Quantitative cervical spine injury responses in whiplash loading with a numerical method of natural neural reflex consideration.

BACKGROUND AND OBJECTIVE: Neural reflex is hypothesized as a regulating step in spine stabilizing system. However, neural reflex control is still in its infancy to consider in the previous finite element analysis of head-neck system for various applications. The purpose of this study is to investigate the influences of neural reflex control on neck biomechanical responses, then provide a new way to achieve an accurate biomechanical analysis for head-neck system with a finite element model. METHODS: A new FE head-neck model with detailed active muscles and spinal cord modeling was established and globally validated at multi-levels. Then, it was coupled with our previously developed neuromuscular head-neck model to analyze the effects of vestibular and proprioceptive reflexes on biomechanical responses of head-neck system in a typical spinal injury loading condition (whiplash). The obtained effects were further analyzed by comparing a review of epidemiologic data on cervical spine injury situations. RESULT: The results showed that the active model (AM) with neural reflex control obviously presented both rational head-neck kinematics and tissue injury risk referring to the previous experimental and epidemiologic studies, when compared with the passive model (PM) without it. Tissue load concentration locations as well as stress/strain levels were both changed due to the muscle activation forces caused by neural reflex control during the whole loading process. For the bony structures, the AM showed a peak stress level accounting for only about 25% of the PM. For the discs, the stress concentrated location was transferred from C2-C6 in the PM to C4-C6 in the AM. For the spinal cord, the strain concentrated locations were transferred from C1 segment to around C4 segment when the effects of neural reflex control were implemented, while the gray matter and white matter peak strains were reduced to 1/3 and 1/2 of the PM, respectively. All these were well correlated with epidemiological studies on clinical cervical spine injuries. CONCLUSION: In summary, the present work demonstrated necessity of considering neural reflex in FE analysis of a head-neck system as well as our model biofidelity. Overall results also verified the previous hypothesis and further quantitatively indicated that the muscle activation caused by neural reflex is providing a protection for the neck in impact loading by decreasing the strain level and changing the possible injury to lower spinal cord level to reduce injury severity.

Retrospective evaluation of vehicle whiplash-reducing head restraint systems to prevent whiplash injury in Victoria, Australia.

Head restraint systems specifically engineered to reduce the impact of whiplash injury in the event of a rear-end collision were introduced in the late 1990s with the aim of reducing whiplash injury risk that went 'beyond simple geometric improvements' to head restraints. Whilst studies have shown that whiplash-reducing head restraint systems are highly effective in reducing whiplash injury, these were based on a limited range of systems including Toyota's Whiplash Injury Lessening (WIL) seating system, Volvo's Whiplash Injury Prevention System (WHIPS) and the Saab Active Head Restraint (SAHR) and have generally focussed on Swedish crash and insurance data. However, there has been no broad real-world crash-based evaluation of the effectiveness of whiplash-reducing head restraint systems currently present in the vehicle fleet that validates the results of these studies in other populations. The objective of this study was to undertake a retrospective evaluation of vehicle whiplash-reducing head restraint systems to prevent whiplash injury using real-world crash data linked to insurance claims data in Victoria, Australia. It was found that whiplash-reducing head restraint systems are associated with a statistically significant reduction in the odds of driver and front seat passenger whiplash injury in a vehicle struck in a rear-end collision of 11.6 % (95 % CI 0.20 %, 21.6 %). The results indicate that whiplash-reducing head restraint systems are an effective technology for reducing the risk of whiplash injury to drivers and front seat passengers in a vehicle struck in a rear-end collision. Considering that around a quarter of all casualty crashes involving passenger and light commercial vehicles are rear-end, the fitment of whiplash-reducing head restraint systems to all vehicles as a standard safety feature would likely see a significant reduction in the incidence of whiplash injury.

A comparison of anti-whiplash seats during low/moderate speed rear-end collisions.

