Cumulative Trauma Disorder (CTD) is a condition of the muscles in the wrist, forearm, arm and neck that is caused by their overuse (or misuse) at work. The muscles of the upper limbs are not designed to hold specific positions for a long time, nor to do the same activity repeatedly.
If these muscles are performing these activities constantly (working against their design), then the muscles release a waste bi-product (acid) as they are forced to produce energy without sufficient oxygen. It is a build up of these bi-product chemicals in specific areas that signal pain, muscle spasm, tenderness and the need to stop the activity causing the muscles to become aggravated.