Over the past two decades, the work of Hilary Clayton, BVMS, PhD, has elevated equine sports medicine to a whole new level. As the first incumbent of the Mary Anne McPhail Chair at Michigan State University, Clayton brings an element of modern science to the ancient art of horsemanship. Her revolutionary research is generating valuable information and a greater understanding about the ways in which horses and riders move and interact.

Established in 1997, the concept for the Mary Anne McPhail Chair for Equine Sports Medicine arose from the frustrations of the chair's namesake and benefactor after her horse developed a lameness that was never successfully diagnosed or treated. "Searching for an answer made me realize that we need more research to solve these kinds of dilemmas," says McPhail, an accomplished equestrian and graduate of Michigan State University. "Hopefully, through this research, we can begin to understand why injuries occur and develop methods of prevention."

When McPhail first met Clayton at a U.S. Dressage Federation seminar, she knew she had found the right person to perform the research that would transform her idea into a reality. Clayton, a seasoned veterinarian, researcher, rider, and trainer, brings a one-of-a-kind blend of knowledge, experience, and enthusiasm to the study of equine biomechanics, a science that she not only practices, but essentially pioneered.

Clayton now conducts her research at the Mary Anne McPhail Equine Performance Center in East Lansing, Mich. The 18,000-square-foot facility houses an indoor riding arena and a state-of-the-art data collection area. The uniqueness of the facility--and its faculty--make the McPhail Equine Performance Center a premier center for diagnosing and treating performance problems in sport horses. According to Clayton, "We are very fortunate to have equipment and facilities that are on the cutting edge. Our laboratory is the only one of its kind in the world."

Gait Analysis

To better understand the biomechanics of equine locomotion in sound and lame horses, Clayton uses a technique known as gait analysis, which, she explains, essentially measures all the things that we see--or don't see--when a horse moves. The technology converts subjective observations into comprehensive scientific analyses.

Clayton performs equine gait analysis using an automated system marketed by Motion Analysis Corporation. The California-based company is the world's largest manufacturer of video- and computer-based instrumentation systems designed to test and measure the movement of objects and animals. Currently, the technology is widely used to create animated characters in movies and video games.

"It's the exact same system that was used to produce Gollum in Lord of the Rings," Clayton notes.

The motion analysis system at the McPhail Equine Performance Center includes a computer and eight infrared cameras, allowing researchers to place four cameras on each side of the horse to be studied. "This lets us analyze both sides of the horse's body at the same time," Clayton explains.

In preparation for motion analysis, reflective markers are secured with Super Glue to the inside and outside of each horse's legs, and to the head, neck, and torso. Super Glue, Clayton jokes, is an essential part of virtually every experiment that is conducted at the center.

Horses are first recorded while standing still, allowing the computer to construct a representative stick figure based on the placement of the reflective markers. As the horse moves forward, the cameras automatically locate and track the reflective markers, while the computer generates a three-dimensional image of the horse in motion.

"This enables us to look at the horse from either side, or from any angle, including the top of the horse," Clayton says. "We can rotate the image and look at any view we want."

The computer-generated 3-D image is proving to be an important diagnostic tool in the evaluation of lame horses. While visual assessment of lameness is based on the recognition of asymmetries in the horse's stride, computerized gait analysis allows researchers to identify subtle changes before they become visible. "We can pick up changes that are indicative of lameness as soon as they occur, and actually measure and quantify specific gait abnormalities. A horse with spavin, for example, brings the affected leg in underneath itself," Clayton notes. "You can't see this when you're observing the horse from a side view, but you can see it very well when watching the horse from behind. The computer-generated figures are useful for teaching students what to look for in a lame horse since we can replay the motion repeatedly and look at it from different perspectives, without having to ask a lame horse to trot repeatedly. We can also use gait analysis to monitor the horse's response to various lameness treatments."

In sound horses, gait analysis allows researchers to better understand the mechanics of normal equine locomotion. By analyzing various aspects of the gaits, Clayton is able to determine the exact movements of the limb segments, including where and when each joint flexes or extends. "In sound horses, we can look at the differences between the collected and the extended trot," she says. "And we can see the differences in movement of horses that show good collection versus poor collection."

Although the science of gait analysis is still evolving, it is providing a wealth of useful information to riders and trainers. "We can gather data on a sound horse at the beginning of its career, and perform gait analysis at regular intervals," Clayton says. "We can see how the muscles that are used in self-carriage change from baseline (beginning values) as the horse advances through its training."

The Force Plate

To enhance the value of the information provided by computerized gait analysis, Clayton has embedded a two-foot by four-foot force plate in a rubberized runway in the center. "When the horse treads upon the force plate," Clayton explains, "we can measure the force with which the hoof pushes against the ground, and the force with which the ground pushes back against the hoof. These forces are what move the horse forward."

Data collected from the force plate allow researchers to quantify a horse's weight distribution and determine how that distribution shifts between the horse's limbs as it moves at the walk, trot, and canter, or during certain dressage movements. When data collected from the motion analysis system and the force plate are combined, Clayton can make determinations about the functions of the horse's body in motion.

