High-speed video gait analysis has potential for identifying elite equine athletes early in training

by Kenneth L. Marcella, D.V.M.

ON A CLEAR June day in 1878 in Palo Alto, California, Eadweard Muybridge set up 12 cameras with electronically controlled shutters. Abe Edgerton, a trotter, was harnessed to a sulky and driven past the cameras, which took 12 photos in about one-half of a second. In this brief moment, Muybridge proved a point: He showed that during a horse's running stride, a moment of suspension exists when no hooves touch the ground.

That same moment also was the beginning of the field of high-speed gait analysis, which has evolved into kinesiology, or the study of the forces that cause movement (kinetics). Today, high-tech cameras used for gait analysis record more than 250 frames per second, researchers are breaking down the complex motion of the exercising horse, and massive data banks are helping to define equine motion in ways that previously were unthinkable. Unthinkable, because they were not even visible.

The human eye cannot distinguish events occurring in less than one-tenth of a second. Even seasoned horsemen watching a workout at the track end up missing a good deal of that horse's motion, and what they usually come away with is an impression of the horse's way of going. They may "see" something they like about a particular horse, or not like the way another horse moves. Knowledgeable horsemen have the experience to form more accurate impressions (often called "developing an eye"), but a wealth of information still is being missed.

Motion of the horse

Kevin Keegan, D.V.M., M.S., a veterinary researcher in the E. Paige Laurie Endowed Program in Equine Lameness at the University of Missouri at Columbia, is taking gait analysis one step further. He feels that what we previously thought we saw in a horse's gait sometimes may not be what actually was happening.

Keegan, along with other veterinarians, recently presented a series of papers at the 51st annual American Association of Equine Practitioners convention in Seattle. These lectures were an in-depth look at the motion of the horse, focusing on some of the simplest clues that all horsemen use when evaluating an unsound horse--the head bob for forelimb lameness and the hip hike for hind-limb lameness.

Keegan began with the age-old standard description of lame foreleg motion, quoting from the textbook Adam's Lameness in Horses: "As a result of lameness in a forelimb, the head will drop when the sound foot lands and rise when weight is placed on the unsound foot or limb."

"This is, indeed, what actually happens in severe forelimb lameness and, because of the limited temporal resolution of the human eye, what appears to happen to the naked eye," Keegan said. But a horse, even at a slow trot, moves at four meters per second, and these head-bob explanations are simplified, incomplete, and sometimes misleading. "The adage 'down on sound' is not always correct," cautioned Keegan, who further explained that there are many different head-motion patterns for various degrees and locations of forelimb lameness. Some types of lameness confirm what was previously thought about head and neck motion. Some lamenesses produce motion that goes against current ideas.

Similar concerns exist for the use of the hip hike as an accurate marker for hind-limb lameness. Use of high-speed cameras and gait analysis allow Keegan and others to break down the motion of sound and lame horses and then to correlate the site of the problem with differing gait patterns. This process generates a massive amount of data that is used for research, monitoring of a particular horse's rehabilitation program, and an aid in teaching veterinary students to evaluate the motion of a horse.

"In the not-too-distant future, we may be able to produce a means of high-speed video analysis that would then be able to localize the lame leg and the site or location of the lameness within that leg," Keegan said.

Not all equine kinetics researchers feel this lameness-gait-analysis concept is right around the corner, but they all agree, as expressed by Hilary Clayton, B.V.Sc., Ph.D., chair of the McPhail Equine Performance Center at Michigan State University, "We are all at a really exciting point."

Clayton pioneered gait analysis for equine rehabilitation and sports medicine use, and she currently is applying this technology to lameness evaluation and performance critique. Eight cameras in Clayton's laboratory allow for a real-time video of a horse's motion.

"What used to take one week of filming to analyze can now be done in hours," Clayton said. The technology is available, the database is available, and the most difficult part of the analysis is knowing what parameters to test for.

Researchers look at:

•Stride length;

•Stride frequency;

•Velocity;

•Joint angles;

•Vertical movement of the croup and withers;

•Relative position of limbs at each phase of the stride; and

•Timing and placement of the hooves.

