Load pattern and pressure pain threshold in the upper trapezius muscle and psychosocial factors in medical secretaries with and without shoulder/neck disorders

Object: A current hypothesis for the genesis of muscular complaints in the shoulder/neck region postulates that short periods with a completely relaxed muscle are essential to avoid complaints. Another hypothesis is that these disorders are related to psychosocial conditions at work. In order to test these hypotheses, 23 medical secretaries were investigated. Methods: The load pattern during work in the upper trapezius muscle bilaterally was assessed with electromyographic (EMG) technique and exposure variation analysis (EVA). In addition, pressure pain threshold (PPT) was measured on the trapezius muscle bilaterally and on the sternum. Psychosocial conditions at work were assessed with a questionnaire. Results: The medical secretaries with complaints had significantly fewer episodes with totally or close to totally relaxed muscle compared with the healthy group. The group with complaints tended to have a more monotonous load pattern at low load levels (approx. 1%-5% maximum voluntary contraction) while the healthy group had more frequent pauses but also somewhat more frequent short load peaks. The group with complaints showed lower PPT readings compared with the healthy group. However, the whole group had considerably lower PPTs than is usually reported in the literature. Of the 12 questions in the psychosocial questionnaire only one regarding work task satisfaction showed a significant difference between the two groups. Conclusion: Support is found for the hypothesis that secretaries without complaints have more frequent episodes with totally relaxed muscle. A significant difference is found regarding work task satisfaction.