Elastic properties of tendon measured by two different approaches

Elastic properties of tendon were assessed by two different approaches. Six fresh bovine Achilles tendon specimens were used. The first approach direc tly measured Young's modulus along the transverse direction (E-perpendicula r) and the longitudinal direction (E-parallel), using a cyclic compression- relaxation method. Young's moduli were derived based on the measured strain and stress values. The ratio of E-parallel: E-perpendicular at smaller str ains was around 4 and decreased to 0.6 similar to1.1 at larger strains. The second approach assumed that tendons are transversely isotropic. Three obs ervable second-order elastic stiffness constants (c(11), C-13 and C-33) wer e obtained by sound speed measurements along various propagation directions . The measured elastic stiffness constants were also correlated with result s from the first approach. It was shown that the transverse isotropy assump tion was valid at small strains. However, a significant discrepancy existed between the two approaches. The discrepancy was primarily due to viscoelas ticity associated with the first approach.