Augmented Soft Tissue Mobilization, a massage therapy which uses a solid instrument rather than human fingers to treat musculoskeletal injuries, has been successful in treating tendinitis. Davidson et al. studied the functional and morphological affects of ASTM on collagenase induced Achilles tendinitis in Sprague-Dawley rats. Morphological observations showed a significant increase in the number and activation of fibroblasts in the ASTM treated Groups. The authors suggested that the physical force of ASTM may promote tendon healing via increased fibroblast recruitment. An important, but unexplained, question is how ASTM would affect the fibroblasts of native, noncollagenase injured, tendons. Studies have shown that mechanical forces can alter cellular functions. The purpose of this study was to examine the morphological changes in native Sprague-Dawley rat Achilles tendons after ASTM therapy using different application pressures.Three animal Groups were randomly established: A) control Group with no ASTM; B) light ASTM with 1 Newton of pressure; and C) heavy ASTM with 3 Newtons of pressure. Upon completion of the therapy, the Achilles tendons of each Group were examined with light and electron microscopy techniques to assess fibroblast number, tendon morphology, and the presence of type I and type III collagen. Fibroblast counts from each Group were compared using a two-way ANOVA, multiple regression, and curvilinear regression analysis. Morphological differences were shown between the three Groups, especially between the non force Group and the two force Groups. The ASTM Group treated with one Newton demonstrated the greatest mean fibroblast count (165.1+/-55.8&160.7+/-49.8). Electron microscopy revealed the presence of activated fibroblasts in the tendons of the two force Groups, ASTM Groups. Polarizing microscopy showed a dramatic increase in the amount of Type III collagen in the two force Groups compared to the non force Group.Ball State UniversityMuncie, IN 47306