Research article
Physiological responses to low-force work and psychosocial stress in women with chronic trapezius myalgia
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* Corresponding author: Anna Sjörs anna.sjors@liu.se
1 Rehabilitation Medicine, Faculty of Health Sciences, Linköping University, SE 581 85 Linköping, Sweden
2 Pain and Rehabilitation Centre, University Hospital, SE 581 85 Linköping, Sweden
3 Department of Rehabilitation, School of Health Sciences, Jönköping University, Box 1026, SE 551 11 Jönköping, Sweden
4 School of Occupational Therapy and Social Work, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia
BMC Musculoskeletal Disorders 2009, 10:63 doi:10.1186/1471-2474-10-63
Published: 7 June 2009Abstract
Background
Repetitive and stressful work tasks have been linked to the development of pain in the trapezius muscle, although the underlying mechanisms still remain unclear. In earlier studies, it has been hypothesized that chronic muscle pain conditions are associated with imbalance in the autonomic nervous system, predominantly expressed as an increased sympathetic activity. This study investigates whether women with chronic trapezius myalgia show higher muscle activity and increased sympathetic tone at baseline and during repetitive low-force work and psychosocial stress, compared with pain-free controls.
Methods
Eighteen women with chronic trapezius myalgia (MYA) and 30 healthy female controls (CON) were studied during baseline rest, 100 min of repetitive low-force work, 20 min of psychosocial stress (Trier Social Stress Test, TSST), and 80 min recovery. The subjects rated their pain intensity, stress and energy level every 20 min throughout the experiment. Muscle activity was measured by surface electromyography in the trapezius muscle (EMGtrap) and deltoid muscle (EMGdelt). Autonomic reactivity was measured through heart rate (HR), skin conductance (SCL), blood pressure (MAP) and respiration rate (Resp).
Results
At baseline, EMGtrap, stress ratings, and HR were higher in MYA than in CON. Energy ratings, EMGdelt, SCL, MAP and Resp were, however, similar in the two groups. Significant main group effects were found for pain intensity, stress ratings and EMGtrap. Deltoid muscle activity and autonomic responses were almost identical in MYA and CON during work, stress and recovery. In MYA only, pain intensity and stress ratings increased towards the end of the repetitive work.
Conclusion
We found increased muscle activity during uninstructed rest in the painful muscle of a group of women with trapezius myalgia. The present study could not confirm the hypothesis that chronic trapezius myalgia is associated with increased sympathetic activity. The suggestion of autonomic imbalance in patients with chronic local or regional musculoskeletal pain needs to be further investigated.