The Relation between Stress, Muscle Activity, and Shoulder/Neck Pain: a Long-Term Field Study on Health Care Workers
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Background: Shoulder and neck pain (SNP) is one of the main causes for sick-leave, and the high prevalence affects occupations with both high, moderate and low workloads. At present, the knowledge about pain mechanisms in occupations with low physical workload is still limited. The main purpose of this study was to investigate whether perceived work stress during the workday is related to trapezius muscle activity. A second objective was to investiagte whether trapezius activity differs between individuals with long-term SNP. Methods: Twenty-seven female health care workers participated. Surface electromyography (sEMG) was recorded from the trapezius muscle throughout the workday. Simultaneous inclinometer recordings of the thigh was used to identify periods with sitting, standing, and walking. SNP and stress were recorded by visual analogue scale and physical fatigue by Borgs scale every hour throughout the workday. An index for long-term SNP was also calculated. Findings: Two main comparisons were performed: A between group comparison where sEMG in pain-afflicted workers was compared to sEMG recorded from pain-free workers, and an intra-individual comparison where sEMG in periods of high stress was compared to periods of low stress. In the analyses of the sEMG activity pattern, the focus was on median amplitude and rest time defined as activity < 0.5% of the maximal sEMG response. Overall, there was no evidence of a difference in sEMG activity between pain-free and pain-afflicted workers. Neither did sEMG activity differ between periods with high vs. low stress. Interpretation: The current study does not support the hypothesis that SNP is related to stress-induced low level muscle activity. Further research is needed to reveal the relation between stress, muscle activity and SNP, and the mechanisms behind.