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Effect of repetition or force in aged rats with WMSD.

Barbe MF; Barr AE; Clark B; Safadi FF
Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health,U01-OH-008599, 2008 Sep; :1-13
Work-related musculoskeletal disorders (WMSD) account for one in three lost work time illnesses. The mechanisms of pathophysiology are incompletely understood. Animal models provide an opportunity to examine the effects of these tasks on tissues under controlled experimental conditions. In the past, we explored the effect of repetitive and/or forceful reaching and grasping in young adult rats. In this 3-year study, we extended our model to consider the effects of aging. Aim I: To determine the extent to which exposure to two task regimens, high repetition-low force (HRLF) and low repetition-low force (LRLF) causes tissue injury, inflammation, fibrosis and degeneration in musculoskeletal and neural tissues of the upper extremity in aged rats. Aim II: To determine the extent to which exposure to the two task regimens (HRLF. LRLF) causes declines in motor performance in aged rats. Aim III. To determine the extent to which the two tasks cause psychosocial behavior dysfunction in aged rats. The aged rats were 15 months of age at the time of task onset. We found that the HRLF task produced upper extremity musculoskeletal and nerve tissue damage, inflammation and sensorimotor declines, but that the LFLF task did not. Thus, we added young rats performing the HRLF task to the project for comparison purposes. We found that the HRLF task produced earlier tissue damage, and greater levels of local and systemic inflammation in aged than in young rats. The damage to bone and nerve was more pronounced in aged than in young rats and did not show recovery. Several proteins related to mechanisms of repair were down regulated in aged rats compared to young rats. Functionally, palmar skin hypersensitivity was observed almost immediately after onset of task performance. This hypersensitivity matched observed degradation of nerve endings in palmar skin. With continued performance or the HRLF task for 3 months, significant declines in median nerve conduction velocity was present bilaterally in aged rats. Progressive declines in grip strength and social interaction abilities were also evident almost immediately after onset of HRLF task performance in aged rats, as was increased aggression. The psychosocial behavioral declines resembled "sickness behaviors" and correlated highly with increased serum levels of pro-inflammatory cytokines and chemokines. In conclusion, we found that the tissue pathophysiology in WMSD is inflammatory in nature initially. A local and systemic inflammatory response appears to induce nerve fibrosis and significant declines in bone formation with continued task performance. These changes were amplified in aged rats compared to young rats. These findings have considerable importance to those designing effective prevention and management plans in older adults with WMSDs.
Musculoskeletal-system; Musculoskeletal-system-disorders; Workers; Animals; Laboratory-animals; Repetitive-work; Force; Models; Age-factors; Exposure-levels; Tissue-culture; Injuries; Fibrosis; Psychological-factors; Behavior; Nerve-damage; Nerve-tissue; Sociological-factors
Mary F. Barbe, 3307 North Broad Street, Temple University, Philadelphia, PA 19140
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Final Cooperative Agreement Report
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Cooperative Agreement
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NIOSH Division
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National Institute for Occupational Safety and Health
Performing Organization
Temple University, Philadelphia, Pennsylvania
Page last reviewed: March 25, 2022
Content source: National Institute for Occupational Safety and Health Education and Information Division