Age-related changes in biomechanical properties of the Achilles tendon in rabbits

We investigated age-related changes in the mechanical properties of rabbit Achilles tendon. The animals used were immature (age 3 weeks, body mass 380 g), young adult (age 8–10 months, body mass 4.1 kg) and old (age 4–5 years, body mass 5.1 kg) rabbits. The cross-sectional area of the tendon increased with growth and the tensile strength of the young adult [67.3 (SEM 4.2) MPa] and old [66.7 (SEM 3.8) MPa] tendon was significantly higher than that of the immature tendon [23.9 (SEM 3.8) MPa]. However, there was no statistically significant difference in tensile strength between mature and old tendons. These differences may be attributable to the change in body mass. The gradient of the stress-strain curves, that is, the tangent modulus of the mature tendon [618.0 (SEM 87.0) MPa], was higher than that of the immature [281.0 (SEM 104.6) MPa] and old [530.5 (SEM 91.0) MPa] tendon, although the difference was not significant. The elongation at failure was approximately 16% for all age groups. These results would suggest that rabbit Achilles tendon is highly compliant during growth.