Making Sense Of Movement

You could gather a mountain of measurements and calculate and chart different variables on your computer to your heart's content, but the trick is to sift out the information that is relevant to your application. What can motion analysis tell you ?

In humans, biomechanics has found successful application in several areas. In orthopedic medicine and rehabilitation, a injury's mending progress can be monitored; in manufacturing or business settings, methods to enhance efficiency of certain job tasks can be found; and in sports medicine, motion analysis has been used to improve athletic performance in a variety of sports, including golf, track and field, baseball and tennis. Motion analysis has even aided in the development of a space suit for NASA.

Studies of gait analysis in horses with high-speed cameras figures were first published by researchers in the 1970's. Building on this foundation, other researchers have described the gaits of Standardbred trotters and pacers, galloping Quarter Horses and Thoroughbreds, dressage horses, jumpers and cutting horses. Once normal equine gaits were described, exceptions on both sides of the spectrum could be distinguished.

At one end are horses whose gaits deviate from the norm because they are lame. In these cases, gait analysis plays a diagnostic role. To check for soundness or hoof balance, horses are usually filmed at the trot since this gait is inherently symmetrical and any signs of lameness (i.e., any disruption of symmetry) are exaggerated at this pace compared to the walk. For example, suppose you taped a sound horse moving at a leisurely trot, then viewed the tape in slow motion. You may be surprised to see that the diagonal limb pairs do not strike the ground simultaneously, as it is commonly thought they do. Instead, the hind limb often precedes the fore both at hoof impact and lift-off. But in a horse who is lame, the sequence and timing of limb placements and lift-offs may differ or: the right and left sides.

Horses undergoing rehabilitation may also benefit from gait analysis. Just as physical therapists could use biomechanical analysis to evaluate a patient's progress, a clinician could compare a horse's movement before and after treatment to help evaluate its effectiveness.

At the other end of the gait spectrum are talented horses who perform in a superior manner. Their ability to move more economically or efficiently than their less gifted peers contributes to their success in competition. When a superstar comes along only too rarely, the contrast can be spectacular, as in the classic of Secretariate.

Clayton and Deuel each have focused research in this area, and because the skills to excel at one equestrian sport may differ significantly from another, they've found plenty of work to do.

Clayton's statistical analysis of cutting horses videotaped working a flag, including experienced performers of both average and superior proficiency, showed that each horse's ability could be correctly classified by looking at two variables: run distance (defined as the maximum distance between the center of the flag and the horse's nose during the trial, i.e., how far the horse lagged behind the flag during the course of his run) and which body part moved first as the horse initiated a turn formers had an average run distance of 218 centimeters (87.2 inches), while the superior horses averaged only 147 centimeters (58.8 inches), indicating that they kept up with the flag better. Mediocre performers moved their forelegs first when turning in a vast majority of the cases, while top-notch horses used their heads and shoulders more frequently. By moving these upper body parts first, a horse can shift his center of gravity to one side, so that the thrust of his limbs is directed at a sharper angle, and he gains greater maneuverability.

Studying Seoul dressage competitors, Deuel discovered that stride characteristics at the extended trot and canter were quite consistent with overall scores. Highest marks went to horses who had the longest, fastest strides and displayed the greatest degree of extension. Goldmedalist Rembrandt clearly gave an outstanding performance: his stride length at the extended trot measured a full 16 feet, compared to "only" about 12 feet for the other horses. Deuel also noted that winning jumpers at the 1988 Olympics differed in their recovery strides after negotiating a fence compared to their competitors. Successful horses had briefer time intervals between hind limb impacts and briefer time intervals between fore leading limb contact with the ground and the initiation of the next stride. Fewer penalties were garnered by horses whose hind limbs were planted closer together during take off and whose forelimbs landed nearer each other.

There are still some questions to answer before gait analysis can be used routinely to pick the youngsters that will go on to become stakes winners, futurity stars or Olympic contenders, and weed out early those that are structurally disadvantaged or poorly coordinated. It is generally accepted that an individual's inherited movement patterns can be enhanced by practice (your piano teacher didn't say "Practice makes perfect" a million times for nothing - those drills induced subtle refinements in your neuromuscular coordination to translate notes on a page to accurate movements of your fingers).

However, researchers are just now scratching the surface to understand how much equine gait characteristics change over time due to training and/or maturity, and which characteristics are reliable predictors of ability in a given sport. To complicate matters, the final performance is more than just the sum of the horse's innate talent and any improvements through training. It involves the ability of the rider or trainer, the nature of the working surface, farriery modifications, the overall health of the horse and that elusive, unquantifiable quality, "heart."

Nevertheless, as both a performance predictor and diagnostic aid, gait analysis holds great promise. Whether you want to compare limb to limb, before to after, your horse to a superstar, your horse to a composite "ideal" or your horse to the norm, its advantages are clear: gait analysis is

• noninvasive (no wires or sensors attached to the subject; skin markers optional),
• flexible (cameras are portable and can be set up just about anywhere, from the clinical setting to the competition arena),
• quantifiable (you can change your question from "is this horse lame?" to "How lame is this horse?") and
• permanent (a film or tape can be replayed again and again, forming a baseline for comparison or part of an archive; the stored data can be analyzed and presented in innumerable ways to give a ras clearer picture of what is happening).

In addition, the technology is now more accessible than ever.

Meanwhile, as the winners in Barcelona take home their medals, Clayton and Deuel will be returning with bundles of tapes just as precious. Olympic fervor will die down, but the world-class performances of the equine athletes who gave it all in pursuit of the gold will be relived in the university laboratories as the process of analysis begins.