Objectives: The Insurance Institute for Highway Safety (IIHS) rates automotive seats as good, acceptable, marginal, and poor on their abilities to prevent whiplash injuries during rear-end collisions. The goal of this study was to compare the performance of some good- and poor-rated seats at speed changes below 16 km/h where some whiplash injuries occur.Methods: A BioRID II anthropometric test device (ATD) underwent rear-end collisions from 2 to 14 km/h while seated on one of two Volvo Whiplash Prevention seats (WHIPS), a Saab Active Head Restraint seat (SAHR), or a General Motors High Retention seat (GMHR). The WHIPS and SAHR seats were rated good whereas the GMHR seat was rated poor by the IIHS. The ATD's kinematics, kinetics and three neck injury criteria were evaluated across the range of collision severities.Results: Most of the head and torso kinematics, kinetics and injury criteria exhibited graded responses with increasing collision severities. Only head extension angle remained relatively similar across all speed changes. Differences between the good- and poor-rated seats were most apparent in the upper neck loads and moments, and head retraction for speed changes greater than 6 km/h.Conclusions: The relatively similar occupant responses across all seats could explain the marginal reductions in whiplash injury risk between good- and poor-rated seats in field studies. Further research into the design of anti-whiplash devices is required to better understand the link between occupant response and injury, and to better mitigate the risk of whiplash injuries during rear-end collisions.

Comparison of control strategies for the cervical muscles of an average female head-neck finite element model.

Objective: ViVA OpenHBM is the first open source Human Body Model (HBM) for crash safety assessment. It represents an average size (50th percentile) female and was created to assess whiplash protection systems in a car. To increase the biofidelity of the current model, further enhancements are being made by implementing muscle reflex response capabilities as cervical muscles alter the head and neck kinematics of the occupant during low-speed rear crashes. The objective of this study was to assess how different neck muscle activation control strategies affect head-neck kinematics in low speed rear impacts.Methods: The VIVA OpenHBM head-neck model, previously validated to PMHS data, was used for this study. To represent the 34 cervical muscles, 129 beam elements with Hill-type material models were used. Two different muscle activation control strategies were implemented: a control strategy to mimic neural feedback from the vestibular system and a control strategy to represent displacement feedback from muscle spindles. To identify control gain values for these controller strategies, parameter calibrations were conducted using optimization. The objective of these optimizations was to match the head linear and angular displacements measured in volunteer tests.Results: Muscle activation changed the head kinematics by reducing the peak linear displacements, as compared to the model without muscle activation. For the muscle activation model mimicking the human vestibular system, a good agreement was observed for the horizontal head translation. However, in the vertical direction there was a discrepancy of head kinematic response caused by buckling of the cervical spine. In the model with a control strategy that represents muscle spindle feedback, improvements in translational head kinematics were observed and less cervical spine buckling was observed. Although, the overall kinematic responses were better in the first strategy.Conclusions: Both muscle control strategies improved the head kinematics compared to the passive model and comparable to the volunteer kinematics responses with overall better agreement achieved by the model with active muscles mimicking the human vestibular system.

Average male and female virtual dummy model (BioRID and EvaRID) simulations with two seat concepts in the Euro NCAP low severity rear impact test configuration.

