Paced Manual Work Variations and Exposure to Risk Factors of Work-related Musculoskeletal Disorders, WMSDs

Research Trainee: Vernnaliz Carrasquillo, PhD Student, Dept. of Industrial and Operations Engineering at the University of Michigan

Faculty Researcher:Thomas J. Armstrong, PhD., Professor of Industrial and Operations Engineering at the University of Michigan

There has been much progress identifying and controlling exposure to work-related factors of upper limb musculoskeletal factors. Still, work-related musculoskeletal disorders, WMSDs, continue to be an important cause of work disability. We hypothesize that even when jobs are designed so as to minimize WMSD, risk factors can result from equipment, material, process, and work method variations in manufacturing jobs. This work will develop computerized models that can be used study the relationship between work variations and posture, hand force and recovery time. Work variations and associated exposures may not be apparent because they may occur at random times with variable frequency. Even when they are observed, they may be disregarded because they are considered “abnormal.” Work sampling methods can be used to study these variations, but they required many observations over days and weeks and even seasons to evaluate rigorously. We propose to use computer and laboratory simulations to build and evaluate models that then can be evaluated using filed studies for use by safety and health professionals and work designers to avoid work conditions associated with WMSDs.

A computer model has been proposed and tested using simulation. Three laboratory experiments are proposed to test the hypothesis that risk factors are related to: (1) product mix and sequence, (2) interarrival time, and (3) target size of assemblies. We have constructed a virtual assembly line that can be used to create the proposed test conditions. The hardware and software enables us to control the force requirements, track hand motions and integrate them into the virtual assembly line. Selected postuure data are collected using an Optotrak Certus® motion capture system. The product mix and sequence experiment has started, but we have been able to test only three subjects. This work demonstrates the feasibility of this research, but additional resources are for subjects and assistance to complete the data collection and analysis.