Alternate Input Devices

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Using a mouse, with the hand in the pronated position can cause repetitive stress injuries or Occupational Overuse Syndrome. Think of how you naturally grasp tools. Even if you grasp a rock to smash something, it is easier to wrap your hand around it and pound up and down with your wrist than to cup it in your palm and smash up and down with your elbow. Another problem that causes discomfort of the arm is when the mouse is to the side of an already off center keyboard because of the navigation keys and number pad. “7.16 Frequent or prolonged bending and twisting of the wrist from the neutral (natural) position increases the risk of injury.” (1) The natural position of the hand is thumb up, heal of the hand down on the table, palm facing the center of the body and fingers lightly curved

The external rotation of the shoulder and ulnar deviation of the wrist problems with the mouse can be addressed with better placement. Experts suggest that the pointing device be between the keyboard and you, some suggest it be on a riser above the number keys, and some keyboards have the number pad on the left, to give your left hand something to do and move the mouse closer to the centerline.

There are several innovations to solve the pronation problem. From most traditional to least: Designer Appliances Inc makes the AirO2bic mouse, that rests the heal of the hand in a groove and leaves the palm vertical. (2) Evoluent makes a wide mouse, it looks almost like a steam iron that keeps the wrist in a neutral position and does not demand a power grip like smaller flat mice do. (3) This reduces some of the muscle strain. The next, but still mouse like device is the ‘mouse on a stick’, the hand is now in a neutral position and the mouse buttons are on the top of the stick to be used by the thumb, which is naturally stronger than the fingers. These are made by Anir and 3M. (4)(5)

The next step in the progression is a jump: touchpads, pens and pointers. Touchpads, either built into the keyboard or accessories in the mouse position move the hand back into pronation. For example the Cirque SmartCat (6). Pen devices are held like a pen, with the hand in a neutral position, with fine motion controlled by the fingers the way we naturally draw and write. (8) This reduces almost all shoulder and elbow work by limiting the distances moved and yet restores control of the cursor by giving it to the fine finger muscles. (7) Further evolution, away from the desktop to the light pen, and touch screen, returns to muscle strain patterns. The screen selection devices reduce mental processing because the item chosen is the item you point to, but physical strain rises because the whole arm has to be held up and the fine motion of selecting now is done with the back, shoulder, elbow and wrist besides a small component of finger movement. This is simpler but not easier.

Conclusion: We have begun to exceed the human body’s ability to adapt with large workspaces and numerous peripherals. Using a pen pad restores the right hand to a neutral position, returns the fine control to the fingertips the way we use pens and pencils now, and improves accuracy and speed (8).








8. Kentaro Kotani1 and Ken Horii. An Analysis of Muscular Load and Performance in Using a Pen-tablet System. Journal of PHYSIOLOGICAL ANTHROPOLOGY and Applied Human Science. Vol. 22 (2003) , No. 2 pp.89-95

Michael Kordek