FRITZ, V. K. and W. T. STAUBER. Characterization of muscles injured by forced lengthening. II. Proteoglycans. Med, Sci. Sports Exerc, Vol. 20, No. 4, pp. 354-361, 1988. After forced muscle lengthening of rat soleus muscle, alterations in muscle connective tissues were monitored by fluorescent immunohistochemical methods. Monoclonal antibodies directed against the polysaccharide attachment region of proteoglycans were used to observe changes in localization of 4-sulfated, 6-sulfated, or unsulfated chondroitin sulfate disaccharide units covalently bound to the proteoglycan protein core after injury. Additionally, fluorescein-labeled concanavalin A lectin and polyclonal antiserum to heparan sulfate proteoglycan were also localized in muscle sections during the regenerative process over 5 days after injury. Although proteoglycan localization was absent at or near the site of myofiber damage after injury, some distinct basal lamina remained as a matrix for regenerating myofibers. By the fifth day post-injury, the localization of these matrix components had returned to that seen in uninjured soleus muscles. The physiological significance of these extracellular matrix changes appeared to center on the repair of the torn myofiber and indicate an interdependence between myofibers and the extracellular matrix in this type of regeneration.