depending on what motion you are doing with the mouse, from careful aiming through to whipping right round in circles with the mouse coming off the surface, you

depending on what motion you are doing with the mouse, from careful aiming through to whipping right round in circles with the mouse coming off the surface, you end up using everything from your fingers to your shoulder. Up and down (away and toward) motions are generally shoulder motions, for instance, unless they are very slight, as otherwise you arch your hand too far off the mouse.