Soft tissue neck injuries, also referred to as whiplash injuries, which can lead to long term suffering accounts for more than 60% of the cost of all injuries leading to permanent medical impairment for the insurance companies, with respect to injuries sustained in vehicle crashes. These injuries are sustained in all impact directions, however they are most common in rear impacts. Injury statistics have since the mid-1960s consistently shown that females are subject to a higher risk of sustaining this type of injury than males, on average twice the risk of injury. Furthermore, some recently developed anti-whiplash systems have revealed they provide less protection for females than males. The protection of both males and females should be addresses equally when designing and evaluating vehicle safety systems to ensure maximum safety for everyone. This is currently not the case. The norm for crash test dummies representing humans in crash test laboratories is an average male. The female part of the population is not represented in tests performed by consumer information organisations such as NCAP or in regulatory tests due to the absence of a physical dummy representing an average female. Recently, the world first virtual model of an average female crash test dummy was developed. In this study, simulations were run with both this model and an average male dummy model, seated in a simplified model of a vehicle seat. The results of the simulations were compared to earlier published results from simulations run in the same test set-up with a vehicle concepts seat. The three crash pulse severities of the Euro NCAP low severity rear impact test were applied. The motion of the neck, head and upper torso were analysed in addition to the accelerations and the Neck Injury Criterion (NIC). Furthermore, the response of the virtual models was compared to the response of volunteers as well as the average male model, to that of the response of a physical dummy model. Simulations with the virtual male and female dummy models revealed differences in dynamic response related to the crash severity, as well as between the two dummies in the two different seat models. For the comparison of the response of the virtual models to the response of the volunteers and the physical dummy model, the peak angular motion of the first thoracic vertebra as found in the volunteer tests and mimicked by the physical dummy were not of the same magnitude in the virtual models. The results of the study highlight the need for an extended test matrix that includes an average female dummy model to evaluate the level of occupant protection different seats provide in vehicle crashes. This would provide developers with an additional tool to ensure that both male and female occupants receive satisfactory protection and promote seat concepts that provide the best possible protection for the whole adult population. This study shows that using the mathematical models available today can provide insights suitable for future testing.

Risk of concussion due to head acceleration in rear impact sled tests of passenger automobile seats.

OBJECTIVE: Acceleration-based injury metrics can be useful for quantitatively evaluating risk of concussion (a form of mild traumatic brain injury, or mTBI) after automobile collisions, especially when objective medical findings may be negative, as in many cases of concussion. In the present study, head acceleration data were used to evaluate the risk of concussion or more serious head injury to the driver of an automobile that experiences a rear impact resulting in a forward change in velocity (delta-V) of 15.5 km/h (9.6 mph). METHODS: Data were collected from 34 Insurance Institute for Highway Safety (IIHS) rear impact sled tests conducted from 2009 through 2017 for driver seats from 10 passenger car models leading in U.S. sales in 2017. Resultant translational head acceleration data were used to compute the head injury criterion (HIC; HIC15, HIC36) and A-3ms (the 3-ms resultant acceleration criterion utilized by the European New Car Assessment Protocol and others), and maximum resultant translational acceleration (aT). Maximum resultant rotational acceleration (aR) was estimated based on Biofidelic Rear Impact Dummy (BioRID) data from Welch et al. ( 2010 ). RESULTS: No sled test included in the study resulted in a HIC15 value exceeding 55, a HIC36 value exceeding 85, A-3ms exceeding 28 g, aT exceeding 28 g, or estimated aR exceeding 1,400 rad/s2. These values are far below published automotive injury risk values (IARV) used to evaluate crashworthiness. Further, contemporary concussion risk curves place the HIC15, aT, aR, and paired combination of aT and aR sustained by the BioRID anthropomorphic test dummy (ATD) in the IIHS tests at a negligible risk of concussion (mTBI). CONCLUSIONS: The 15.5 km/h delta-V IIHS rear impact sled tests conducted between 2009 and 2017 for common passenger automobile driver seats resulted in injury metrics associated with minimal risk of concussion or more severe head injuries.

Real-world adjustments of driver seat and head restraint in Saab 9-3 vehicles.

