Development and verification of a physiologically motivated internal controller for the open-source extended Hill-type muscle model in LS-DYNA

Abstract

Nowadays, active human body models are becoming essential tools for the development of integrated occupant safety systems. However, their broad application in industry and research is limited due to the complexity of incorporated muscle controllers, the long simulation runtime, and the non-regular use of physiological motor control approaches. The purpose of this study is to address the challenges in all indicated directions by implementing a muscle controller with several physiologically inspired control strategies into an open-source extended Hill-type muscle model formulated as LS-DYNA user-defined umat41 subroutine written in the Fortran programming language. This results in increased usability, runtime performance and physiological accuracy compared to the standard muscle material existing in LS-DYNA. The proposed controller code is verified with extensive experimental data that include findings for arm muscles, the cervical spine region, and the whole body. Selected verification experiments cover three different muscle activation situations: (1) passive state, (2) open-loop and closed-loop muscle activation, and (3) reflexive behaviour. Two whole body finite element models, the 50th percentile female VIVA OpenHBM and the 50th percentile male THUMS v5, are used for simulations, complemented by the simplified arm model extracted from the 50th percentile male THUMS v3. The obtained results are evaluated additionally with the CORrelation and Analysis methodology and the mean squared error method, showing good to excellent biofidelity and sufficient agreement with the experimental data. It was shown additionally how the integrated controller allows simplified mimicking of the movements for similar musculoskeletal models using the parameters transfer method. Furthermore, the Hill-type muscle model presented in this paper shows better kinematic behaviour even in the passive case compared to the existing one in LS-DYNA due to its improved damping and elastic properties. These findings provide a solid evidence base motivating the application of the enhanced muscle material with the internal controller in future studies with Active Human Body Models under different loading conditions.

Using muscle-tendon load limits to assess unphysiological musculoskeletal model deformation and Hill-type muscle parameter choice

“…Additionally, it consists of distinct muscle and tendon sections, which can be individually evaluated for injury with the MSIC and the TSIC. This Hill-type muscle material was initially implemented in LS-DYNA as the so-called extended Hill-type muscle (EHTM) material model by Kleinbach et al [54] and has since been updated by Wochner et al [55] and Martynenko et al [56]. In our current study, the functionality of the EHTM was further expanded by adding an inbuilt strain injury assessment functionality using the MSIC and TSIC.…”

“…The FE repositioning simulation was performed using the THUMS AM50 occupant model version 5.03 [44]. Seat, steering wheel and pedals were taken from the openly available THUMS version [55] and Martynenko et al [56]. In our current study, the functionality of the EHTM was further expanded by adding an inbuilt strain injury assessment functionality using the MSIC and TSIC.…”

“…To illustrate our proposed method, the previously outlined modelling issues were recreated using [55] and Martynenko et al [56]. In our current study, the functionality of the EHTM was further expanded by adding an inbuilt strain injury assessment functionality using the MSIC and TSIC.…”

An investigation of tendon strains in jersey finger injury load cases using a finite element neuromuscular human body model

“…To allow for a better assessment of tendon strain injury severity, *MAT_MUSCLE was replaced with a more biophysiological Hill-type muscle material developed by ( Günther et al, 2007 ) and Haeufle et al ( Haeufle et al, 2014 ), which is available in LS-DYNA as a user-defined material named the extended Hill-type material (EHTM). The EHTM was initially implemented in LS-DYNA by Kleinbach et al ( Kleinbach et al, 2017 ) and updated to its most current version by Kleinbach et al ( Kleinbach, 2019 ), Martynenko et al ( Martynenko et al, 2023 ) and Wochner et al ( Wochner et al, 2022 ). Compared to *MAT_MUSCLE, the EHTM material has the additional benefit of including the tendon as a distinct element called the serial elastic element (SEE) ( Haeufle et al, 2014 ), eliminating the need for combining muscle and seatbelt elements to form the MTU.…”