Key result
VEXAT muscle model outperforms MAT_156 and EHTM in simulating active lengthening and vibration forces.
Why the study?
Digital human body models use muscle models to simulate movement and injury from accidents, but the accuracy of different LS-DYNA muscle models across varying experimental conditions required evaluation.
The VEXAT muscle model in LS-DYNA provides superior accuracy over MAT_156 and EHTM in simulating active lengthening and vibration due to the inclusion of viscoelastic cross-bridges and an active titin filament.
Supports refined biomechanical muscle modeling; leaves open human validation before clinical use.
Digital human body models are used to simulate injuries that occur as a result of vehicle collisions, vibration, sports, and falls. Given enough time the body's musculature can generate force, affect the body's movements, and change the risk of some injuries. The finite-element code LS-DYNA is often used to simulate the movements and injuries sustained by the digital human body models as a result of an accident. In this work, we evaluate the accuracy of the three muscle models in LS-DYNA (MAT_156, EHTM, and the VEXAT) when simulating a range of experiments performed on isolated muscle: force-length-velocity experiments on maximally and sub-maximally stimulated muscle, active-lengthening experiments, and vibration experiments. The force-length-velocity experiments are included because these conditions are typical of the muscle activity that precedes an accident, while the active-lengthening and vibration experiments mimic conditions that can cause injury. The three models perform similarly during the maximally and sub-maximally activated force-length-velocity experiments, but noticeably differ in response to the active-lengthening and vibration experiments. The VEXAT model is able to generate the enhanced forces of biological muscle during active lengthening, while both the MAT_156 and EHTM produce too little force. In response to vibration, the stiffness and damping of the VEXAT model closely follows the experimental data while the MAT_156 and EHTM models differ substantially. The accuracy of the VEXAT model comes from two additional mechanical structures that are missing in the MAT_156 and EHTM models: viscoelastic cross-bridges, and an active titin filament. To help others build on our work we have made our simulation code publicly available.
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Millard et al. (2024) studied Muscle modeling. VEXAT muscle model vs. MAT_156 and EHTM muscle models was evaluated on Accuracy in simulating force-length-velocity, active-lengthening, and vibration experiments on isolated muscle. The VEXAT muscle model accurately simulated enhanced forces during active lengthening and stiffness/damping during vibration, outperforming the MAT_156 and EHTM models.
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