The influence of psychological stressors on myoelectrical signal activity in the shoulder region during a data entry task

Psychological stress is suspected to play a key role in the development of work-related musculoskeletal disorders (WMSDs), and work pace may be a primary contributor. The purpose of this study was to observe how psychological stress affects muscle activity recorded from key muscles used to support the shoulder (the trapezius and levator scapulae muscles) during keying tasks. We hypothesized that muscle activity [amplitude of the myoelectric signal (MES)] would increase and the number of periodic rests in muscle activity ('EMG gaps') would decrease when computer work was performed at an increased pace, and with distractions in the environment. Ten healthy volunteers performed three typing tasks (N=no stress; I=stress induced by a work pace reward; IS=stress induced by a work pace reward plus irritation/distraction). Both muscles showed significant increases ( p<.05) in MES amplitude when comparing IS to the N and I conditions, whereas N and I were not different. There was significant reduction in the number of gaps observed during the I and IS conditions (essentially no gaps were observed) as compared to the N condition. Interestingly, MES amplitude measures were capable of preferentially detecting changes in activation due to the distraction stress, whereas the number of EMG gaps preferentially detected the stress of the increase in work pace. The effect of these stressors on heart rate and productivity are also discussed.