Hello, world! VIVA+: A human body model lineup to evaluate sex-differences in crash protection

A fast-modeling framework for personalized human body models based on a single image

Finite element human body models (HBMs) are the primary method for predicting human biological responses in vehicle collisions, especially personalized HBMs that allow accounting for diverse populations. Yet, creating personalized HBMs from a single image is a challenging task. This study addresses this challenge by providing a framework for HBM personalization, starting from a single image used to estimate the subject's skin point cloud, the skeletal point cloud, and the relative positions of the skeletons. Personalized HBMs were created by morphing the baseline HBM accounting skin and skeleton point clouds using a point cloud registration-based mesh morphing method. Using this framework, eight personalized HBMs with various biological characteristics (e.g., sex, height, and weight) were created, with comparable element quality to the baseline HBM. The mean geometric errors of the personalized FEMs generated by the framework are less than 7 mm, which was found to be acceptable based on biomechanical response evaluations conducted in this study.

The I-PREDICT 50th Percentile Male Finite Element Model: Development and Validation of the Torso

Behind Armor Blunt Trauma (BABT) is a phenomenon that occurs when energy is transferred from Personal Protective Equipment (PPE) to the human body and can range from minor to fatal injuries. The current standard to evaluate PPE uses Roma Plastilina No. 1 clay and has a poor correlation to human injuries. To provide a more suitable human surrogate for evaluating risk of injury and functional incapacitation due to BABT, the Incapacitation Prediction for Readiness in Expeditionary Domains: an Integrated Computational Tool (I-PREDICT) has developed a 50th percentile male human body model (HBM) to better understand injury mechanisms in the BABT environment. The model was developed using a hierarchical validation approach including component, regional, and whole torso level tests. Material properties were sourced from literature and I-PREDICT experimental test data, and the model was simulated in 25 different validation cases ranging from component level quasi-static tests to high-rate BABT impacts. The model was stable in all 25 simulations. CORrelation and Analysis (CORA) and BioRank were used to objectively quantify the model response. The average CORA and BioRank across all validation cases were 0.78 ± 0.18 and 0.68 ± 0.27, respectively, indicating 'good' agreement by CORA standards and 'excellent' by BioRank standards. When compared to high-rate BABT experimental impacts on post-mortem human subjects, the I-PREDICT HBM accurately predicted rib fracture probability. The ultimate goal of the I-PREDICT model is to predict injury and functional incapacitation for various in theater military applications. This study highlights the development and validation of the I-PREDICT torso and highlights initial BABT use cases.

Isolated Rib Response and Fracture Prediction for Young Mid-Size Male, Enabled by Population Specific Material Models and Rib Cross-Sectional Geometry

Thorax injury remains a primary contributor to mortality in car crash scenarios. Although human body models can be used to investigate thorax response to impact, isolated rib models have not been able to predict age- and sex-specific force-displacement response and fracture location simultaneously, which is a critical step towards developing human thorax models able to accurately predict injury response. Recent advancements in constitutive models and quantification of age- and sex-specific material properties, cross-sectional area, and cortical bone thickness distribution offer opportunities to improve rib computational models. In the present study, improved cortical and trabecular bone constitutive models populated with age-specific material properties, age- and sex-specific population data on rib cross-sectional area, and cortical bone thickness distribution were implemented into an isolated 6th rib from a contemporary human body model. The enhanced rib model was simulated in anterior-posterior loading for comparison to experimental age- and sex-specific (twenty-three mid-size males, age range of 22- to 57-year-old) population force-displacement response and fracture location. The improved constitutive models, populated with age-specific material properties, proved critical to predict the rib failure force and displacement, while the improved cortical bone thickness distribution and cross-sectional area improved the fracture location prediction. The enhanced young mid-size male 6th rib model was able to predict young mid-size male 6th rib experimental force-displacement response and fracture location (overpredicted the displacement at failure by 35% and underpredicted the force at failure by 8% but within ±1 SD). The results of the present study can be integrated into full body models to potentially improve thorax injury prediction capabilities.

