RSI originates from repeating the same activity over a period of time that might lead to physical complaints. Currently, new terminology is used, namely CANS (Complaints of the Arm, Neck and Shoulder), but for explanatory purposes, we will refer to RSI.
Example of RSI: The use of a computer mouse is in itself light effort. However, you continuously use the same muscle and joint on the same arm to manoeuvre the mouse around. These structures then become overloaded and present as RSI.