Ligament and Tendon Enthesis: Anatomy and Mechanics - Structural Interfaces and Attachments in Biology - page 75

Fig. 4.7 Curves summarizing the homeostatic responses of the components of the bone-ligament-
bone complex when it was subjected to different levels of physical activity (reproduced, with
permission, from [ 1 ])

4.4.3 Effects of Exercise

The relationship between physical activity and soft tissue and insertion site properties
has also been shown to have an effect on ligament and tendon entheses. Laboratory
studies have directly addressed the effect of exercise on these tissues, including
some reports on the effects of exercise on tissue biomechanical properties [ 18 - 20 ].
Our research center has performed studies of the biochemical and biomechanical
properties of the isolated swine extensor tendon using 1-year-old swine following a
1-year exercise regime [ 18 ]. A second, sedentary group was used as a control.
Load-deformation curves were produced typical of the characteristic nonlinear
tensile behavior of tendons, beginning with an initial toe region of low stiffness,
where the ligament has not been fully extended, followed by an intermediate
linear region, and finally a yield region as fibers begin to fail and the tendon
ruptures. Exercised medial and lateral tendons were found to have a significantly
higher ultimate strength ðs max Þ and lower ultimate strain ðe max Þ : Contrary to several

previous studies, size and composition of the tendons were shown to be affected by
exercise, as cross-sectional area of exercised tendon was found to be 22% greater
than the sedentary control, tendon weights were significantly higher, and collagen
content was found to be significantly greater in the lateral extensor. Thus, this study
demonstrated a clear increase in mechanical properties in addition to hypertrophy
and increased collagen content of the tendon.
A parallel study using the swine flexor tendon was also done [ 20 ]. Exercise was
found to improve the strength of the flexor tendon, as exercised tendons displayed
an ultimate load and linear load-deformation slope 19 and 26% higher than control