"We can use this information to calculate biomechanical values that cannot be measured directly," she says. "We can measure the torque around each of the joints and determine which muscle groups are acting across those joints at different times in the stride. This information allows us to understand whether the joints are absorbing concussion or generating propulsion."

The calculation of these biomechanical values led to Clayton's discovery that the muscles around the horse's elbow are primarily responsible for swinging the forelimb forward and backward. "Previously," Clayton notes, "the shoulder joint was considered to be more important, and the knee joint was largely ignored. Now we know that the muscles of the shoulder are used primarily for stability and for attachment of the front limb to the torso, rather than to swing the forelimb forward."

Rider Analysis

One of the newest areas of research at the McPhail Equine Performance Center is rider analysis. "We can put the same kind of reflective markers on the rider's body," Clayton explains, "and use the motion analysis system to analyze the rider's movements. This helps us understand the immediate effects of the rider's movements on the horse."

The ultimate goal of this project is to develop techniques for analyzing and recording nonverbal communications between riders and their horses. Toward this end, Clayton designed a unique system for measuring rein tension during riding. Strain gauges embedded in the reins measure rein tension and transmit the information to a computer. Because the system is wireless, rein tension data can be continuously collected and recorded as the horse and rider move freely about the arena during a training session.

"Rein tension wasn't anything like I imagined it would be," Clayton notes. "I thought there would be a steady, continuous tension between the rider's hands and the bit, but we found that constant tension isn't present. It's more a series of spikes, representing the horse nodding into the reins."

Clayton says this phenomenon doesn't just occur in inexperienced riders, as might be suspected, but is present in all top riders. "It's a natural feature of the contact between the horse's mouth and the rider's hand," she says.

Another surprise came when Clayton and her team converted rein tension to units of weight. Once thought to be a matter of only a few ounces, Clayton discovered that the weight on the reins was much heavier than previously imagined. "For most horses and riders, the peak of rein tension spikes around five pounds at the trot," she says. "When you're holding the reins in your hands while you're riding, it doesn't feel like you're lugging around a five pound bag of potatoes--it's not the same. When you ride a lot, you get strong in a number of ways that you aren't even aware of."

While strain gauges measure rein tension, electromyography (EMG) is used to measure activity in the muscles of the rider's arms, shoulders, and torso. The EMG detects electrical activity in the muscles, which indicates when the rider's muscles contract or relax.

Graphs representing rein tension and EMG data are projected on the wall of the riding arena to give the rider feedback about how much tension is on the reins, along with a graphic representation of the electrical activity occurring in the muscles of each arm. This information gives the rider immediate visual feedback that goes beyond the information that can be provided by a human onlooker.

"When you ride around the arena, you can easily see how much tension is in each hand, and you can make immediate adjustments," Clayton says. "Riders very quickly get the feel for it--they learn what it feels like to have three pounds in their hands, or five pounds."

Saddle Fit

In the works is another study, sponsored by Red Shield Equestrian, that will allow Clayton and her team to measure saddle fit and the ways in which shifts in the rider's weight affect the horse through the saddle.

"With our new system, there aren't any wires connecting the horse to the computer, as there were in the past," she says. "We'll be able to see how the rider's center of gravity moves in relation to the horse's back, and with the aid of the EMG equipment, understand which muscles in the rider's seat and legs are responsible for support."

Because the technology is wireless, Clayton will be able to measure the rider's muscle activity not only at a standstill, but also when the horse trots and canters. "We can tell when the rider is sitting too far to the left, for example, or when he is gripping too tightly with his thigh muscles," she says.

She hopes this technology will eventually be used as a valuable teaching tool for riders. Watching a giant, four-sided screen hanging in the center of the arena, riders can see at a glance how their body positions and use of aids influence the movements of their mounts. The instant feedback provided by this technology will allow them to more quickly acquire skills and a certain "feel" that might otherwise take years to develop.

"A lot of top riders do certain things naturally and intrinsically," says Clayton. "Riders in the next tier can learn to do these things if we can explain to them exactly what to do and when to do it. We can help these riders advance their riding skills."

Farriery Study

As part of her ongoing research in the field of equine biomechanics, Clayton is conducting a study of the effects of a specific type of hoof trim in conjunction with Robert Bowker, VMD, PhD, director of the Equine Foot Laboratory at Michigan State University. This study is supported by the Bernice Barbour Foundation. According to Clayton, "The hoof is important in locomotion since it acts as the interface between the horse and the ground. Over the past few years, some new ideas have evolved as to how the hooves should be trimmed."

Bowker's research involves the structure and function of the hoof. He has observed that in wild horses, sole thickness is about twice that of domesticated horses. Also, the heel and frog of the wild horse's foot make full contact with the ground, allowing these structures to act as part of the support apparatus and to provide the horse with information about the nature of the ground's surface. Having identified these traits, Bowker developed a unique farriery method called the "physiological trim," which mimics the natural patterns of weight-bearing that occur in the hooves of wild horses. The physiological trim permits the tissues of the foot to optimally dissipate the shock of ground impact, so that less energy is transmitted to the bones of the feet and legs.

