Positive effects on the tensile characteristics of swine digital extensors were found following twelve months of exercise training. Compared to sedentary controls, the tendons from the exercised animals became stronger as a material and exhibited hypertrophy. These biomechanical results were supported by biochemical analyses of tendon composition. Exercise increased the concentration of collagen as well as the total weights of the tendons. For determining stress and strain in tendon material, we used specially designed instruments to measure the tendon cross-sectional area, and a video dimensional analyzer system to measure accurately its "non-contact" tensile strain. With these newly developed apparatus, the mechanical properties of the tendons were accurately determined so that the effects of exercise training could be compared.