Elite versus non-elite athletes

Many variables must be considered when trying to unravel the riddle of equine motion, but elite horses can be shown as moving "better" or more correctly than non-elite horses, and the search to harness this predictive ability of gait analysis has been going on for years.

On the performance side of the gait-analysis question, Clayton has been looking into what makes an elite equine dressage horse or jumper unique. She noted that at the dressage competition in the 1988 Seoul Olympics, the highest marks were given to horses with the longest, fastest strides at extension. Gold medalist dressage horse Rembrandt had a stride length of more than 16 feet compared with 12 feet for the majority of the other competitors.

Clayton found that winning Olympic jumpers had briefer times between their forelimb impact and the initiation of the next stride. Essentially, these horses were able to move more quickly than other horses, yielding faster times. Fewer penalties were received by horses whose hind legs were placed closer to each other prior to taking off for a jump and whose forelegs landed nearer each other, as well.

Elite Thoroughbreds

Analysis of the extreme racing gait of an elite Thoroughbred is perhaps the area where the information provided by high-speed kinetics most seems to throw open a door to the previously unseen and unknown.

Jeff Seder of EQB Agents and Consultants in West Grove, Pennsylvania, began with a business and filmmaking background. He applied what he knew to getting good film of racehorses. He also began collecting data on elite equine athletes by attending Thoroughbred sales.

"Prior databases [mostly academic] included average athletes, and the information did not exist to describe the elite horse," Seder said. "So we became obsessive-compulsive about getting good data." Experts like Clayton agree.

"Mr. Seder has amassed a wealth of data and has been generous in providing that information for study," she said. Seder has published much of his data in a series of articles that evaluates the various detailed phases of gait in racing Thoroughbreds. Perhaps more controversially, he also wrote an article that relates racing performance to foreleg flight patterns among 900 unraced two-year-olds offered at major sales in the United States. Seder listed a group of 73 horses with "good" motion and a group of 77 horses with "bad" motion. The latter group showed extraneous foreleg motion, including hyper-rotation of the cannon bone (hoof hitting an elbow in extreme cases); winging, paddling, or wobbling; and other deviations from straight and correct motion.

"Good" movers were patterned more closely after the ideal. All horses compared were matched to have workouts of similar velocity.

The subsequent North American racing performances of these two groups were evaluated. Seder concluded what proponents of high-speed gait analysis had hoped for when the technology first began to be used. He wrote: "Extraneous foreleg motion was shown to be related to subsequent racing earnings and the level of competition attained. Horses with good foreleg motion (as defined and determined with high-speed film evaluation) earned more and had greater stakes-level success (83% higher earnings) than horses with bad foreleg motion."

Seder's data also has yielded information about high-leg-action horses and turf racing, about the lack of performance predictability when trying to use only velocity and length- of-stride measurements, and several other very technical facts about the vast differences and arrays of phases contained within the racing gait of the horse.

Seder pointed out that The Green Monkey, a Forestry colt recently purchased for $16-million at the Fasig-Tipton Calder sale of selected two-year-olds in training, had a fabulous 9.8-second workout, but high-speed film revealed that the entire work was done at a rotary gallop, a very quick gait that can produce fast times but costs more energy. In Seder's opinion, such a gait is unlikely to be maintained for longer distances. High-speed analysis of that horse's motion leaves questions in Seder's mind and puts tremendous, maybe excessive, expectations on the horse. "Really good horses have a number of ways to run fast," Seder said. "And if they are 'correct' in their motion, they will be able to generate more power and speed without tiring out or breaking down."

Seder did not set out to ruin the careers of those horses that were deemed to have bad motion in his study, and in a bit of kill-the-messenger mentality, he said he has sometimes not been well received within the racing industry.

"Roughly 80% of horses bred for the track will have some sort of problem and never make it to an elite status," Seder said. "The history of science is that innovation is met with skepticism. I'm just taking science and playing probabilities, looking for those horses that, based on our data of gait and motion analysis, have a higher chance of making it."

Whether you use the latest in cameras, high-speed analysis, and data evaluation, or you hang near the rail to find a way of going that pleases your eye, everyone is looking for the same thing--a horse that has a good chance to make it.

Kenneth L. Marcella, D.V.M., is a practicing veterinarian in Canton, Georgia.