[Psychogenic muscular activity as a risk factor of muscular pain].

Recent research indicates that any continuous load on the shoulder and upper limb muscles is a risk factor for occupational muscle pain. When the muscle load is moderate to low, the duration seems far more important than the actual load level, possibly because of a fixed recruitment order of motor units. Research at the Norwegian National Institute of Occupational Health has shown that a mentally challenging task at a visual display terminal may give a low level of muscle activation with apparently no purpose as regards posture or movement ("psychogenic" muscle tension), based on continuous firing in a few motor units. This indicates a possible mechanism for the often observed link between psychosocial stress and muscle pain.