A benchmark of muscle models to length changes great and small

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.

Holistic shape variation of the rib cage in an adult population

Traumatic injuries to the thorax are a common occurrence, and given the disparity in outcomes, injury risk is non-uniformly distributed within the population. Rib cage geometry, in conjunction with well-established biomechanical characteristics, is thought to influence injury tolerance, but quantifiable descriptions of adult rib cage shape as a whole are lacking. Here, we develop an automated pipeline to extract whole rib cage measurements from a large population and produce distributions of these measurements to assess variability in rib cage shape. Ten measurements of whole rib cage shape were collected from 1,719 individuals aged 25-45 years old including angular, linear, areal, and volumetric measures. The resulting pipeline produced measurements with a mean percent difference to manually collected measurements of 1.7% ± 1.6%, and the whole process takes 30 s per scan. Each measurement followed a normal distribution with a maximum absolute skew value of 0.43 and a maximum absolute excess kurtosis value of 0.6. Significant differences were found between the sexes (p < 0.001) in all except angular measures. Multivariate regression revealed that demographic predictors explain 29%-68% of the variance in the data. The angular measurements had the three lowest R2 values and were also the only three to have little correlation with subject stature. Unlike other measures, rib cage height had a negative correlation with BMI. Stature was the dominant demographic factor in predicting rib cage height, coronal area, sagittal area, and volume. Subject weight was the dominant demographic factor for rib cage width, depth, axial area, and angular measurements. Age was minimally important in this cohort of adults from a narrow age range. Individuals of similar height and weight had average rib cage measurements near the regression predictions, but the range of values across all subjects encompassed a large portion of their respective distributions. Our findings characterize the variability in adult rib cage geometry, including the variation within narrow demographic criteria. In future work, these can be integrated into computer aided engineering workflows to assess the influence of whole rib cage shape on the biomechanics of the adult human thorax.

Smoothed particle hydrodynamics implementation to enhance vertebral fracture finite element model in a cervical spine segment under compression

Spinal cord injuries (SCIs) can arise from compression loading when a vertebra fractures and bone fragments are pushed into the spinal canal. Experimental studies have demonstrated the importance of both fracture initiation and post-fracture response in the investigation of vertebral fractures and spinal canal occlusion resulting from compression. Finite element models, such as the Global Human Body Models Consortium (GHBMC) model, focused on predicting the initiation location of fractures using element erosion to model hard tissue fracture. However, the element erosion method resulted in a loss of material and structural support during compression, which limited the ability of the model to predict the post-fracture response. The current study aimed to improve the post-fracture response by combining strain-based element erosion with smoothed particle hydrodynamics (SPH) to preserve the volume of the trabecular bone during compression fracture. The proposed implementation was evaluated using a model comprising two functional spinal units (FSUs) (C5-C6-C7) extracted from the GHBMC 50th percentile male model, and loaded under central compression. The original and enhanced models were compared to experimental force-displacement data and measured occlusion of the spinal canal. The enhanced model with SPH improved the shape and magnitude of the force-displacement response to be in good agreement with the experimental data. In contrast to the original model, the enhanced SPH model demonstrated occlusion on the same order of magnitude as reported in the experiments. The SPH implementation improved the post-fracture response by representing the damaged material post-fracture, providing structural support throughout compression loading and material flow leading to occlusion.

Development of personalizable female and male pedestrian SAFER human body models

OBJECTIVES

Vulnerable road users are globally overrepresented as victims of road traffic injuries. Developing biofidelic male and female pedestrian human body models (HBMs) that represent diverse anthropometries is essential to enhance road safety and propose intervention strategies.

METHODS

In this study, 50th percentile male and female pedestrians of the SAFER HBM were developed via a newly developed image registration-based mesh morphing framework. The performance of the HBMs was evaluated by means of a set of cadaver experiments, involving subjects struck laterally by a generic sedan buck.

