CAN STRESS-RELATED SHOULDER AND NECK PAIN DEVELOP INDEPENDENTLY OF MUSCLE-ACTIVITY

A case-control designed was used to investigate associations and inter actions between muscle activity measured by surface electromyography ( EMG) in the upper trapezius muscle and subjectively reported risk fact ors in workers with and without shoulder and neck pain. EMG data were collected both in the workplace (indicating vocational muscle activity ) and in a laboratory setting (indicating non-specific muscle activity ). Women in manual (15 pairs) and office (24 pairs) work were included , The pairs were matched on age, gender and on current and historical work load, such as working hours, type and length of employment. Previ ous reports of this study have indicated that shoulder and neck myalgi a was associated with increased muscle activity for the manual workers , and with psychological and psychosocial factors for the office worke rs. These risk factors were in the present report used as the basis fo r studying associations and interactions between muscle activity (1), psychological and psychosocial factors (2), and shoulder and neck pain (3). Subjectively reported or perceived general tension, a stress sym ptom presumed related to psychosocial and psychological factors, was p reviously found to be the strongest and only variable separating cases and controls in both work groups. In this paper, no relationship was found between perceived general tension and EMG variables for the offi ce workers. For the manual workers a strong interaction was found; per ceived general tension correlated positively with EMG variables for th e controls, and negatively with EMG variables for the cases. It is hyp othesised that the feeling of general tension represents a physiologic al activation response that may or may not include muscle fibre activa tion. This implies that pain provoked by psychosocial stress factors m ay not be mediated through increased muscle activity.