How muscle stiffness affects human body model behavior

Area of Science:

• Biomechanics and Computational Modeling
• Finite Element Analysis in Automotive Safety

Background:

• Active Human Body Models (AHBM) utilize 1D truss elements for muscles, but simplified volumetric muscle models based on Post Mortem Human Subject (PMHS) data are less developed.
• The impact of isometric contraction-induced stiffness changes in volumetric muscles on AHBM behavior and computational cost remains largely unexplored.

Purpose of the Study:

• To investigate the effect of varying volumetric muscle stiffness on the dynamic response of an Active Human Body Model (AHBM) during frontal impact simulations.
• To assess the influence of these stiffness changes on computational time and injury outcomes.

Main Methods:

• Simulated a simplified frontal impact scenario using the THUMS Version 5 AM50 occupant model.
• Modified the material model (MAT_SIMPLIFIED_FOAM) parameters to define different stiffness states for volumetric muscles in the buttock and thigh regions.

Main Results:

• Changes in muscle stiffness significantly influenced the overall AHBM behavior and predicted injury outcomes during frontal crashes.
• Altering muscle stiffness in the thigh, pelvis, or the entire model, including strain-rate-dependent definitions, did not significantly affect computation time.

Conclusions:

• Modifying THUMS material model parameters provides an efficient method to adjust volumetric muscle stiffness in AHBM for dynamic applications without increasing computation time.
• While results show compliance with literature, validation is limited due to a lack of specific experimental data for automotive frontal impacts. Future work should explore advanced material models for improved biofidelity.