RESULTS

In simulated whole-body pedestrian collisions, the personalized HBMs effectively replicate trajectories of the head and lower body regions, as well as head kinematics, in lateral impacts. The results also demonstrate the personalization framework's capacity to generate personalized HBMs with reliable mesh quality, ensuring robust simulations.

CONCLUSIONS

The presented pedestrian HBMs and personalization framework provide robust means to reconstruct and evaluate head impacts in pedestrian-to-vehicle collisions thoroughly and accurately.

Forward dynamics computational modelling of a cyclist fall with the inclusion of protective response using deep learning-based human pose estimation

Single bicycle crashes, i.e., falls and impacts not involving a collision with another road user, are a significantly underestimated road safety problem. The motions and behaviours of falling people, or fall kinematics, are often investigated in the injury biomechanics research field. Understanding the mechanics of a fall can help researchers develop better protective gear and safety measures to reduce the risk of injury. However, little is known about cyclist fall kinematics or dynamics. Therefore, in this study, a video analysis of cyclist falls is performed to investigate common kinematic forms and impact patterns. Furthermore, a pipeline involving deep learning-based human pose estimation and inverse kinematics optimisation is created for extracting human motion from real-world footage of falls to initialise forward dynamics computational human body models. A bracing active response is then optimised for using a genetic algorithm. This is then applied to a case study of a cyclist fall. The kinematic forms characterised in this study can be used to inform initial conditions for computational modelling and injury estimation in cyclist falls. Findings indicate that protective response is an important consideration in fall kinematics and dynamics, and should be included in computational modelling. Furthermore, the novel reconstruction pipeline proposed here can be applied more broadly for traumatic injury biomechanics tasks. The tool developed in this study is available at https://kevgildea.github.io/KinePose/.

Upper cervical spine bone mineral content variations in elderly females

The purpose of the study was to determine the bone mineral densities (BMDs) of the C1 and C2 vertebrae and discuss their implications for autonomous vehicle environments and vulnerable road users. Using quantitated computed tomography (QCT), the BMDs were obtained at eight regions for the C1 vertebra and seven regions for the C2 vertebra. The spine surgeon author outlined the boundaries of each region, and nine elderly female human cadaver specimens were used. The regions were based on potential stabilization locations for fracture fixation. In the C1 vertebra, the BMD was greatest at the anterior tubercle, followed by the posterior tubercle, the posterior arch, and the lateral and anterior lateral masses. In the C2 vertebra, the distal odontoid had the greatest BMD, followed by the spinous process, the C2-lateral mass, the odontoid-body interface, and the anterior inferior aspect of the body. Use of these data in female-specific finite element models may lead to a better understanding of load paths, injuries, mechanisms, and tolerance.

How much does the injury risk between average female and average male anthropometry differ? - A simulation study with open source tools for virtual crash safety assessments

Differences in injury risk between females and males are often reported in field data analysis. The aim of this study was to investigate the differences in kinematics and injury risks between average female and male anthropometry in two exemplary use cases. A simulation study comprising the newly introduced VIVA+ human body models (HBM) was performed for two use cases. The first use case relates to whiplash associated disorders sustained in rear impacts and the second to femur fractures in pedestrians impacted by passenger cars as field data indicates that females have higher injury risk compared to males in these scenarios. Detailed seat models and a generic vehicle exterior were used to simulate crash scenarios close to those currently tested in consumer information tests. In the evaluations with one of the vehicle seats and one car shape the injury risks were equal for both models. However, the risk of the average female HBM for whiplash associated disorders was 1.5 times higher compared to the average male HBM for the rear impacts in the other seat and 10 times higher for proximal femur fractures in the pedestrian impacts for one of the two evaluated vehicle shapes.. Further work is needed to fully understand trends observed in the field and to derive appropriate countermeasures, which can be performed with the open source tools introduced in the current study.