OBJECTIVE: Whiplash-associated disorder (WAD), commonly denoted whiplash injury, is a worldwide problem. These injuries occur at relatively low changes of velocity (typically <25 km/h) in impacts from all directions. Rear impacts, however, are the most common in the injury statistics. Females have a 1.5-3 times higher risk of whiplash injury than males. Improved seat design is the prevailing means of increasing the protection of whiplash injury for occupants in rear impacts. Since 1997, more advanced whiplash protection systems have been introduced on the market, the Saab Active Head Restraint (SAHR) being one of the most prominent. The SAHR-which is height adjustable-is mounted to a pressure plate in the seatback by means of a spring-resisted link mechanism. Nevertheless, studies have shown that seats equipped with reactive head restraints (such as the SAHR) have a very high injury-reducing effect for males (∼60-70%) but very low or no reduction effect for females. One influencing factor could be the position of the head restraint relative to the head, because a number of studies have reported that adjustable head restraints often are incorrectly positioned by drivers. The aim was to investigate how female and male Saab drivers adjust the seat in the car they drive the most. METHODS: The seated positions of drivers in stationary conditions have been investigated in a total of 76 volunteers (34 females, 42 males) who participated in the study. Inclusion criteria incorporated driving a Saab 9-3 on a regularly basis. RESULTS: The majority of the volunteers (89%) adjusted the head restraint to any of the 3 uppermost positions and as many as 59% in the top position. The average vertical distance between the top of the head and the top of the head restraint (offset) increase linearly with increasing statures, from an average of -26 mm (head below the head restraint) for small females to an average of 82 mm (head above the head restraint) for large males. On average, the offset was 23 mm for females, which is within a satisfactory range and in accordance with recommendations; the corresponding value for males was 72 mm. The backset tended to be shorter among female volunteers (on average 27 mm) compared to the male volunteers (on average 44 mm). Moreover, the backset tended to increase with increasing statures. CONCLUSIONS: Incorrect adjustment of the head restraint cannot explain the large differences found between the sexes in the effectiveness of the SAHR system.

Preventable Injuries/Fatalities Due to Distracted Driving: A Call for a Coordinated Action.

In the past decade, distracted driving has emerged as one of the most prominent global road safety concerns. The singular and combined efforts of many organizations, such as Drop It And Drive (DIAD) and the Traffic Injury Research Foundation (TIRF), have identified the need for partnerships, shared information, and access to interpretable research findings to guide decision making and to identify effective strategies to reduce, if not eliminate, preventable injuries/fatalities from distracted driving, including whiplash-associated disorders. This editorial describes activities in 5 target areas identified in our environmental scan in Canada: (1) provincial/territorial government strategies, (2) enforcement, (3) data collection and measurement, (4) awareness campaigns, and (5) legislation. We will also reinforce the potential benefits of seeking and establishing meaningful interdisciplinary partnerships to reduce distracted driving across the globe. Finally, this editorial provides an example of how these interdisciplinary partnerships can help reduce preventable, life-altering injuries/deaths caused by distracted driving. J Orthop Sports Phys Ther 2016;46(10):818-821. doi:10.2519/jospt.2016.0113.

An energy-absorbing sliding seat for reducing neck injury risks in rear impact--analysis for prototype built.

OBJECTIVE: This study investigated overall performance of an energy-absorbing sliding seat concept for whiplash neck injury prevention. The sliding seat allows its seat pan to slide backward for some distance under certain restraint force to absorb crash energy in rear impacts. METHODS: A numerical model that consisted of vehicle interior, seat, seat belt, and BioRID II dummy was built in MADYMO to evaluate whiplash neck injury in rear impact. A parametric study of the effects of sliding seat parameters, including position and cushion stiffness of head restraint, seatback cushion stiffness, recliner characteristics, and especially sliding energy-absorbing (EA) restraint force, on neck injury criteria was conducted in order to compare the effectiveness of the sliding seat concept with that of other existing anti-whiplash mechanisms. Optimal sliding seat design configurations in rear crashes of different severities were obtained. A sliding seat prototype with bending of a steel strip as an EA mechanism was fabricated and tested in a sled test environment to validate the concept. The performance of the sliding seat under frontal and rollover impacts was checked to make sure the sliding mechanism did not result in any negative effects. RESULTS: The protective effect of the sliding seat with EA restraint force is comparable to that of head restraint-based and recliner stiffness-based anti-whiplash mechanisms. EA restraint force levels of 3 kN in rear impacts of low and medium severities and 6 kN in impacts of high severity were obtained from optimization. In frontal collision and rollover, compared to the nonsliding seat, the sliding seat does not result in any negative effects on occupant protection. The sled test results of the sliding seat prototype have shown the effectiveness of the concept for reducing neck injury risks. CONCLUSION: As a countermeasure, the sliding seat with appropriate restraint forces can significantly reduce whiplash neck injury risk in rear impacts of low, medium, and high severities with no negative effects on other crash load cases.

