For people addicted to typing messages on their handheld computers, the American Physical Therapy Association has released a series of hand exercises that can reduce the chances of developing "BlackBerry thumb."

The repetitive strain injury is caused by overuse of the thumbs to type messages on the popular BlackBerry e-mail device from Research In Motion, or any other handheld computer with a similar keyboard. "The thumb isn't a dexterous digit, so it's not used to working in this manner," Margot Miller, president of the Occupational Health Group for the APTA, said Monday.

Ignoring the discomfort from strained thumbs can lead to swelling and throbbing at the base joint and, in extreme cases, to Cortisone injections and surgery, Miller said.

To avoid this unpleasantness, APTA has released a series of hand exercises and stretches to increase circulation in the joint and relax thumb muscles. The simple exercises include tapping each finger with the thumb five times, and tapping the palm and back of each hand against the thigh as quickly as possible 20 times.

And, of course, putting the BlackBerry down to give the thumbs a rest occasionally is also advised.