Pianists actually move their arms and hands much more than typists. Computer operators use different repetitive motions and keystrokes than pianists. On the computer keyboard, you will rarely stretch the thumb and little finger apart to reach the keys. But for some people, stretching an octave plus a chord on the piano stretches the hand maximally.

It's also true with most computer keyboards that the pressure needed to strike a key is far less than the pressure needed to depress a piano key to make a sound. The computer keyboard operator uses about the same amount of pressure on each key every time. The pianist is more likely to strike with power and force to produce the sound required by the music.

Finally, wrist motion is different between the two activities. On the piano, the player may have to tilt or rotate the wrist more and more often compared to using a computer. There's also greater risk of injury or overuse on the piano for players with smaller hand size or hand span.