The classic posture for computer work suggests the chair lean back 20-30 degrees, and the work surface is positioned two inches below the elbow. The keyboard is positioned at the front of the desk to allow the forearm to “float” over the keyboard for easy motion.
When the body is relaxed, and the torso is leaning back against the chair, the pelvis lines up with the head, and the spine is in good position.
When dedicated keyboard work begins to include other tasks on the work surface, like writing, calculator or telephone, the shoulder reach may draw the body forward.
When there is greater interest to the monitor or other visual targets on the work surface the head is also drawn forward, and the torso begins to collapse.
Resting postures may not be very easily supported, and the arms may unload on the front of the work surface, or the wrist may be support the weight of the arm at the carpal tunnel on the wrist pad.
When the body is relaxed, and the torso is forward, the pelvis points away from the head, and the spine is in a very bad position.