Another angle on the mouse discussion. All mouses have one thing in common. They require frequent use of the muscles that lift the arm (deltoid, trapezius, etc). Anyone experiencing regular stiffness or aches in the shoulder or neck would be well advised to consider using a trackball. It does not require as much use of the muscles mentioned, as the palm of the hand, and thus, the arm may remain at rest while the fingers do the work.
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