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Performance of Repetitive Tasks Induces Decreased Grip Strength and Increased Fibrogenic Proteins in Skeletal Muscle: Role of Force and Inflammation

  • Abdelmagid, Samir M. (Department of Surgery, Plastic and Reconstructive Division, Children's Hospital of Philadelphia)
  • Barr, Ann E. (Pacific University)
  • Rico, Mario (Sol Sherry Thrombosis Research Center, Temple University School of Medicine)
  • Amin, Mamta (Department of Anatomy and Cell Biology, Temple University School of Medicine)
  • Litvin, Judith (Department of Anatomy and Cell Biology/Musculoskeletal Research Group, Temple University School of Medicine)
  • Popoff, Steven N. (Department of Anatomy and Cell Biology/Musculoskeletal Research Group, Temple University School of Medicine)
  • Safadi, Fayez F. (Musculoskeletal Research Group, Temple University School of Medicine & Department of Anatomy and Neurobiology, Northeast Ohio Medical University)
  • Barbe, Mary F. (Department of Anatomy and Cell Biology/Musculoskeletal Research Group, Temple University School of Medicine)
1 January 2012



This study elucidates exposure-response relationships between performance of repetitive tasks, grip strength declines, and fibrogenic-related protein changes in muscles, and their link to inflammation. Specifically, we examined forearm flexor digitorum muscles for changes in connective tissue growth factor (CTGF; a matrix protein associated with fibrosis), collagen type I (Col1; a matrix component), and transforming growth factor beta 1 (TGFB1; an upstream modulator of CTGF and collagen), in rats performing one of two repetitive tasks, with or without anti-inflammatory drugs.


To examine the roles of force versus repetition, rats performed either a high repetition negligible force food retrieval task (HRNF), or a high repetition high force handle-pulling task (HRHF), for up to 9 weeks, with results compared to trained only (TR-NF or TR-HF) and normal control rats. Grip strength declined with both tasks, with the greatest declines in 9-week HRHF rats. Quantitative PCR (qPCR) analyses of HRNF muscles showed increased expression of Col1 in weeks 3–9, and CTGF in weeks 6 and 9. Immunohistochemistry confirmed PCR results, and also showed greater increases of CTGF and collagen matrix in 9-week HRHF rats than 9-week HRNF rats. ELISA, and immunohistochemistry revealed greater increases of TGFB1 in TR-HF and 6-week HRHF, compared to 6-week HRNF rats. To examine the role of inflammation, results from 6-week HRHF rats were compared to rats receiving ibuprofen or anti-TNF-α treatment in HRHF weeks 4–6. Both treatments attenuated HRHF-induced increases in CTGF and fibrosis by 6 weeks of task performance. Ibuprofen attenuated TGFB1 increases and grip strength declines, matching our prior results with anti-TNFα.


Performance of highly repetitive tasks was associated with force-dependent declines in grip strength and increased fibrogenic-related proteins in flexor digitorum muscles. These changes were attenuated, at least short-term, by anti-inflammatory treatments.


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