A benchmark of muscle models to length changes great and small

• Published in: Journal of the mechanical behavior of biomedical materials 2024-12, Vol.160, p.106740, Article 106740
• Main Authors: Millard, Matthew, Stutzig, Norman, Fehr, Jörg, Siebert, Tobias
• Format: Article
• Language: English
• Subjects: Active lengthening; Benchmark; Benchmarking; Biomechanical Phenomena; Finite Element Analysis; Force–length relation; Force–velocity relation; Humans; Impedance; LS-DYNA; Mechanical Phenomena; Models, Biological; Muscle model; Muscle, Skeletal - physiology; Muscles - physiology; Vibration
• ISSN: 1751-6161; 1878-0180; 1878-0180
• DOI: 10.1016/j.jmbbm.2024.106740

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. [Display omitted] •Hill-type muscle models are inaccurate during active lengthening.•The active impedance of Hill-type muscle models is too damped.•In contrast, the VEXAT model’s impedance and active-lengthening response is more accurate.•The VEXAT model is more accurate because of its viscoelastic crossbridge and titin elements.