Effect of tendon stiffness on the generated force at the Achilles tendon - 3D finite element simulation of a human triceps surae muscle during isometric contraction

Abstract

Skeletal muscles develop forces as a result of muscle activation for human locomotion. To know the force generating ability of skeletal muscles is important to understand the muscle functions. Computer simulation is a useful tool for estimating the force generating ability. Therefore we have developed a three-dimensional (3D) finite element software to simulate both the so-called passive behavior of biological soft tissues and the muscle active behavior. The software is based on a nonlinear finite element setting for almost incompressible hyperelastic materials, where a total Lagrangian formulation, a mixed type displacement-pressure finite element and a fully implicit time integration scheme are adopted. The active stress as a result of muscle contraction is modeled by Hill-type model. Here, we investigated the effect of tendon stiffness within the range indicated in several literatures on the generated force at the Achilles tendon during isometric contraction of the triceps surae muscle. 3D FE-model of a human triceps surae muscle reconstructed by magnetic resonance images, which have the 3D distribution of the fascicle arrangement within the muscles. The stiffer tendon generated higher force at the Achilles tendon than the low-stiffness tendon, and the largest generated force was 1.45 times greater than the smallest one. It is, therefore, important to carefully obtain the material parameters from in vivo experimental observations. In this software, the subject-specific geometry and material properties can be used in the simulation. This software may therefore become a valuable tool for studying on orthopedics and rehabilitation planning, as well as for improving our understanding of muscle mechanics.

Keywords

• finite element method
• muscle contraction
• tendon stiffness
• triceps surae muscle
• achilles tendon force