The following tips can help you avoid a mouse-related musculoskeletal injury. The same posture principles apply to other input devices (e.g,. trackball, touchpad, pen, digitizing puck etc.).
Mouse grip: Hold the mouse gently to move it over a mousing surface.
Mouse from the elbow: Don't skate or flick the mouse with your wrist. Make controlled mouse movements using your elbow as the pivot point and keep your wrist straight and neutral.
Optimal mouse position: Sit back in your chair, relax your arms then lift your mousing hand up, pivoting at the elbow, until your hand is just above elbow level. Your mouse should be positioned somewhere around this point. Don't use a mouse by stretching to the desk or out to the side of a keyboard.
Right-handed users: Use a position-adjustable, flat-mouse platform and adjust this to a position that is one to two inches above the keyboard and over the numeric keypad; you can easily move the platform out of the way if you need to access the numeric keypad keys. If you need to access the numeric keypad or if you do not have space for an over-the-keyboard mouse platform, then use an angle-adjustable mouse platform that is immediately to the right side of the keyboard. Position this mouse platform so that it slopes downwards and is close to the side of the keyboard; this will enable you to use the mouse in a neutral wrist position. Position adjustable mouse platforms are commercially available.
Left-handed users: If you are using a left-handed keyboard with the numeric keypad on the left side, you can use an over-the-keyboard mouse pad as described above. If you want to mouse with your left hand but have a right-handed keyboard, then you do not need to use an over-the-keyboard platform because this will obscure some of the alphabetic keys. In this situation it is best to use an angle-adjustable mouse platform that is immediately to the left side of the keyboard, and to position this platform so that your left wrist is neutral as described above.
Protect your wrist: The anatomy of the wrist is curved away from any contact surface. (You can easily see this by resting your hand/arm on a flat surface—you'll see light under the wrist and can probably even pass a thin pen under it.) The forearm is shaped liked this for the wrist to remain free of surface-pressure contact.
Avoid restricting circulation: For many people there are exposed blood vessels near the skin at the wrist, which is where the pulse is often taken. Any pressure in this region will disrupt circulation into the hand and this will increase the risks of injury.
Don't use a wrist rest: Research has shown that using a wrist rest doubles the pressure inside the carpal tunnel, because the floor of the tunnel is a more flexible ligament that transmits external pressure changes directly into the carpal tunnel. (The roof of the tunnel is bone, so the pressure doesn't get transmitted on through the hand.) Indeed, one test for carpal tunnel syndrome (CTS), know as Tinel's sign, simply involves tapping on the palm surface of the wrist, which is enough to cause tingling and numbness in someone developing CTS.
Avoid restricting arm movement: With a softly padded wrist rest (especially one that is rounded) or a soft chair armrest, the forearm becomes locked into position. This encourages people to make mouse movements by flicking their wrists, which also increases intracarpal pressure.
Keep the mouse free-moving: The base of the palm is the part of the body designed to support the hand when resting on a surface. For keyboard use a broad palm support is best. However, mouse use is different than keyboard use. With a keyboard the best posture is for users to float their hands over the keyboard when typing and then to rest on the palm support in micro breaks between typing bursts. With mousing this doesn't happen. A mouse is used by moving its location over a surface, and resting usually occurs when mouse movements stop but with the mouse still being held in the hand. Mouse movements should be made using the elbow as the pivot point, not the wrist. Anything that impairs free movement of the forearm/hand and mouse will increase injury risks.
Mouse shape: Choose a mouse design that fits your hand but is as flat as possible to reduce wrist extension. Don't use a curved mouse. Use a symmetrically shaped mouse. Consider a larger mouse that encourages arm rather than wrist movements.
Load sharing: If you want to load share between your right and left hands, that is using the mouse for some of the time with each hand. For this you need to choose a mouse platform that can easily be configured to the left or/and right or a keyboard platform that can accommodate two mouse platforms, and a symmetrical shaped mouse that can be used by either hand.
Other input devices: Whether you choose a different mouse design, a trackball, a joystick, a pen, a touch pad or some other input device, make sure that your position this comfortably, and that your wrist is in a neutral position when using the device.