title: Exercise protocol induces muscle, tendon, and bone adaptations in the rat shoulder.
abstract: BACKGROUND
  a rat model of supraspinatus overuse has suggested mechanisms governing tendon degeneration; however, delineating which changes are pathologic or simply physiologic adaptations to increased loading remains a question. The objective of this study was to develop and characterize a rat exercise model that induces systemic and local shoulder adaptations without mechanical injury to the supraspinatus tendon.
  
  
  METHODS
  exercise rats completed a treadmill training protocol for 12 weeks. Body, fat pad, and heart weights were determined. Supraspinatus tendon collagen content, cross-sectional area, and mechanical properties were measured. Supraspinatus muscle cross-sectional area, weight, and the expression of mitochondrial oxidative phosphorylation (OXPHOS) proteins were measured. Humeri were analyzed with μCT and mechanically tested.
  
  
  RESULTS
  exercise decreased fat pad mass. Supraspinatus muscle hypertrophied and had increased OXPHOS proteins. Humerus trabecular bone had increased anisotropic orientation, and cortical bone showed increased bone and tissue mineral density. Importantly, the supraspinatus tendon did not have diminished mechanical properties, indicating that this protocol was not injurious to the tendon.
  
  
  CONCLUSIONS
  this study establishes the first rat exercise protocol that induces adaptations in the shoulder. Future research can use this as a comparison model to study how the supraspinatus tendon adapts to loading and undergoes degeneration with overuse.
authors.affiliation: McKay Orthopaedic Research Lab, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Sarah Ilkhanipour
authors.initials: SI
authors.lastname: Rooney
authors.affiliation: Department of Physiology, Pennsylvania Muscle Institute, University of Pennsylvania School of Medicine, Philadelphia, PA, USA.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Loro
authors.affiliation: Biomedical Engineering, Drexel University, Philadelphia, PA, USA; McKay Orthopaedic Research Lab, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Sarver
authors.affiliation: Bone & Joint Center, Henry Ford Hospital, Detroit, MI, USA; McKay Orthopaedic Research Lab, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Cathryn D
authors.initials: CD
authors.lastname: Peltz
authors.affiliation: McKay Orthopaedic Research Lab, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Hast
authors.affiliation: McKay Orthopaedic Research Lab, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Wei-Ju
authors.initials: WJ
authors.lastname: Tseng
authors.affiliation: McKay Orthopaedic Research Lab, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Andrew F
authors.initials: AF
authors.lastname: Kuntz
authors.affiliation: McKay Orthopaedic Research Lab, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: X Sherry
authors.initials: XS
authors.lastname: Liu
authors.affiliation: Department of Physiology, Pennsylvania Muscle Institute, University of Pennsylvania School of Medicine, Philadelphia, PA, USA.
authors.forename: Tejvir S
authors.initials: TS
authors.lastname: Khurana
authors.affiliation: McKay Orthopaedic Research Lab, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Louis J
authors.initials: LJ
authors.lastname: Soslowsky
keywords: mechanics; rotator cuff; supraspinatus; tendinopathy