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.