Subaxial Cervical Spine Motion With Different Sizes of Head-supported Mass Under Accelerative Forces

INTRODUCTION

The evolution of military helmet devices has increased the amount of head-supported mass (HSM) worn by warfighters. HSM has important implications for spine biomechanics, and yet, there is a paucity of studies that investigated the effects of differing HSM and accelerative profiles on spine biomechanics. The aim of this study is to investigate the segmental motions in the subaxial cervical spine with different sizes of HSM under Gx accelerative loading.

METHODS

A three-dimensional finite element model of the male head-neck spinal column was used. Three different size military helmets were modeled and incorporated into head-neck model. The models were exercised under Gx accelerative loading by inputting low and high pulses to the cervical vertebra used in the experimental studies. Segmental motions were obtained and normalized with respect to the non-HSM case to quantify the effect of HSM.

RESULTS

Segmental motions increased with an increase in velocity at all segments of the spine. Increasing helmet size resulted in larger motion increases. Angulations ranged from 0.9° to 9.3° at 1.8 m/s and from 1.3° to 10.3° at 2.6 m/s without a helmet. Helmet increased motion between 5% to 74% at 1.8 m/s. At 2.6 m/s, the helmet increased segmental motion anywhere from 10% to 105% in the subaxial cervical spine. The greatest motion was seen at the C5-C6 level, followed by the C6-C7 level.

CONCLUSIONS

The subaxial cervical spine experiences motion increases at all levels at both velocity profiles with increasing HSM. Larger helmet and greater impact velocity increased motion at all levels, with C5-C6 demonstrating the largest range of motion. HSM should be minimized to reduce the risk of cervical spine injury to the warfighter.

Investigating sources for variability in volunteer kinematics in a braking maneuver, a sensitivity analysis with an active human body model

Occupant kinematics during evasive maneuvers, such as crash avoidance braking or steering, varies within the population. Studies have tried to correlate the response to occupant characteristics such as sex, stature, age, and BMI, but these characteristics explain no or very little of the variation. Therefore, hypothesis have been made that the difference in occupant response stems from voluntary behavior. The aim of this study was to investigate the effect from other sources of variability: in neural delay, in passive stiffness of fat, muscle tissues and skin, in muscle size and in spinal alignment, as a first step towards explaining the variability seen among occupants in evasive maneuvers. A sensitivity analysis with simulations of the SAFER Human Body Model in braking was performed, and the displacements from the simulations were compared to those of volunteers. The results suggest that the head and torso kinematics were most sensitive to spinal alignment, followed by muscle size. For head and torso vertical displacements, the range in model kinematics was comparable to the range in volunteer kinematics. However, for forward displacements, the included parameters only explain some of the variability seen in the volunteer experiment. To conclude, the results indicate that the variation in volunteer vertical kinematics could be partly attributed to the variability in human characteristics analyzed in this study, while these cannot alone explain the variability in forward kinematics. The results can be used in future tuning of HBMs, and in future volunteer studies, when further investigating the potential causes of the large variability seen in occupant kinematics in evasive maneuvers.

Holistic pedestrian safety assessment for average males and females

Objective

An integrated assessment framework that enables holistic safety evaluations addressing vulnerable road users (VRU) is introduced and applied in the current study. The developed method enables consideration of both active and passive safety measures and distributions of real-world crash scenario parameters.

Methods

The likelihood of a specific virtual testing scenario occurring in real life has been derived from accident databases scaled to European level. Based on pre-crash simulations, it is determined how likely it is that scenarios could be avoided by a specific Autonomous Emergency Braking (AEB) system. For the unavoidable cases, probabilities for specific collision scenarios are determined, and the injury risk for these is determined, subsequently, from in-crash simulations with the VIVA+ Human Body Models combined with the created metamodel for an average male and female model. The integrated assessment framework was applied for the holistic assessment of car-related pedestrian protection using a generic car model to assess the safety benefits of a generic AEB system combined with current passive safety structures.

