LOS ANGELES, California (AP) -- Chris Claypool was addicted to his BlackBerry wireless handheld. Like many users, he never thought twice about pecking away at lightning speed, replying to a wave of e-mails from clients around the globe.

Last year, the 37-year-old agricultural sales director from Post Falls, Idaho, noticed a throbbing sensation in this thumbs whenever he typed. He switched to tapping with his index finger, then his middle digit and finally his pinky. But his thumbs pained him to the point where he can't even press the buttons on his TV remote control.

After months of aching, Claypool took a break. Now he only uses his BlackBerry to send short messages -- typing with the tip of a pencil eraser whenever his thumbs get sore.

"It affects business because I can't whack away on my BlackBerry like I used to," he said. "It's just too painful."

Repetitive motion injuries, which have long afflicted desktop and laptop computer users, are invading the mobile handheld world.

There's even an informal name for the malady -- "BlackBerry Thumb" -- a catch-all phrase that describes a repetitive stress injury of the thumb as a result of overusing small gadget keypads.

Business executives and tech-savvy consumers are increasingly using BlackBerries, Treos, Sidekicks and other devices with miniature keyboards designed for thumb-tapping to stay connected while on the go.

And that has some ergonomic and hand experts worried about injuries from overexertion.

"If you're trying to type 'War and Peace' with your thumbs, then you're going to have a problem," warned Alan Hedge, director of the Human Factors and Ergonomics Laboratory at Cornell University in Ithaca, New York.

No national statistics exist on how many people suffer from this type of thumb ailment, but some doctors say they are seeing an upswing in related cases, said Dr. Stuart Hirsch, an orthopedist at St. Joseph's Hospital and Medical Center in Paterson, New Jersey.

"It's mostly the road warrior who prefers to answer e-mails on a thumb keyboard," said Hirsch. "If all you did was just answer with a simple yes and no, it would not be a dilemma."

For as long as video gamers have been blasting aliens, so-called "Gamer's Thumb" has been a sore spot for them, as well. With tens of millions of portable video game machines on the market, lots of young hands risk digit abuse.

Games for such devices generally include some type of printed warning about injury risks from prolonged playing.

Earlier this year, the American Society of Hand Therapists issued a consumer alert, warning users of small electronic gadgets that heavy thumb use could lead to painful swelling of the sheath around the tendons in the thumb.

The group recommended taking frequent breaks during e-mailing and resting one's arms on a pillow for support.

A booklet that ships with the Nintendo DS handheld system advises a 10 to 15 minute break for each hour of play, and a break of at least several hours if gamers experience wrist or hand soreness.

"People tend to use just one finger over and over again and it's that repetitive use with one digit that could lead to problems," said Stacey Doyon, vice president of the American Society of Hand Therapists and a registered occupational therapist in Portland, Maine.

The BlackBerry, which debuted in 1999, employs a full QWERTY keypad for thumb typing to automatically send and receive e-mail. About 2.5 million people currently use Blackberries, more than double from a year ago.

An executive for Research In Motion Ltd., which makes the BlackBerry, said the company considers ergonomic factors when designing its keyboards.

"Of course, any product can be overused ... so people should listen to their own bodies and adjust their routine if necessary. But I would caution against confusing rare examples of overuse with the typical experience," Mark Guibert, vice president of marketing, wrote in an e-mail.

Musculoskeletal disorders, which include repetitive strain injuries, accounted for a third of all workplace injuries and illnesses reported in 2003 -- the latest data available, according to the U.S. Bureau of Labor Statistics.

Specialists say the thumb -- considered by many as an island because it is set apart from the other fingers -- is among the least dexterous digit and is not meant to be rigorously worked out.

For people who insist on typing more than a sentence with their thumbs, external keyboards that connect to the gadgets may be a less painful alternative, said Dr. Jennifer Weiss, assistant professor of orthopedics at the University of Southern California in Los Angeles.

Treatment for BlackBerry thumb may include wearing a splint and applying ice to the affected area. If the pain persists, doctors may opt to inject the thumb area with a cortisone shot. Surgery may be required as a last resort.

John Orminski, a 44-year-old information technology manager from Pontiac, Michigan, went to a doctor in the spring after feeling a strain in his right thumb.

On any given day, Orminski uses his thumb repeatedly to punch clients' telephone numbers, scroll through his address book and update his calendar on his BlackBerry.

Orminski already suffers from golfer's elbow -- a form of tendinitis -- from playing the sport. But unlike his elbow pain, which occurs in spurts, Orminski's thumb woes tend to flare up more often.

He recently started physical therapy for this thumb -- receiving electrical stimulation and massage to relax the muscles.

"It can get sore and tender, but I'm learning to live with it."