PSYCHOLOGICAL STRESS AND MUSCLE-ACTIVITY DURING DATA-ENTRY AT VISUAL-DISPLAY UNITS

The aim of this study was to evaluate whether psychological stress cau ses increased muscle activity, especially static muscle activity, in t he trapezius muscles of the neck and shoulder. A pilot and a main stud y were carried out with 10 males and 20 females, respectively. The sub jects performed a VDU data entry task under psychologically stressful and non-stressful conditions. Stress reactions were measured by differ ent methods: heart rate and heart rate variability, hormonal excretion , and subjective ratings of mood and body symptoms. The stress conditi on caused an increase in heart rate. The low-frequency variability inc reased and the high-frequency variability decreased. Ratings of motiva tion and relaxation decreased, and subjects felt more activated. Pain and discomfort from the stomach increased. Adrenaline and noradrenalin e in urine were unaffected. The majority of the subjects showed modera tely increased static and median EMG levels during the stress conditio n. The interindividual variation In muscular reactions was large. Stat istically significant increases were obtained for the myoelectric acti vity of the left (resting) trapezius muscle when pooling the two group s. It appears that the increase in muscle activity due to this type of mental stress is small, and factors other than 'attention-related' lo ad may be more important. The results indicate that some individuals m ay be more prone to general muscle tension, making them more likely to develop symptoms and musculoskeletal pain.