Kristine Gray's interest in athletics is more than making a good shot or playing tight defense on Jefferson High School's girls basketball team.

Gray averaged 16 points and 10 rebounds a game the last three seasons. But the 17-year-old senior center, who was named to the all-Potomac District team, wanted to know if there was any physical reason why she excelled while others didn't.

So on her way to registering an unparalleled career point total (1,023 in four years on varsity), Gray spent the last two months of the 1984-85 season completing an unusual science project, using her teammates and other Jefferson athletes.

In her study, "A Comparison of Maximum Oxygen Uptake and Vertical Jump in Female Athletes," Gray evaluated the performance of athletes in two activities: the athlete performed a vertical jump for power and a muscle endurance test. Then Gray drew a correlation between the two.

As far as Gray knew, no one, student or professional, had ever done such a study.

"The project itself was a requirement for two classes, Advanced Placement Biology and Physics," she said. "I wanted it to be something I would enjoy. You see the same things at fairs year after year, like crossing two different kinds of peas. Mine had to be original."

No doubt originality had something to do with Gray's first-place award in the Biochemistry Division at her school's science fair. She also took first place at the Fairfax County Area II and III Region Science and Engineering Fair at Robinson March 31. In a letter of commendation from the U.S. Air Force, she was lauded for her "scientific curiosity."

Gray's curiosity was aroused after a brainstorming session with Lou Sharp, who is a private swim coach.

"He reads about athletics and physiology, looking for ways to improve his training techniques. He knew a lot about the kinds of things I wanted to know about athletics," said Gray, who also has competed in volleyball, soccer and track and field.

"We were talking about the project back in January and mentioned the vertical jump. That was something I knew about from basketball. I asked a lot of questions and finally stumbled on oxygen uptake, which is measured by the Harvard Step test."

She began with Sharp's library of articles on exercise physiology. He helped her weave through a maze of scientific jargon.

"I found that there are two types of muscle fibers: fast-twitch and slow-twitch," Gray said. "Each person has a fixed proportion of each. If a person has more fast-twitch fibers, he will excel in short duration events.

"I was also able to learn about the way muscles convert energy into work and whether oxygen is required for the process."

The energy system that dominates in sprinters (short bursts of energy at a high level of intensity) is anaerobic, or oxygen independent. Athletes such as football players, high jumpers and shot putters would use this system more and should perform better in the vertical jump test.

Similarly, the energy system that dominates in endurance competitors is aerobic or oxygen dependent. Marathon runners, bicyclists and distance swimmers have cardiovascular systems that are more developed and these athletes should perform better in the Harvard Step test.

"I gave background information in my display and the judges talked to me most about that," Gray said. "It really made me nervous. I wasn't sure if they understood it, so I thought they didn't like it.

"It took about a week to get the data," she said. "I mostly tested the girls on the basketball team just before or just after practice. The people in track and some of the other sports I had to catch between classes."

The vertical jump test was easy. Each athlete stood against a wall with one arm straight up. Then, with one running step, the athlete jumped as high as possible and touched the wall. Each point was recorded and the distance between the two was the test result.

The Harvard Step test for muscle endurance was harder. The subject steps up and down a bench 30 times a minute for five minutes, then the pulse is measured. The amount of oxygen used is read from a special graph, a nomogram, and depends upon how much the person weighs. "People who use a lot of oxygen predominantly slow-twitch muscles had the lowest vertical jump scores," said Gray. "And the people who used less oxygen predominantly fast-twitch muscles could jump higher. The two are inversely related."

Which means?

"Coaches can test incoming athletes and find out the activity that that person would do best in," she said. "After that, a training program can be used to develop a person's strengths and overcome limitations."

Gray also found out more about basketball players' physical makeup.

"Basketball players tend to be a mixture of the two types of muscle fibers," she said. "You would think a sport which requires you to sprint up and down the floor and to jump needs sprinters. But actually, you're on the court for so long that it takes endurance."

Gray, a member of the Virginia Vogues AAU team, hopes to take this knowledge, and her talent, to a college program. Journalism or coaching are possible careers.

"When I am on the court with four other talented players, that is the most incredible feeling in the world," she said. "It is my dream to play in college. Now I have some understanding of the physiology behind the sport."