Background: Lateral epicondylitis (LE) is a highly prevalent musculoskeletal disorder in workers, often associated with physically demanding work. Knowledge of workrelatedness of LE is crucial to develop appropriate preventive measures. This study investigates the prospective association between work-related physical risk factors and LE. Methods: A systematic literature review was conducted in MedLine using PubMed from January 1, 2010 until February 16, 2021. Published reports were included if: (1) LE was clinically assessed, (2) exposure to work-related physical risk factors was assessed, and (3) associations between LE and work-related physical risk factors were reported in prospective studies. Quality of evidence was assessed using the Grading of Recommendations, Assessment, Development and Evaluation. Results: In total, 318 workers with LE from a population of 5036 workers in five studies were included. Meta-analyses revealed high-quality evidence for associations between LE and a Strain Index (SI) score >5.1 (odds ratio [OR]: 1.75, 95% confidence interval (CI): 1.11-2.78) and moderate-quality evidence for forearm rotation >4 h/day or forearm rotation ≥45°for ≥45% time (OR: 1.85, 95% CI: 1.10-3.10). Gripping, flexion and extension of the wrist, and repetitive movements showed no significant associations with LE. Conclusion: High-quality evidence was found indicating that a higher SI increased the risk of LE. Moderate-quality evidence was found for an association between forearm rotation and LE. No associations were found between other physical risk factors and LE. Primary preventive interventions should focus on a reduction of the SI and of high forearm rotation in work.
Determination of individual maximum voluntary contraction (MVC) force is used as the gold standard for normalising surface EMG (SEMG) data. Assuming a linear amplitude-force relationship, individual strain levels are defined according to percentage rates of the measured MVC levels. The purpose of the study was to investigate if the assumed force-strain relationship can be applied without qualification. Therefore, healthy volunteers (nine men, ten women) were investigated during isometric exercises of shoulder muscles at MVC and 50% levels. Tasks were performed at four different angular positions in frontal, sagittal and horizontal planes. In each plane, both possible force directions were investigated. SEMG was taken simultaneously from 13 muscles of the shoulder and upper arms from both sides of the body. At a force level of 50% MVC, SEMG amplitude levels were compared to the expected 50% level. Differences in muscular co-ordination patterns were also determined. During retroversion and horizontal flexion, amplitude levels significantly remained at levels below 50%. This was seen for all the muscles investigated, independent of relative contribution to force production. During horizontal extension and abduction, the main force-producing muscles showed amplitude levels that significantly exceeded the expected 50% level. Co-ordination patterns differed significantly between MVC and submaximal conditions for anteversion, retroversion and horizontal extension. Specifically, four shoulder muscles showed higher proportions at the 50% level compared to MVC. Therefore, certain percentage rates of MVC force levels exhibit quite different strain rates, as identified by SEMG. Depending on force direction, differences in co-ordination patterns exist between MVC and submaximal test conditions. Both findings have implications for therapeutic and training applications.
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