Results

In total, 61,914 virtual testing scenarios have been derived from the different car-pedestrian cases based on real-world crash scenario parameters. Considering the occurrence probability of the virtual testing scenarios, by implementing an AEB, a total crash risk reduction of 81.70% was achieved based on pre-crash simulations. It was shown that 50 in-crash simulations per load case are sufficient to create a metamodel for injury prediction. For the in-crash simulations with the generic vehicle, it was also shown that the injury risk can be reduced by implementing an AEB, as compared to the baseline scenarios. Moreover, as seen in the unavoidable cases, the injury risk for the average male and female is the same for brain injuries and femoral shaft fractures. The average male has a higher risk of skull fractures and fractures of more than three ribs compared to the average female. The average female has a higher risk of proximal femoral fractures than the average male.

Conclusions

A novel methodology was developed which allows for movement away from the exclusive use of standard-load case assessments, thus helping to bridge the gap between active and passive safety evaluations.

Development and validation of lumbar spine finite element model

The functional biomechanics of the lumbar spine have been better understood by finite element method (FEM) simulations. However, there are still areas where the behavior of soft tissues can be better modeled or described in a different way. The purpose of this research is to develop and validate a lumbar spine section intended for biomechanical research. A FE model of the 50th percentile adult male (AM) Total Human Model for Safety (THUMS) v6.1 was used to implement the modifications. The main modifications were to apply orthotropic material properties and nonlinear stress-strain behavior for ligaments, hyperelastic material properties for annulus fibrosus and nucleus pulposus, and the specific content of collagenous fibers in the annulus fibrosus ground substance. Additionally, a separation of the nucleus pulposus from surrounding bones and tissues was implemented. The FE model was subjected to different loading modes, in which intervertebral rotations and disc pressures were calculated. Loading modes contained different forces and moments acting on the lumbar section: axial forces (compression and tension), shear forces, pure moments, and combined loading modes of axial forces and pure moments. The obtained ranges of motion from the modified numerical model agreed with experimental data for all loading modes. Moreover, intradiscal pressure validation for the modified model presented a good agreement with the data available from the literature. This study demonstrated the modifications of the THUMS v6.1 model and validated the obtained numerical results with existing literature in the sub-injurious range. By applying the proposed changes, it is possible to better model the behavior of the human lumbar section under various loads and moments.

Development and preliminary validation of computationally efficient and detailed 50th percentile female human body models

OBJECTIVE

No vehicle testing standard (physical or computational) employs a mid-sized female human surrogate, despite discrepancies related to injury outcomes for female occupants amongst all vehicle users. We detail the design and preliminary validation of 50th percentile female (F50) computational human body models (HBMs) based on Global Human Body Models Consortium (GHBMC) models.

METHOD

Data for the target geometry was collected as part of the initial generation of GHBMC models. Imaging, surface data, and 15 anthropomorphic measures from a living female subject (60.8 kg and 1.61 m) served as the baseline for model development. Due to the role rib cage geometry plays in biomechanical loading, rib cage morphology from secondary retrospective data was leveraged to identify an average female rib cage based on gross anatomical features. A female rib cage was selected from an existing dataset closest to the mean depth, height, and width of the set, considering only those aged 20 - 50 years. The selected subject among this secondary set also exhibited a 7th rib angle and sternum angle within 5% of the mean measurements, and within the range of previously reported studies. The GHBMC 5th percentile, small female detailed (high biofidelity) and simplified (computationally efficient) models were morphed to match the F50 subject body surface, selected bones, and mean rib cage using established thin plate spline techniques. The models were validated vs. previously published literature studies with an emphasis on rib cage response. Model data was compared to 47 channels of experimental data across four biomechanical hub simulations, two sled test simulations (one of which included all female PMHS), and two robustness simulations to test stability. Model results were mass scaled to the average of the reported corridors. Objective evaluation was conducted using CORA. IRB approval was obtained for all prospective and retrospective data collected or used. The target rib cage was selected from retrospective image data used in prior studies (n = 339 chest CT scans).

