The first time doesn't hurt.
Neither does the second, the fifteenth or the one hundredth time. But after repeating the same motion several thousand times, the human body often begins to feel the wear and tear. In fact, repetitive motion or repetitive stress injuries (RSIs) account for myriad work-related injuries every year. Sometimes the damage is so severe that the employee is no longer able to perform his or her job at all.
The Occupational Safety and Health Administration (OSHA) lists the three most common causes of RSIs: