One of the results of this new work pattern is an increase in the number of painful conditions involving the back, neck, wrist and head. The major factor contributing to these injuries is the long period of time an employee sits in the chair. Another is the increase in repetitive motions required with the use of keyboards. The arrangement of lighting and VDT screens also contributes to the incidence of work-related complaints. Both contribute to pain in the back and neck.
Static effort occurs when a muscle is contracted and held in the contracted position for some time.
Bloodflow is restricted in a contracted muscle. Dynamic effort, such as walking, is easy to sustain for long periods of time because fresh, oxygenated blood flows in a muscle every time it releases. Static effort, however, results in a continual deficit of blood supply to the contracted muscle, so a statically held muscle cannot rid itself of metabolic waste products. It is these waste products which produce the feelings of pain, tenderness and fatigue. Most jobs have a combination of dynamic and static effort tasks.