MMP13 and disease of the tendon: We hypothesized that moderate tendinopathy: (1) occurs at a time point between 3 and 6 days SD; and (2) is characterized by a progressive increase in cell apoptosis, cell roundness, and MMP-13 level, a progressive decrease in fiber density, and mechanical properties as well as a reversal of cell density trend, i.e., a decrease following an initial increase.