my opinion, because it indicates that the horse is working in an uphill posture and is in self-carriage. And it may be that parallelism and synchrony of the forward swing of the fore and hind limbs is a more useful indicator of gait purity in trot than the synchronicity of diagonal hoof contacts with the ground.”

Dr. Clayton explained why core strengthening is critical to performance and health in the dressage horse.

Suppleness

Dr. Clayton defined this next rung on the training scale as “elasticity and freedom from anxiety” and as having both physical and physiological components.

She noted that movement in the horse’s spine is what many mistakenly consider critical for suppleness. “What’s important from the horse’s standpoint is the ability to control and stabilize the spine,” she clarified. That puts a premium on strengthening the muscles that stabilize the horse’s back.

“A horse’s back is like a beam supported by the front and hind legs. That beam is pulled down from below by the horse’s guts, which weigh several hundred pounds, and is pushed down from above by the weight of the rider.” Those forces result in the maximum sag of the spine right where the rider sits, between the T12 & T16 vertebrae.

“It’s not surprising that this is where we see kissing spines, in which the tips of the spinal processes on adjacent vertebrae contact each other and rub together,” she explained. Poor performance and general stiffness are common symptoms, along with, to a lesser extent, persistent bucking and poor hind limb action. Conversely, she noted that Xrays may reveal contact between spinous processes in horses that show no clinical signs.

At the trot, the rounding and hollowing of the back that occurs during each stride is caused by forces associated with the gait, not by muscular contractions that flex and extend the joints between the vertebrae. Importantly, back movements are controlled by those muscles. Hence, core strengthening is critical to a horses’ ability to attain and maintain its back in a rounded outline that facilitates suppleness and good health.

She recommends pre-ride carrot stretches to wake up, stretch and strengthen the many tiny muscles that stabilize the spine. With the horse at a standstill, use a carrot, treat or other target to move the horse’s head sideways toward the shoulder, flank and hock, to tuck toward its chest and to reach toward the ground. In the beginning, have the horse standing square on stable ground. When the horse is fully experienced in doing the exercises, the degree of difficulty can be increased by doing the exercises on a vibrating floor plate or with the horse standing on an unstable surface such as Surefoot® pads.

Lunging and riding in resistance bands such as the Equicore system also helps to activate the core muscles that stabilize the back. Jumping even small grids and fences builds core strength, too.

 

 

Stronger back muscles also help the horse elevate its forehand. Dr. Clayton illustrated this with a slow-motion video of a foal lifting its forehand off the ground, while rising up from grazing on its knees. She pointed out how its back muscles helped with that effort.

Dr. Clayton, right, with one of many CDS attendees thrilled by her presentation on how biomechanics apply at each level of the Dressage Training Scale.

Tilted Turning

“Left to their own devices, a horse trotting around a circle of 6 meters diameter will lean inward by 15-degrees, which facilitates generating the centripetal forces needed to turn the body,” she explained. “We want dressage horses to turn with their legs vertical to the ground while developing the turning force using the abductor and adductor muscles.”

These muscles should be developed gradually starting on large circles and teaching the horse to work on progressively smaller circles as strength improves.

Spiraling in on circles of gradually smaller sizes will help develop strength in the muscles, such as the pectorals, that enable the horse to follow a curved track without the inward lean. However, turning with the limbs vertical to the ground is not natural, and it puts different forces on the musculoskeletal tissues. That’s another reason to make progress slowly when developing a horse’s skills in turning and circling.

The horse’s inability to have equal lateral bending through the length of its spine was illustrated from an overhead view of the spine. “Transition regions” of the spine are located at the poll, the base of the neck and around the T16 vertebrae. These are where most of the bending actually occurs. “Seen from the top down, there is very little bending at the joints between those points,” Dr. Clayton explained. Applied to a shoulder-in or haunches-in, the rider should understand that most of the bending motion is occurring right under where they’re sitting, along with the horse displacing its front feet or its rear end relative to the middle.

Power Points

Addressing impulsion, Dr. Clayton noted that a horse’s physical ability to go forward elastically is dictated to a large extent by recoil of the elastic tendons in its lower leg that are stretched when the fetlock extends as the leg bears weight. These tendons are strengthened by exercise early in the horse’s life. Adaptation is complete by the time the horse is two years old.

Young horses that grow up in a natural environment with room to run and play over uneven terrain typically have much stronger elastic tendons than those raised in relative confinement. Knowing how a young prospect grew up is an important detail for assessing its long-term suitability for dressage.

The elasticity of these tendons also makes them more vulnerable to repetitive strain injuries. Varying the type and intensity of exercise, and the terrain on which it’s performed, are good preventative measures. So is including easy or rest days in conditioning programs and the use of post-ride lower leg icing after strenuous workouts to reduce inflammation.

Attendees appreciated Dr. Clayton’s clear and enthusiastic way of presenting her research and left with heads full of new knowledge to apply in their riding and training.