RESULTS

The morphed HBMs closely matched the target geometry. The detailed and simplified models had masses and element counts of 61.2 kg and 61.8 kg, and 2.8 million and 0.3 million, respectively. The mass difference is due to a coarser mesh in the simplified model. The simplified model ran 23 times faster than the detailed model on the same hardware. Each model exhibited stability in robustness tests, and the average CORA scores were 0.80 and 0.72 in the detailed and simplified models, respectively. The models performed well in frontal impacts against PMHS corridors after mass scaling.

CONCLUSIONS

Numerous recent studies underscore poorer injury outcomes for female vehicle occupants compared to males. While such outcomes are multifactorial, the average female models introduced in this work offer a novel tool within a widely used family of HBMs to reduce the outcome gap in terms of injury for all drivers. HBMs can be deployed in safety studies or in future regulatory requirements faster and more economically than a resized or newly designed ATDs aimed at the same target population.

Cross-sectional properties of rib geometry from an adult population

Introduction: Human body models (HBMs) play a key role in improving modern vehicle safety systems to protect broad populations. However, their geometry is commonly derived from single individuals chosen to meet global anthropometric targets, thus their internal anatomy may not fully represent the HBM's target demographic. Past studies show sixth rib cross-sectional geometry differences between HBM ribs and population-derived ribs, and corrections to HBM ribs based on these data have improved HBM's abilities to predict rib fracture locations. Methods: We measure and report average and standard deviations (SDs) in rib cross-sectional geometric properties derived from live subject CT scans of 240 adults aged 18-90. Male and female results are given as functions of rib number and rib lengthwise position for ribs 2 through 11. Population means/SDs are reported for measures of rib total area, rib cortical bone area, and rib endosteal area, as well as inertial moment properties of these rib sections. These population corridors are compared between males and females, and against the baseline rib geometries defined in six current HBMs. Results: Total cross-sectional area results found average males ribs to be larger than those of females by between approximately 1-2 SDs depending on rib number and position, and larger in cortical bone cross-sectional area by between 0-1 SDs. Inertial moment ratios showed female ribs being between approximately 0-1 SDs more elongated than male ribs, dependent again on rib number and position. Rib cross-sectional areas from 5 of the 6 HBMs were found to be overly large along substantial portions of most ribs when compared to average population corridors. Similarly, rib aspect ratios in HBMs deviated from average population data by up to 3 SDs in regions towards sternal rib ends. Discussion: Overall, while most HBMs capture overall trends such as reductions in cross-section along shaft lengths, many also exhibit local variation that deviates from population trends. This study's results provide the first reference values for assessing the cross-sectional geometry of human ribs across a wide range of rib levels. Results also further provide clear guidelines to improve rib geometry definitions present in current HBMs in order to better represent their target demographic.

Personalization of human body models and beyond via image registration

Finite element human body models (HBMs) are becoming increasingly important numerical tools for traffic safety. Developing a validated and reliable HBM from the start requires integrated efforts and continues to be a challenging task. Mesh morphing is an efficient technique to generate personalized HBMs accounting for individual anatomy once a baseline model has been developed. This study presents a new image registration-based mesh morphing method to generate personalized HBMs. The method is demonstrated by morphing four baseline HBMs (SAFER, THUMS, and VIVA+ in both seated and standing postures) into ten subjects with varying heights, body mass indices (BMIs), and sex. The resulting personalized HBMs show comparable element quality to the baseline models. This method enables the comparison of HBMs by morphing them into the same subject, eliminating geometric differences. The method also shows superior geometry correction capabilities, which facilitates converting a seated HBM to a standing one, combined with additional positioning tools. Furthermore, this method can be extended to personalize other models, and the feasibility of morphing vehicle models has been illustrated. In conclusion, this new image registration-based mesh morphing method allows rapid and robust personalization of HBMs, facilitating personalized simulations.

