A validated model of passive muscle in compression

Area of Science:

• Biomechanics
• Materials Science
• Computational Modeling

Background:

• Accurate characterization of soft tissues is essential for enhancing human body models.
• Current models often lack precision in representing complex tissue behaviors, impacting applications like virtual crash modeling.

Purpose of the Study:

• To develop and validate a theoretical model for characterizing the quasi-static, 3D compressive behavior of skeletal muscle.
• To compare the predictive capabilities of a transversely isotropic hyperelastic model against a strain-dependent Young's moduli (SYM) model.

Main Methods:

• Conducted uniaxial, unconstrained compression experiments on fresh and aged animal muscle samples.
• Oriented samples at various angles relative to the muscle fiber direction.
• Fitted experimental data to a transversely isotropic hyperelastic model and the SYM model.

Main Results:

• The hyperelastic model showed limitations in fitting data across all testing directions.
• The SYM model provided a good fit to experimental data in fiber, cross-fiber, and 45-degree directions up to 30% strain for aged samples.
• The SYM model effectively captured differences in behavior between fresh and aged tissues and predicted behavior at 30 and 60 degrees from the fiber direction.

Conclusions:

• The strain-dependent Young's moduli (SYM) model offers superior accuracy in predicting skeletal muscle's quasi-static compressive behavior compared to the hyperelastic model.
• The SYM model's ability to account for fiber direction and tissue age is critical for realistic human body modeling.
• Significant stiffening of muscle tissue occurs within hours post-mortem, a factor that must be considered in experimental characterization.