Robo-legs: new prosthetic limbs are providing increased mobility for many amputees--and blurring the line between humans and machines.

With his blond hair, buff torso, and megawatt smile, Cameron Clapp is in many ways the quintessential California teenager. There are, however, a few things that set him apart: For starters, this former skater boy is now making his way through life on a pair of shiny, state-of-the-art robotic legs.

"I make it look easy," he says.

Clapp, 19, lost both his legs above the knee and his right arm just short of his shoulder after getting hit by a train almost five years ago near his home in Grover Beach, Calif. Following years of rehabilitation and a series of prosthetics, each more technologically advanced than the last, he has become part of a new generation of people who are embracing breakthrough technologies as a means of overcoming their own bodies' limitations.

"I do have a lot of motivation and self-esteem," Clapp says, "but I might look at myself differently if technology was not on my side."

The technology he's referring to is the C-Leg. Introduced by Otto Bock HealthCare, a German company that makes advanced prosthetics, the C-Leg combines computer technology with hydraulics. Sensors monitor how the leg is being placed on terrain and microprocessors guide the limb's hydraulic system, enabling it to simulate a natural step. It literally does the walking for the walker. The technology, however, is not cheap; a single C-Leg can cost more than $40,000.

The C-Leg is one of the examples of how blazing advancements, including tiny programmable microprocessors, lightweight composite materials, and keener sensors, are restoring remarkable degrees of mobility to amputees, says William Hanson, president of Liberating Technologies Inc., a Massachusetts company that specializes in developing and distributing advanced prosthetic arms and hands.

THREE SETS OF LEGS

For example, Clapp, who remains very involved in athletics despite his condition, has three different sets of specialized prosthetic legs: one for walking, one for running, and one for swimming. In June, he put all of them to use at the Endeavor Games in Edmond, Okla.--an annual sporting event for athletes with disabilities--where he competed in events like the 200-meter dash and the 50-yard freestyle swim.

MAN OR MACHINE?

But increased mobility is only part of the story. Something more subtle, and possibly far-reaching, is also occurring: The line that has long separated human beings from the machines that assist them is blurring, as complex technologies become a visible part of the people who depend upon them.

Increasingly, amputees, especially young men like Clapp, and soldiers who have lost limbs in Afghanistan and Iraq, are choosing not to hide their prosthetics under clothing as previous generations did. Instead, some of the estimated 1.2 million amputees in the United States--more than two thirds of whom are men--proudly polish and decorate their electronic limbs for all to see.

Long an eerie theme in popular science fiction, the integration of humans with machines has often been presented as a harbinger of a soulless future, populated with flesh-and-metal cyborgs like RoboCops and Terminators. But now major universities like Carnegie Mellon and the University of California at Berkeley, as well as private companies and the U.S. military, are all exploring ways in which people can be enhanced by strapping themselves into wearable robotics.

"There is a kind of cyborg consciousness, a fluidity at the boundaries of what is flesh and what is machine, that has happened behind our backs," says Sherry Turkle, director of the Initiative on Technology and Self at the Massachusetts Institute of Technology, which studies technology's impact on humanity. "The notion that your leg is a machine part and it is exposed, that it is an enhancement, is becoming comfortable in the sense that it can be made a part of you."

While some users are eager to display their prosthetic marvels, others like them to appear more human. Besides selling prosthetics, Liberating Technologies, for one, offers 19 kinds of silicone sleeves for artificial limbs to make them seem more natural.

"There are two things that are important; one is functionality and the other is cosmetic," says Hanson, the company's president. "Various people weigh those differences differently. There are trade-offs."

But many young people, especially those who have been using personal electronics since childhood, are comfortable recharging their limbs' batteries in public and plugging their prosthetics into their computers to adjust the software, Hanson says.

Nick Springer, 20, a student at Eckerd College in St. Petersburg, Fla., who lost his arms and legs to meningitis when he was 14, recalls doing just that at a party when the lithium-ion batteries for his legs went dead.

"I usually get 30 hours out of them before I have to charge them again," he says. "But I didn't charge them up the day before."

TERMINATOR LEGS

When his legs ran out of power, he spent most of his time sitting on a couch talking to people while his legs were plugged into an electrical outlet nearby. According to Springer, no one at the party seemed to care, and his faith in his high-tech appendages appears unfazed. "I love my Terminator legs," he says.

Springer also remembers going to see Star Wars: Episode III--Revenge of the Sith with his father. While he liked the movie, he found the final scenes--in which Anakin Skywalker loses his arms and legs in a light-saber battle and is rebuilt with fully functional prosthetics to become the infamous Darth Vader--a little far-fetched.

"We have a long way to go before we get anything like that," he says. "But look how far humanity has come in the past decade. Who knows? The hardest part is getting the ball rolling. We pretty much got it rolling."

Michel Marriott is a business reporter for The New York Times.