Histopathology and production of repair proteins in flexor digitorum tendons and muscles after performance of either a LRLF, HRLF, LRHF and HRHF task for 12 weeks. (A) Representative photos of ED1-immunoreactive (ED1-IH) macrophages in muscles (M) in a normal control rat and a 12-week HRHF rat. Arrows indicate ED1-IH macrophages; the arrow with the asterisk indicates a myofiber that is smaller than the others and that contains an ED1-IH cell within the myofiber, both indicative of a degenerating myofiber. Eosin counterstain (pink) shows increased collagen matrix between myofibers, indicative of fibrosis. (B) Inducible heat shock protein 72 (HSP72) in muscles. (C) Combined tendon pathology scores for cellularity, cell shape, and collagen organization (Bonar scoring system used in which 12 is the total score). (D) HSP72 in tendons. (E) Transforming growth factor beta 1 (TGFB1) in tendons. (F) Representative photos of H&E stained tendons showing elongated tenocytes and parallel collagen fibrils in a normal control endotendon, but rounded cells (tenocytes but also likely to include macrophages) and disrupted collagen fibrils in a 12-week HRHF endotendon. Symbols: aa: p < 0.01, compared to LRLF rats; bb: p < 0.01, compared to HRLF rats; **: p < 0.01, compared to normal controls (NC) rats (indicated by dashed line). Mean and SEM are shown. Scale bars = 50 micrometers.