There are other ways to move electronic arms, including position sensors, so shrugging a shoulder can trigger it. Or a force sensor, a metal piece that reads force across the shoulders. You can even press on a touchpad. Many people born without limbs have what's called a "vestigial finger," and the arm can be designed so that "finger" can run it inside the arm.

Initially, the challenge was creating components small enough but powerful enough to get the job done. These days, tiny off-the-shelf components are readily available. It's the evolution of technology. Early computer processors took up entire rooms. Now much more powerful processors fit easily in your hand.

The newest version of the Utah artificial arm, called the U3, is a dual computer system with two processor chips in the elbow, one to run the hand and the other the elbow. The advantage of the multiple-control device, unique to the U3, is it can control the hand and elbow at the same time.

Kevin Hays, electronic engineer at Motion Control, saw a powerful demonstration of that recently at Walter Reed Hospital, where many soldiers injured in Iraq have been fitted with new limbs.

Hays saw a patient pick up garbage with his artificial hand and arm. "He let his elbow down, then brought the elbow up and let his hand relax in one fluid motion. Jaws hit the floor to watch him do it. Normally, you'd bring it up, position it and wait to lock it in place."

But it's bittersweet, Hays said. For all the improvements over the past two decades, the technology does not yet exist to move individual fingers. He's not sure he'll see it in his lifetime.

Iversen said future improvements will likely be incremental. They're trying to make arms and hands that are quieter. And faster, without sacrificing strength. They dream of an arm that will be waterproof. It's marginally water resistant, so when he washes dishes, Whitten's careful not to fill the sink too full. He wears rubber gloves. He removes his arm to swim. Should he lose his footing and fall into the pool, it would be ruined.

"We want to make them more rugged, more shock-resistant, more reliable," Iversen said.

Motion Control is field-testing a system that provides feedback about force. It has a device that pushes on the user as hard as he's squeezing. It's not needed often, one user said, but there are times it would help. He worries when he's playing with his children. The hand squeezes with about 20 to 25 pounds pressure, something a human hand does not do.

That extra force is needed because the hand has no adaptable grab. Most people can grab something by cradling it, but a prosthetic hand has to squeeze, and that takes more strength.