When in a  sitting position for a long time, muscles are exposed to considerable overstrain, especially the trunk muscles stabilizing the spine, but also the hand and arm muscles.

An incorrect sitting position makes the muscles contract or stretch, depending on their location. The paraspinal muscles are stretched when in a sitting position for a long time and become weaker. The abdominal muscles also become weaker, especially the straight muscle of the abdomen.

Muscles of other parts of the body, like the hand, are exposed to repetitive movements while working with a computer. These muscles require very strong contractions over many hours of work, which leads to tenderness and limitation of mobility in the area or increased rigidity of the structures. A frequent abduction of the thumb associated with ulnar deviation of the wrist (occurring while using a keyboard) may lead to de Quervain’s disease- a constricting inflammation of the tendon sheath within the first dorsal compartment of the wrist. It is the dorsal compartment of extensors, situated the furthest to the radial side of all six dorsal compartments of the wrist. It involves tendons of the long abductor muscle of the thumb and the short extensor muscle of the thumb in the area of the styloid process of the radial bone. The symptoms of this disease include pain and swelling of the radial side of the wrist and thumb. Movements of the thumb may cause considerable intensification of pain. Finkelstein’s test is useful in diagnosing de Quervain’s disease. The test includes flexion of the thumb and setting it across the palm, and next, flexion of the other fingers so that they embrace the thumb. In this position the movement of ulnar adduction of the wrist should be performed. A very strong pain is a manifestation of the disease. However, even in a healthy hand less intense painful sensations may appear. This disease should be differentiated from degenerative disease of the carpal-metacarpal joint of the thumb, which may occur concomitantly with de Quervain’s disease.

A devastating effect of work involving repetitive movements is called RSI - Repetitive Strain Injury. This term is related to a condition caused by working with a keyboard and computer mouse. RSI is not regarded as a diagnosis - this name is used to describe pain which occurs while working and it always refers to pain of musculoskeletal origin. Monotonous movements during the whole day initially lead to mild ailments, which are usually ignored or controlled with painkillers. After a longer period of such overstraining work without proper medication, considerable tenderness and intensification of complaints occur. RSI may appear on one or both sides of the body, substantially hindering normal activity.

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