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.

No abstract

This investigation presents a new approach in the measurement of the mechanical properties of the ligament substance from tensile testing of a bone-ligament-bone complex. Such basic information should be one of the necessary prerequisites in the evaluation of ligament repair as well as reconstruction by autogenous tissue grafts or artificial ligament implants. The use of a video system permits the determination of tensile strains of the mid-medial collateral ligaments from the canine, swine, and rabbit without mechanically interfering with the ligament deformation during testing. This methodology further eliminates the difficulties of measuring the initial length of the entire medial collateral ligament, as its insertions to bones are ambiguous and cover a large area. It was found that the strain of the ligament substance is consistently and considerably less than specific deformation of the bone-ligament-bone complex. These data suggest that the ligament-bone structure stretches nonuniformly with the highest deformation occurring near or at the ligament insertion sites to bone. Other interesting findings include the variation of tensile strains along the ligament substance for all animal species studied.

The digital flexor tendons of the miniature swine were studied after 12 mo of running exercise. Using a newly developed methodology whereby the properties of tendon substance and tendon-bone composite are measured simultaneously, it was found that training augments the strength of the tendon insertion site, but has minimal effect on the tendon substance. Biochemical analyses also showed that the collagen concentration in the tendon substance remains unchanged following exercise. There was also moderate, but not significant, tendon hypertrophy. The present results on flexor tendon differ from those previously obtained for the swine digital extensors [6]. Such difference in response to functional stress may be attributed to the biochemical composition and mechanical properties of these tissues.

The viscoelastic properties of the canine medial collateral ligament (MCL) were investigated. Stress-strain relationships at different strain rates, long-term stress relaxation and cyclic stress-strain curves of the MCL were obtained experimentally using a bone-MCL-bone preparation. The experimental data were used in conjunction with the quasi-linear viscoelastic theory as proposed by Fung [15] to characterize the reduced relaxation function, G(t) and elastic response sigma e (epsilon) of this tissue. It was found that the quasi-linear viscoelastic theory can adequately describe the time and history-dependent rheological properties of the canine medial collateral ligament.