For the purpose of determining the changes in tensile strength and levels of macromolecular orientation in collagen bundles as a result of mechanical stimuli, rats were submitted to different experimental treatments such as physical exercise and muscular denervation. After these treatments the Achilles tendons of the animals were submitted to biomechanical and biophysical testing. An analysis of the "stress"-strain curves indicated that the tendons of trained animals possessed superior tensile strength characteristics as compared to their controls. The form birefringence curves (FBC) of the collagen bundles in these tendons also showed an increase in their state of aggregation of the extracellular matrix elements, while maintaining their levels of crystallinity. Average values of tensile strength were even higher in the tendons of denervated animals. An accentuation of the profile of the FBC was also observed in these tendons. The determination of the biomechanical and biophysical modifications can contribute to the understanding of the probable control mechanisms of the aggregation state patterns of the fibrous elements of the extracellular matrix.