Development and validation of a new observational method for assessing shoulder postural loading and musculoskeletal disorder risks

Abstract

The types and causes of work-related musculoskeletal disorders (WMSDs) vary by body part, and the shoulder is one of the most vulnerable sites. However, no observational method has been specifically developed to quantify the risk factors associated with shoulder WMSDs. Therefore, this study developed and statistically validated a new observational method, loading on shoulder assessment (LOSA), based on findings from previous studies. The shoulder WMSD risk factors implemented in this method were identified through a survey of the criteria used for evaluating shoulder postural stress, and were classified into a few classes, based on existing observational methods. Validation was conducted using discomfort ratings from 27 experimental postures and data from 53 real-world musculoskeletal disorder (MSD) cases. The developed method evaluates and integrates the effects of various shoulder WMSD risk factors, including shoulder motion, external load, motion repetition, static loading, coupling, working hours, and work experience, into a quantitative LOSA score, which is then categorized into four action levels to indicate the necessity and urgency of intervention. Validation results demonstrated that 1) LOSA score was strongly associated with perceived discomfort for 27 shoulder postures (r = 0.94, p < 0.01), 2) LOSA action category significantly affected work-related MSD classification (p < 0.01), and 3) LOSA category could well predict whether an MSD would be approved as work-related (p < 0.01). LOSA, developed to evaluate risk factors solely for shoulder WMSDs, is expected to assess their impact more accurately compared to existing observational methods, which typically focus on the entire body or arm- and hand-intensive tasks, thereby aiding the identification of shoulder WMSD risk factors in the workplace.