Loud preimpact tones reduce the cervical multifidus muscle response during rear-end collisions: a potential method for reducing whiplash injuries.

BACKGROUND CONTEXT: Neck muscle responses after unexpected rear-end collisions consist of a stereotypical combination of postural and startle responses. Prior work using surface electromyography (EMG) has shown that the superficial neck muscle responses can be attenuated when a loud tone (105 dB) is presented 250 milliseconds before impact, but the accompanying response of the deeper multifidus muscles remains unknown. Quantifying this response in multifidus is important because this muscle attaches directly to the cervical facet capsule and can potentially increase the strain in the capsule during an impact and contribute to whiplash injury. PURPOSE: To investigate if a loud preimpact tone decreases the cervical multifidus muscle response during rear-end perturbations. STUDY DESIGN: After approval by the University Clinical Ethics Review Board, human volunteers experienced a series of three whiplash-like perturbations. PATIENT SAMPLE: Twelve subjects with no history of neurologic disorders or whiplash injury were recruited to participate in this experiment. OUTCOME MEASURES: Bilateral indwelling EMG of multifidus at the C4 and C6 levels, surface EMG of sternocleidomastoid (SCM) and C4 paraspinals (PARAs), and kinematics of the head/neck were measured. METHODS: Subjects experienced three whiplash-like perturbations (peak acceleration of 19.5 m/s(2)) preceded by either no tone or a loud tone (105 dB) presented 250 milliseconds before sled acceleration onset. RESULTS: The loud tone decreased the muscle activity of C6 multifidus (42%) and C4 PARAs (30%), but did not affect the C4 multifidus or SCM activity. Peak head kinematic responses (extension angle: 6%, retraction: 9%, linear forward acceleration: 9%, and angular acceleration in extension: 13%) were also decreased by the loud preimpact tone. CONCLUSIONS: The attenuation of peak C6 multifidus activity and head kinematic responses suggests that a loud preimpact tone may reduce the strain in the cervical facet capsule, which may reduce the risk of whiplash injury during rear-end collisions.

Verification of whiplash-associated disorders in forensic medical practice. part I--assessment of the injury circumstances and biomechanics.

For many years, researchers involved in automotive industry and forensic medicine, as well as insurance companies have shown great interest in the issues of etiology and prevention of cervical spine distortion. The etiopathogenesis of whiplash-associated disorders (WADs) remains controversial and its morphological determinants have not been explicitly determined to date. The subjective nature of complaints causes great difficulties in objective assessment of the consequences of acceleration-deceleration injuries and in verification of compensation claims. The objective of the study was to present biomechanical relationships and circumstances accompanying WADs using population-based studies, statistical data of insurance companies and analysis of recordings of event data recorders installed by vehicle producers. The knowledge of technical aspects of WAD circumstances should facilitate medical assessment of the above-mentioned consequences.

A test-based method for the assessment of pre-crash warning and braking systems.

In this paper, a test-based assessment method for pre-crash warning and braking systems is presented where the effectiveness of a system is measured by its ability to reduce the number of injuries of a given type or severity in car-to-car rear-end collisions. Injuries with whiplash symptoms lasting longer than 1 month and MAIS2+ injuries in both vehicles involved in the crash are considered in the assessment. The injury reduction resulting from the impact speed reduction due to a pre-crash system is estimated using a method which has its roots in the dose-response model. Human-machine interaction is also taken into account in the assessment. The results reflect the self-protection as well as the partner-protection performance of a pre-crash system in the striking vehicle in rear-end collisions and enable a comparison between two or more systems. It is also shown how the method may be used to assess the importance of warning as part of a pre-crash system.

ADSEAT--Adaptive Seat to Reduce Neck Injuries for Female and Male Occupants.

