06/06/2001 11:00PM

Stride goes a long way determining stamina

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LEXINGTON, Ky. - All too often people refer to speed or stamina as if they were static quantities, like the hardness of granite. In truth, however, these qualities are more changeable, like intelligence, and are owed to a number of factors working together, such as inheritance, environment, health, and training.

Researchers into the movements and inner workings of racehorses realize how all these effects work together. Jeff Seder, president of EQB, a firm that evaluates horses' hearts and strides, said that the interplay of the different elements "is like a symphony. There are a lot of ways for the notes to come together and work." When they do, there is a symmetry and balance in the natural systems that produce the harmony of speed.

In the Thoroughbred horse, these factors influence the degree that a horse can show speed or stamina. Although many things contribute to stamina, "the most important thing is an efficient stride," according to Dr. Paul Mostert, a noted researcher into the mechanics of racehorses.

A professor emeritus at the University of Kansas and owner of the Mostert Group research organization, Mostert is the principal investigator on a new research grant from the National Science Foundation that was announced last month. So, like Seder, he knows a thing or two about how horses propel themselves round racecourses with speed and grace.

Mostert defines stamina as "the ability to cover the most distance in the shortest time and with the least effort." That sounds fairly simple once you think about it, but not all horses run the same way.

Mostert said that "some horses will be very efficient at one speed but not at another" because of the way they are built or because of the way other systems, such as the heart and lungs, help or hinder a horse in reaching its potential.

"The number-one user of energy," Seder said, "is the number of strides per second, or stride frequency. So you're better off using an efficient stride, if you want to cover a distance of ground. But the interesting thing is the very best horses can do both. They can switch styles from the quicker stride to the more efficient one. The lesser horses are mostly stuck doing one thing. And you can see this when you analyze slow-motion photography of the horses working."

In assessing the motion of a horse, Mostert mentioned a classic-placed horse from the past decade that "had as efficient a stride as would be possible to have but also had the smallest heart I've ever seen in a distance horse. His heart size was well below average, but he was still able to go a distance of ground because he could get into that effortless stride."

Clearly, a very efficient stride allows a horse to overcome a lot of different things. As an example of another type of horse, Mostert mentioned Unbridled's Song as "one of the most athletic horses I've ever been around because of the quality of his physique, muscle tone, and desire to win. These allowed him to go far beyond his efficiency. He had a nice, long stride but used too much action to get there."

Both of these horses, although very talented racers, had to overcome some inefficiencies to show their best "because a lot of things go into stamina and making a good racehorse," Mostert said. "A strength in one area takes up for a weakness in another, but the horse with all the elements is a supreme champion."

Another horse with a very efficient stride was Thunder Gulch, the sire of two runners in the Belmont Stakes, Point Given and Invisible Ink. Mostert noted that "Thunder Gulch had a good, efficient stride, although it wasn't as good as John Henry's, but he had this wonderful heart, and he could pump all this oxygen through his system to keep that long stride going throughout his stretch runs."

Thunder Gulch is not a very tall horse, nor was Northern Dancer. Yet both stayed 10 furlongs really well, winning the Kentucky Derby, and Thunder Gulch won the Belmont also.

Intuitively, most people expect small horses to be at a disadvantage against larger horses, but Mostert said, "As a general rule, stayers need a long stride for their size, and although Northern Dancer would not have a stride like a Point Given, he wouldn't necessarily be far off it, and it takes a surprising amount of energy to move a really big horse." So, under some conditions, a smaller horse might actually have an advantage.

Also, the types of strides that sprinters and stayers use are different. Seder noted that the strides "vary by the energy they use and the speed they provide. Not surprisingly, you use more energy in going very fast." Visually, some observers can distinguish some differences between types of horses by looking at them.

For example, sprinters tend to have a quicker, shorter stride, and to do their job most effectively - reach the highest speed possible - they need a lot of muscle power. They are the massive, bulked-up power lifters of horse racing. Not only do the specialist sprinters tend to look different, with their wide bodies layered with mounds of muscle, but many are actually constructed differently also.

"They are utilizing power over efficiency," Mostert said. To get the most power, the sprinter has to have big levers in his hindquarters, and to move them quickly, he must have big muscles. This big, blocky look is the most common profile among sprinters.

American horses rarely race farther than 10 furlongs on dirt and are notable for a combination of muscle, balance, and efficiency that has become the American type for the classic distances.