Role of Rotated Head Postures on Volunteer Kinematics and Muscle Activity in Braking Scenarios Performed on a Driving Simulator

Occupants exposed to low or moderate crash events can already suffer from whiplash-associated disorders leading to severe and long-lasting symptoms. However, the underlying injury mechanisms and the role of muscle activity are not fully clear. Potential increases in injury risk of non-nominal postures, i.e., rotated head, cannot be evaluated in detail due to the lack of experimental data. Examining changes in neck muscle activity to hold and stabilize the head in a rotated position during pre-crash scenarios might provide a deeper understanding of muscle reflex contributions and injury mechanisms. In this study, the influence of two different head postures (nominal vs. rotation of the head by about 63 ± 9° to the right) on neck muscle activity and head kinematics was investigated in simulated braking experiments inside a driving simulator. The braking scenario was implemented by visualization of the virtual scene using head-mounted displays and a combined translational-rotational platform motion. Kinematics of seventeen healthy subjects was tracked using 3D motion capturing. Surface electromyography were used to quantify muscle activity of left and right sternocleidomastoideus (SCM) and trapezius (TRP) muscles. The results show clear evidence that rotated head postures affect the static as well as the dynamic behavior of muscle activity during the virtual braking event. With head turned to the right, the contralateral left muscles yielded higher base activation and delayed muscle onset times. In contrast, right muscles had much lower activations and showed no relevant changes in muscle activation between nominal and rotated head position. The observed delayed muscle onset times and increased asymmetrical muscle activation patterns in the rotated head position are assumed to affect injury mechanisms. This could explain the prevalence of rotated head postures during a crash reported by patients suffering from WAD. The results can be used for validating the active behavior of human body models in braking simulations with nominal and rotated head postures, and to gain a deeper understanding of neck injury mechanisms.

Efficient simulation strategy to design a safer motorcycle

This work presents models and simulations of a numerical strategy for a time and cost-efficient virtual product development of a novel passive safety restraint concept for motorcycles. It combines multiple individual development tasks in an aggregated procedure. The strategy consists of three successive virtual development stages with a continuously increasing level of detail and expected fidelity in multibody and finite element simulation environments. The results show what is possible with an entirely virtual concept study-based on the clever combination of multibody dynamics and nonlinear finite elements-that investigates the structural behavior and impact dynamics of the powered two-wheeler with the safety systems and the rider's response. The simulations show a guided and controlled trajectory and deceleration of the motorcycle rider, resulting in fewer critical biomechanical loads on the rider compared to an impact with a conventional motorcycle. The numerical research strategy outlines a novel procedure in virtual motorcycle accident research with different levels of computational effort and model complexity aimed at a step-by-step validation of individual components in the future.

Influences of human thorax variability on population rib fracture risk prediction using human body models

Rib fractures remain a common injury for vehicle occupants in crashes. The risk of a human sustaining rib fractures from thorax loading is highly variable, potentially due to a variability in individual factors such as material properties and geometry of the ribs and ribcage. Human body models (HBMs) with a detailed ribcage can be used as occupant substitutes to aid in the prediction of rib injury risk at the tissue level in crash analysis. To improve this capability, model parametrization can be used to represent human variability in simulation studies. The aim of this study was to identify the variations in the physical properties of the human thorax that have the most influence on rib fracture risk for the population of vehicle occupants. A total of 15 different geometrical and material factors, sourced from published literature, were varied in a parametrized SAFER HBM. Parametric sensitivity analyses were conducted for two crash configurations, frontal and near-side impacts. The results show that variability in rib cortical bone thickness, rib cortical bone material properties, and rib cross-sectional width had the greatest influence on the risk for an occupant to sustain two or more fractured ribs in both impacts. Therefore, it is recommended that these three parameters be included in rib fracture risk analysis with HBMs for the population of vehicle occupants.