Neck injuries sustained in low severity vehicle crashes are of worldwide concern and the risk is higher for females than for males. The objective of the study was to provide guidance on how to evaluate protective performance of vehicle seat designs aiming to reduce the incidence of neck injuries for female and male occupants. The objective was achieved by reviewing injury risk, establishing anthropometric data of an average female, performing dynamic volunteer tests comprising females and males, and developing a finite element model, EvaRID, of an average female. With respect to injury criteria, it was concluded based on the tests that using NIC (with a lower threshold value) and Nkm (with reduced intercept values) for females would be a suitable starting point. Virtual impact simulations with seats showed that differences were found in the response of the BioRID II and EvaRID models, for certain seats.

A brief educational program improves awareness regarding whiplash prevention among a cohort of vehicle fleet managers in British Columbia, Canada.

OBJECTIVE: Previous research indicates that most vehicle occupants are unaware that a correctly adjusted, well-designed vehicular head restraint provides substantial protection against whiplash injuries. This study examined whether a brief educational intervention could improve awareness regarding whiplash injuries and prevention strategies among a cohort of vehicle fleet managers. METHODS: A brief written survey was administered prior to, and approximately 1 h after a 30-min presentation on whiplash injury and prevention measures, which was delivered at a regional fleet manager meeting held in British Columbia, Canada (n = 27 respondents). RESULTS: Respondents had low baseline knowledge levels regarding the causes, consequences, and prevention of whiplash. Following the presentation, however, respondents improved awareness in all of these domains and, most important, reported an increased motivation to implement changes based on this newly acquired knowledge. CONCLUSIONS: These results indicate that improved education practices and social marketing tools are potentially valuable to increase awareness among relevant stakeholders.

The startle response during whiplash: a protective or harmful response?

Whiplash injuries are common following rear-end collisions. During such collisions, initially relaxed occupants exhibit brisk, stereotypical muscle responses consisting of postural and startle responses that may contribute to the injury. Using prestimulus inhibition, we sought to determine if the startle response elicited during a rear-end collision contributes to head stabilization or represents a potentially harmful overreaction of the body. Three experiments were performed. In the first two experiments, two groups of 14 subjects were exposed to loud tones (124 dB) preceded by prestimulus tones at either four interstimulus intervals (100-1,000 ms) or five prestimulus intensities (80-124 dB). On the basis of the results of the first two experiments, 20 subjects were exposed to a simulated rear-end collision (peak sled acceleration = 2 g; speed change = 0.75 m/s) preceded by one of the following: no prestimulus tone, a weak tone (85 dB), or a loud tone (105 dB). The prestimulus tones were presented 250 ms before sled acceleration onset. The loud prestimulus tone decreased the amplitude of the sternocleidomastoid (16%) and cervical paraspinal (29%) muscles, and key peak kinematics: head retraction (17%), horizontal head acceleration (23%), and head angular acceleration in extension (23%). No changes in muscle amplitude or kinematics occurred for the weak prestimulus. The reduced muscle and kinematic responses observed with loud tones suggest that the startle response represents an overreaction that increases the kinematics in a way that potentially increases the forces and strains in the neck tissues. We propose that minimizing this overreaction during a car collision may decrease the risk of whiplash injuries.

Cervical neural space narrowing during simulated rear crashes with anti-whiplash systems.

PURPOSE: Chronic radicular symptoms have been documented in whiplash patients, potentially caused by cervical neural tissue compression during an automobile rear crash. Our goals were to determine neural space narrowing of the lower cervical spine during simulated rear crashes with whiplash protection system (WHIPS) and active head restraint (AHR) and to compare these data to those obtained with no head restraint (NHR). We extrapolated our results to determine the potential for cord, ganglion, and nerve root compression. METHODS: Our model, consisting of a human neck specimen within a BioRID II crash dummy, was subjected to simulated rear crashes in a WHIPS seat (n = 6, peak 12.0 g and ΔV 11.4 kph) or AHR seat and subsequently with NHR (n = 6, peak 11.0 g and ΔV 10.2 kph with AHR; peak 11.5 g and ΔV 10.7 kph with NHR). Cervical canal and foraminal narrowing were computed and average peak values statistically compared (P < 0.05) between WHIPS, AHR, and NHR. RESULTS: Average peak canal and foramen narrowing could not be statistically differentiated between WHIPS, AHR, or NHR. Peak narrowing with WHIPS or AHR was 2.7 mm for canal diameter and 1.6 mm, 2.7 mm, and 5.9 mm(2) for foraminal width, height and area, respectively. CONCLUSIONS: While lower cervical spine cord compression during a rear crash is unlikely in those with normal canal diameters, our results demonstrated foraminal kinematics sufficient to compress spinal ganglia and nerve roots. Future anti-whiplash systems designed to reduce cervical neural space narrowing may lead to reduced radicular symptoms in whiplash patients.

