You don't often find scientists staging arm-wrestling tournaments - let alone competing in them. But then the match scheduled Monday at the International Society for Optical Engineering conference in San Diego is no ordinary bout.

For the first time, researchers plan to pit man-made muscle against living tissue - in this case the sinewy limb of a San Diego high-school senior. The purpose of this unusual test of strength: to spur scientific interest in a little-known but promising class of plastics that expand and contract when jolted by an electrical charge.

Officially known as electroactive polymers, the material is more frequently referred to by its nickname - artificial muscle.

Long regarded as a laboratory curiosity, the material has begun attracting more serious attention in recent years. Researchers are now incorporating it in plans for everything from toys and robots to implants and prosthetics. Some scientists envision a day when the material might replace the real muscle in people whose own fibers have failed.

"The properties of artificial muscle are getting much closer to that of biological muscle," says Selahattin Ozcelik, a robotics researcher at Texas A&M University.

Theoretically, Ozcelik says, artificial muscle can be used in place of any mechanical motor and offers several key advantages. Lighter than a traditional motor, artificial muscle can unleash quick bursts of stored energy. As a plastic, it's also capable of bending and twisting.

Financed by a small grant from the Office of Naval Research, Ozcelik and his colleagues have designed a snakelike robot composed entirely of braided artificial muscle fibers. By electrically stimulating the fibers in the right sequence, Ozcelik says, the robot could slither into tight spaces or over rough terrain in ways that a mechanical robot would find hard to match.

For this reason, NASA and the Defense Department are keenly interested in the technology and fund several projects to meld robotics and artificial muscles.

For example, a team at SRI International, a nonprofit research institute in Menlo Park, Calif., is working on a government project to build a robot capable of hopping over obstacles. In 1998, the institute created one of the first walking robots with artificial muscles, dubbed "Flex."

Still, says SRI's Roy Kornbluh, "the very first applications of artificial muscle might be more mundane."

Last year, the institute spun off a company called Artificial Muscle Inc. to pursue some of these applications. One example of a more prosaic home for artificial muscles: your car's automatic door locks.

But researchers at the new company have also developed a flat speaker out of an artificial muscle membrane. The prototype has the fidelity of "a small boom box," says Kornbluh, possibly making it ideal for automobile headrests and other locations where conventional, cone-shaped speakers won't fit.

Other scientists are considering artificial muscles for medical applications.

At the University of California, Irvine, biomedical engineer William Tang and one of his students have just launched a project to develop a prosthetic hand with artificial muscles. Unlike mechanized models now in use, a plastic-powered prosthetic could be more deft and ultimately stronger, says Tang.

"We could also potentially make the motion more lifelike," he adds.

Implants are also in the works. Mohsen Shahinpoor, director of the Artificial Muscle Research Institute at the University of New Mexico, has designed an adjustable eye implant to correct bad vision.

The fix, he says, involves wrapping a small band of artificial muscle around the eyeball. Stitched to the sclera, the eye's protective white outer layer, the material would tighten or slacken in response to a hearing aid-like electromagnet clipped behind the ear.

As the band squeezes and relaxes, it changes the shape of the eyeball and thus alters the distance between the lens and the light-sensitive retina at the back of the eye. This determines whether images appear fuzzy or crisp.

"You push a button behind your ear to focus on images that you see with your eye," explains Shahinpoor, who has launched a small company called Ophthalmotronics Corp. to develop the technology.

So far, he says, the idea has only been tested in animals and cadavers. He's hoping to get approval from the Food and Drug Administration to conduct further tests.

Artificial muscle technology may also be a boon for toy makers. A small Japanese firm called Eamex Corp. has introduced the first artificial fish tank. The colorful, eerily lifelike fish swimming inside contain no mechanical parts or batteries. Instead, the artificial muscles in their tails swish in response to an electric signal beamed by a hidden antenna in the aquarium.

Despite recent progress, scientists stress that considerable technical hurdles remain. Among them: boosting the strength of artificial muscles while simultaneously reducing the electrical power they require.

That's where the arm-wrestling comes in.

The contest was first proposed in 1999 by Yoseph Bar-Cohen, an artificial muscle researcher at NASA's Jet Propulsion Laboratory in Pasadena, Calif., who wanted to encourage researchers to tackle these problems.

Bar-Cohen says three teams have entered Monday's competition: one from the Swiss Federal Institute of Technology, another from the University of New Mexico, and team of undergraduate underdogs from Virginia Tech.

"We have no experience with electroactive polymers," says Steven Deso, an engineering science major at Virginia Tech. "We're just trying to go to the competition with something that can move."

Representing humanity in this man-vs.-machine matchup is 17-year-old Panna Felsen. "I'm not very strong," she says, "so chances are they're going to beat me."

Bar-Cohen says he chose Felsen because the La Costa Canyon High School senior is a straight-A student and an amateur robot builder who has been accepted to Massachusetts Institute of Technology.

But he admits the fact that Felsen is a girl may have also been on his mind. As one of the field's pioneers, Bar-Cohen wants to give artificial muscles a fighting chance.

Still, the NASA scientist jokes that he isn't taking chances with the 5-foot-7-inch, 120-pound former competitive swimmer.

"I told her not to practice," he says.

To see demonstrations of artificial muscle technology, visit http://ndeaa.jpl.nasa.gov/nasa-nde/lommas/eap