Background
China's manufacturing industry is still labor-intensive, and assembly employees in manufacturing industry are facing a great risk of work-related musculoskeletal disorders (WMSDs).
Objective
To investigate and analyze the prevalence and distribution of WMSDs among assembly workers in manufacturing enterprises and explore the relationship between WMSDs and ergonomic exposure factors such as posture load and mental load.
Methods
From July to September 2017, by convenient sampling, a cross-sectional survey was conducted to select 670 workers engaged in electronic accessories assembly and railway vehicle manufacturing in three manufacturing enterprises in two cities in northern China as the research participants. The posture load assessment was based on the Chinese Musculoskeletal Questionnaire independently developed by our research group. The mental load assessment was based on a revised Chinese version of the Subjective Workload Assessment Technique. An unconditional logistic regression model was used to explore the relationship between ergonomic exposure and WMSDs.
Results
The overall prevalence rate of WMSDs was 39.6% (265/670) with 43.8% in males and 25.2% in females; the highest prevalence rate was 47.7% in the group aged 40 years and over. The prevalence rate of WMSDs in the electronic accessories assembly workers was 16.9%, that in the railway vehicle manufacturing workers was 57.3%, and the difference was statistically significant (
\chi ^2 
=112.63, P<0.001). The mental load score median (first quartile, third quartile) was 55.6 (51.9, 83.3) points, and the posture load score was 27.1 (16.0, 41.5) points. The results of unconditional logistic regression model showed that women (OR=3.152, 95%CI: 1.458-6.813), drinkers (OR=1.934, 95%CI: 1.124-3.326), and railway vehicle manufacturing worker (OR=3.416, 95%CI: 1.756-6.644) had a higher risk of reporting WMSDs; The higher the mental load (OR=1.019, 95%CI: 1.007-1.031) and posture load (OR=1.034, 95%CI: 1.019-1.050), the higher the risk of reporting WMSDs. The hierarchical analysis results showed that the risk of reporting WMSDs was higher among the electronic accessories assembly workers who were older (compared with those aged <30 years, OR30-39=2.526 and OR≥40=12.263, respectively) and with higher posture load (OR=1.025, 95%CI: 1.002-1.049), as well as among the railway vehicle manufacturing workers who were drinking (OR=2.035, 95%CI: 1.155-3.583), obese (OR=3.094, 95%CI: 1.185-8.078), with higher mental load (OR=1.013, 95%CI: 1.001-1.025) and posture load (OR=1.033, 95%CI: 1.018-1.049).
Conclusion
There is a significant correlation between reporting WMSDs and ergonomic exposures such as posture load and mental load, and drinking is also a risk factor of WMSDs. The risk of reporting WMSDs in female workers in assembly manufacturing industry is higher than that in male workers. The overall prevalence rate of WMSDs in railway vehicle manufacturing workers is higher than that in electronic accessories assembly workers.
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