Laboratory rats reaching repetitively for food have shown signs similar to work-related musculoskeletal disorders (MSDs) seen in humans, according to a new study partly funded by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS). The rodents had tissue injuries, inflammation and reduced motor performance after voluntarily reaching for and grasping food over an eight-week period.

Mary F. Barbe, M.D., Ann E. Barr, P.T., Ph.D., and colleagues at Temple University measured changes in motor skills and tissues in 39 female rats trained to perform highly repetitive reaching and grasping tasks. The animals performed the tasks, which mimicked some characteristics of human job-related movements, for 2 hours a day 3 days a week over the study period. Tissue samples were collected and proteins related to inflammatory response were isolated from reaching and nonreaching forelimbs. The researchers found that the tissue changes and behavioral responses of the rats resembled those of humans reporting MSDs. Specifically, the scientists saw a gradual decline in how often the animals reached for food and in how long they would continue to reach. Form and structure changes were seen in muscle tissues, as were increased immune and inflammatory responses.

Work-related MSDs can result from such ergonomic risk factors as repetition, force and awkward or static positioning. Study scientists reported that in 2000, an estimated $2 billion was spent on workers’ compensation costs for MSDs. Additional costs, they said, were associated with lost wages and productivity arising from work absences and limited duty.

The study was also supported by the Centers for Disease Control and Prevention and the Foundation for Physical Therapy. The NIAMS is a part of the Department of Health and Human Services’ National Institutes of Health.


Barbe MF, Barr AE, Gorzelany I, Amin M, Gaughan JP, Safadi FF. Chronic repetitive reaching and grasping results in decreased motor performance and widespread tissue responses in a rat model of MSD. J Orthopaedic Res 2003; 21:167-176.

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