Physical and mental strain at work: Relationships with onset and persistent of multi-site pain in a four-year follow up

- Attention to work exposures and musculoskeletal disorders is increasing.
- Mental strain at baseline was a strong predictor of persistence of multi-site pain.
- The association was more prominent among older employees.
- Psychosocial exposures at work is important in workplace intervention.

This study evaluates the association of physical and mental strain with the onset and persistence of multi-site musculoskeletal pain among younger and older employees in four-year follow-up. A questionnaire survey was conducted twice in a food processing company, in 2005 and 2009, with responses from 734 employees (445 younger and 289 older; 65% female). Information on musculoskeletal pain during the preceding week and perceived mental and physical strain was obtained through a structured questionnaire. The association of onset and persistent of multi-site pain with mental and physical strain was estimated with log binomial regression analysis and stratified by age group. Risk ratios (RR) with their 95% confidence intervals (CIs) are reported for the estimates. More than 56% of the employees reported multi-site pain at baseline. Among those who reported multi-site pain at baseline 70% reported persistent multi-site pain and one-third reported new onset of multi-site pain at follow-up. Mental strain at baseline strongly predicted persistence of multi-site pain among both younger and older employees (RR from for younger employees = 1.68, 95% CI = 1.01-2.83 and RR for older employees = 2.25, 95% CI 0 1.27-3.98) but the association with physical strain was not statistically significant. Mental strain predicted the risk of persistence of multi-site pain among both younger and older employees in four-year follow-up but not onset of multi-site pain.Relevance to the industryThe results of this study suggest that monitoring working conditions of all age workers can reduce physical and mental strain, thereby reducing the incidence of multi-site musculoskeletal pain and promoting workers' health.