For the farriery study at the McPhail Equine Performance Center, Clayton kept a group of unshod riding horses on pasture during the University's summer break without trimming their feet. "This gave us a lot of foot to work with, to trim down the way we wanted," Clayton notes.

At the end of the four-month period, the horses were brought back to the barn for farriery work. "We took Dr. Bowker's physiological trim and applied it to these horses," Clayton explains. "We leveled the hoof by trimming to the live sole, then beveled off the front of the toe to facilitate break-over, and lowered the heel so that the heel and frog made good contact with the ground. We wanted to stimulate the frog to grow, because a big, thick frog provides better support for the coffin bone."

The horses involved in the study are ridden five days a week as part of a University riding lesson program. Clayton and her team take photos, perform foot X rays, and conduct gait analysis on each horse before and after maintaining the physiological trim for four months. These tests allow the researchers to determine the relationship between external changes in the hooves and internal structures of the foot.

"We look at how the outside shape of the foot is changing, and we determine how this affects the bones of the foot and the mechanics of locomotion," says Clayton. "Horses' feet have been trimmed a certain way for quite a lot of years, but there is limited information describing the effects of different trimming methods on the function of the foot during locomotion. That's what we're doing in this study--we're looking at the effects of different trimming methods on hoof mechanics."

Future Projects

One of Clayton's current projects involves the development of exercises for horses that will allow them to develop the specific muscles needed to perform dressage movements. Non-specific exercise is less beneficial, Clayton notes, as it tends to build irrelevant muscle mass, which can end up acting as a handicap. The weight and bulk of additional muscle tissue increase energy expenditure, add load to the limbs, and hinder heat dissipation during exercise.

Dressage horses being prepared for competition at more advanced levels need to build strength and endurance in the muscles that are active during collection. To maximize the beneficial effects, these exercises should train the appropriate muscles and mimic the range and speed of joint motion that occurs during the dressage movements.

"Currently," she says, "the only way to develop these muscles is to perform the dressage movements." As a result, Clayton says, "There's really no good way to prepare the horse for these movements in advance, and this makes the entire training process much slower. We need to find alternative ways to strengthen these muscles, so that horses will be better prepared to perform those movements. This will allow the horse to safely progress through the training program a little faster."

Then and Now

As a pioneer in the science of equine biomechanics, Clayton has seen enormous progress in the past two decades. "When I started doing this kind of work in the early '80s," she says, "it was very slow and tedious. Without modern computers, everything had to be done manually."

New technology makes movement analysis of horses and riders much easier, requiring a fraction of the time and effort that it once did. "Even five years ago," Clayton says, "we couldn't dream of doing the things we're doing now. It's amazing what we're able to accomplish in this super-computerized age. And over the next five years, I think we'll see phenomenal advances in the field of equine biomechanics."

Both Clayton and McPhail believe that the work being done at the McPhail Equine Performance Center will ultimately have a variety of positive, practical implications for riders and their mounts.

"It is my hope that the knowledge gained through the research conducted at the McPhail Equine Performance Center will benefit a broad spectrum of horse enthusiasts who love and enjoy their horses, and who want to give their horses the best care possible," says McPhail.

"Research is done at different levels," Clayton explains. "We're doing the big science here, using sophisticated technology that allows us to calculate data that cannot be gained by observation. Our research is very heavily based on engineering, and what we're doing represents the cutting edge of science. These scientific studies are laying the groundwork that will enable us to go on and do more practical studies. Once we get through this phase, we can apply what we learn to real live situations."

Clayton's future goals are lofty, but certainly attainable. "We want to learn more about how horses function in an athletic capacity," she says. "We want to build stronger equine athletes that are less likely to break down, and to maximize every horse's genetic potential. We want to understand and improve the ways in which riders communicate with their horses.

"Riding will always be an art, and we can't hope to replace the art of it," Clayton emphasizes. "But science will allow us to ride our horses better, and keep them healthier while we're at it."

Donations Accepted

Continuation of the research program at the McPhail Center is dependent upon donations. For information about making a tax-deductible contribution, please contact the MSU College of Veterinary Medicine Development Office, A-133 East Fee Hall, East Lansing, MI 48824 (517/353-4937). Checks directed toward the research program should be payable to MSU McPhail Research and sent to the Development Office. Gifts by credit card, stock, real estate, and bequest are also welcome.

About the Author

Rallie McAllister, MD

Rallie McAllister, MD, grew up on a horse farm in Tennessee, and has raised and trained horses all of her life. She now lives in Lexington, Ky., on a horse farm with her husband and three sons. In addition to her practice of emergency and corporate medicine, she is a syndicated columnist (Your Health by Dr. Rallie McAllister), and the author of four health-realted books, including Riding For Life, published by Eclipse Press and available at www.ExclusivelyEquine.com or by calling 800/582-5604.

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