The wheelchair that had been Lucy Spruill's friend for 30 years - helping her on the way to a master's degree, a career, a home and a family - had turned against her.

Three decades of cranking the wheels of her chair had gradually torn the tendons in both shoulders. She learned the bad news three years ago, at age 50."I couldn't raise my hands to comb my hair," she said. "I couldn't push myself without extreme pain."

She's not alone. When it comes to repetitive stress injuries, wheelchair users have typists beat by a mile. They grip and push wheel rims day in and day out, pinching nerves and damaging tendons.

"Most of the patients are people who are fighters, and they've overcome a disability, and it's like being hit with another one," said Dr. Michael Boninger, medical director of the Human Engineering and Research Lab at the University of Pittsburgh. "They go from being totally independent to being totally dependent."

A study under way at the lab is an attempt to help doctors and therapists provide better training for wheelchair users by analyzing techniques. Until now, lab director Rory Cooper said, the attitude has been that "pain is part of the ticket of using a wheelchair. Get used to it."

About 1.5 million Americans use wheelchairs. Studies show half end up with carpal tunnel syndrome - the compression of the medial nerve at the wrist. Boninger said shoulder injuries such as rotator cuff tendinitis or tears can injure just as many; some suffer from both injuries.

Proper technique can help, but few are taught, said Justin Craig, assisted technology coordinator for the Eastern Paralyzed Veterans Association in New York.

"They say, `Here's your wheelchair, here you go.' They might tell you to watch your knuckles when you go through the doorway," Craig said.

He suggests better hand positions, and exercises to help prevent strain injuries. Cooper advises people push with wrists straight and elbows close to the side to avoid making "chicken wings" with their arms. Adjustable wheels and lower back support help, too.

The 40-person, decadelong study - the largest of its kind - is expected to better determine the best positions. It is funded by the National Institutes of Health.

Wedge-shaped computers between the spokes measures the amount and direction of force applied by the user's hand. The hands, arms and shoulders are wired with infrared sensors to monitor movements and positions as the person pushes.

"I won't ever be able to use a manual wheelchair full time," said Spruill, who now uses a power wheelchair - which costs more, is difficult to move in and out of vehicles and, experts say, can make the user feel more dependent.