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Neck Muscle Load Distribution in Lateral, Frontal, and Rear-end Impacts: A Three-Dimensional Finite Element Analysis
KTH, School of Technology and Health (STH), Neuronic Engineering.
KTH, School of Technology and Health (STH), Neuronic Engineering.
MEA Forensic Engineers and Scientists Ltd., Richmond, BC, Canada.
2009 (English)In: Spine, ISSN 0362-2436, E-ISSN 1528-1159, Vol. 34, no 24, 2626-2633 p.Article in journal (Refereed) Published
Abstract [en]

Study Design. A finite element (FE) model of the human neck was used to study the distribution of neck muscle loads during multidirectional impacts. The computed load distributions were compared to experimental electromyography (EMG) recordings.

Objective. To quantify passive muscle loads in nonactive cervical muscles during impacts of varying direction and energy, using a three-dimensional (3D) continuum FE muscle model.

Summary of Background Data. Experimental and numerical studies have confirmed the importance of muscles in the impact response of the neck. Although EMG has been used to measure the relative activity levels in neck muscles during impact tests, this technique has not been able to measure all neck muscles and cannot directly quantify the force distribution between the muscles. A numerical model can give additional insight into muscle loading during impact.

Methods. An FE model with solid element musculature was used to simulate frontal, lateral, and rear-end vehicle impacts at 4 peak accelerations. The peak cross-sectional forces, internal energies, and effective strains were calculated for each muscle and impact configuration. The computed load distribution was compared with experimental EMG data.

Results. The load distribution in the cervical muscles varied with load direction. Peak sectional forces, internal energies, and strains increased in most muscles with increasing impact acceleration. The dominant muscles identified by the model for each direction were splenius capitis, levator scapulae, and sternocleidomastoid in lateral impacts, splenius capitis, and trapezoid in frontal impacts, and sternocleidomastoid, rectus capitis posterior minor, and hyoids in rear-end impacts. This corresponded with the most active muscles identified by EMG recordings, although within these muscles the distribution of forces and EMG levels were not the same.

Conclusion. The passive muscle forces, strains, and energies computed using a continuum FE model of the cervical musculature distinguished between impact directions and peak accelerations, and on the basis of prior studies, isolated the most important muscles for each direction.

Place, publisher, year, edition, pages
2009. Vol. 34, no 24, 2626-2633 p.
Keyword [en]
Finite Element, cervical musculature, impact biomechanics, muscle load, EMG
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-9499DOI: 10.1097/BRS.0b013e3181b46bddISI: 000271884700005ScopusID: 2-s2.0-72849123527OAI: diva2:114236
QC 20100809. Uppdaterad från submitted till published (20100809). Tidigare titel: Neck Muscle Load Distribution in Lateral, Frontal, and Rear-end Impacts: a 3D Finite Element AnalysisAvailable from: 2008-11-10 Created: 2008-11-10 Last updated: 2010-08-09Bibliographically approved
In thesis
1. 3D Finite Element Modeling of Cervical Musculature and its Effect on Neck Injury Prevention
Open this publication in new window or tab >>3D Finite Element Modeling of Cervical Musculature and its Effect on Neck Injury Prevention
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Injuries to the head and neck are potentially the most severe injuries in humans, since they may damage the nervous system. In accidents, the cervical musculature stabilizes the neck in order to prevent injury to the spinal column and is also a potential site for acute muscle strain, resulting in neck pain. The musculature is consequently an important factor in the understanding of neck injuries. There is however a lack of data on muscle response and little is known about the dynamics of the individual muscles. In this thesis the numerical method of Finite Elements (FE) is used to examine the importance of musculature in accidental injuries. In order to study the influence of a continuum musculature, a 3D solid element muscle model with continuum mechanical material properties was developed. It was hypothesized that a 3D musculature model would improve the biofidelity of a numerical neck model by accounting for the passive compressive stiffness, mass inertia, and contact interfaces between muscles. A solid element representation would also enable the study of muscle tissue strain injuries.

A solid element muscle model representing a 50th percentile male was created, based on the geometry from MRI, and incorporated into an existing FE model of the spine. The passive material response was modeled with nonlinear-elastic and viscoelastic properties derived from experimental tensile tests. The active forces were modeled with discrete Hill elements. In the first version of the model the passive solid element muscles were used together with separate active spring elements. In the second version the active elements were integrated in the solid mesh with coincident nodes. This combined element, called the Super-positioned Muscle Finite Element (SMFE), was evaluated for a single muscle model before it was incorporated in the more complex neck muscle model. The main limitation of the SMFE was that the serial connected Hill-type elements are unstable due to their individual force-length relationship. The instabilities in the SMFE were minimized by the addition of passive compressive stiffness from the solid element and by the decreased gradient of the force-length relation curve.

 The solid element musculature stabilized the vertebral column and reduced the predicted ligament strains during simulated impacts. The solid element compressive stiffness added to the passive stiffness of the cervical model. This decreased the need for additional active forces to reproduce the kinematic response of volunteers during impact. The active response of the SMFE improved model biofidelity and reduced buckling of muscles in compression. The solid element model predicted forces, strains, and energies for individual muscles and showed that the muscle response is dependent on impact direction and severity. For each impact direction, the model identified a few muscles as main load carriers that corresponded to muscles generating high EMG signals in volunteers. The single largest contributing factor to neck injury prediction was the muscle active forces. Muscle activation reduced the risk of injury in ligaments in high-energy impacts. The most urgent improvements of the solid element muscle model concerns: the stability of the SMFE; the boundary conditions from surrounding tissues; and more detailed representations of the myotendinous junctions. The model should also be more extensively validated for the kinematical response and for the muscle load predictions.

It was concluded that a solid muscle model with continuum mechanical material properties improves the kinematical response and injury prediction of a FE neck model compared to a spring muscle model. The solid muscle model can predict muscle loads and provide insight to how muscle dynamics affect spinal stability as well as muscle acute strain injuries.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. vii, 60 p.
Trita-STH : report, ISSN 1653-3836 ; 2008:6
Finite Element, Cervical Musculature, Neck injury prediction, Continuum Mechanics, Solid Elements
National Category
Engineering and Technology
urn:nbn:se:kth:diva-9503 (URN)978-91-7415-180-0 (ISBN)
Public defence
2008-12-05, 3-221, Alfred Nobels Allé 10, Huddinge, 13:00 (English)
QC 20100809Available from: 2008-11-17 Created: 2008-11-10 Last updated: 2010-08-09Bibliographically approved

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