Vehicle head restraint positioning knowledge and behaviours in a sample of Irish drivers.

A correctly positioned vehicle head restraint (HR) can reduce whiplash injury risk in collisions, however, HRs are often sub-optimally positioned. The primary aim of this study was to investigate vehicle HR position and driver knowledge of correct HR positioning in an Irish population. Secondary aims were to investigate the associations with driver age, gender and vehicle age. Data collection involved HR measurement and a driver questionnaire (n = 110). Just 27% of drivers had optimal HR positioning, while 30% had poor or marginal positioning. Newer vehicles (<5 years old) had better positioned HR in the horizontal plane (p = 0.036), than older vehicles. Younger drivers (<30 years) were more likely to have poorer positioning of HR (p = 0.002), than the 30 years or over group. Females were more likely to have better vertical positioning of their HR (p = 0.003) than males. Driver knowledge of correct position was variable, and not associated with actual HR position, with 65% knowing the correct vertical positioning standard but only 27% identifying the correct horizontal position. Many drivers have inadequately positioned HR, which needs to be addressed by improved vehicle design and public education.

Articulation at shoulder level--a pilot experimental study on car seat comfort.

This article reports on a pilot experimental study aimed at a first evaluation of the introduction of an articulation in the upper part of the seat backrest. The idea of introducing this articulation sprang from prevention of whiplash injuries and this study tentatively assesses its potential for improvement in comfort. This was done considering a pre-defined articulation height. A height for the articulation of 43.5 cm above the H-point of a reference seat was theoretically deduced based on a population with an average sitting height of 88 cm. Participants evaluated the articulated seat in comparison with the reference seat. Twelve participants were divided into three groups of sitting height. In a laboratory environment subjective comfort evaluations and preferred values of deployment of the articulation and of counter-tilting of the headrest were registered. Driving on the roads completed and validated the laboratory assessments. The reference seat was deemed less comfortable for the participants with short and medium sitting height than for the tall ones. There was a notable improvement in comfort for most of the medium and short sitting height participants when using the articulated seat. The articulation was fully deployed by most participants.

What occupant kinematics and neuromuscular responses tell us about whiplash injury.

STUDY DESIGN: Literature-based review. OBJECTIVE: To review the published data on occupant kinematic and neuromuscular responses during low-speed impacts and analyze how these data inform our understanding of whiplash injury. SUMMARY OF BACKGROUND DATA: A stereotypical kinematic and neuromuscular response has been observed in human subjects exposed to rear-end impacts. Combined with various models of injury, these response data have been used to develop anti-whiplash seats that prevent whiplash injury in many, but not all, individuals exposed to a rear-end crash. METHODS: Synthesis of the literature. RESULTS: Understanding of the occupant kinematics and neuromuscular responses, combined with data from various seat-related interventions, have shown that differential motion between the superior and inferior ends of the cervical spine is responsible for many whiplash injuries. The number of whiplash injuries not prevented by current anti-whiplash seats suggests than further work remains, possibly related to designing seats that respond dynamically to the occupant and collision properties. Neck muscles alter the head and neck kinematics during the interval in which injury likely occurs, even in initially relaxed occupants. It remains unclear whether muscle activation mitigates or exacerbates whiplash injury. If muscle activation mitigates injury, then advance warning could be used to help occupant tense their muscles before impact. Alternatively, if muscle activation exacerbates whiplash injury, then a loud preimpact sound that uncouples the startle and postural components of the muscle response could reduce peak muscle activation during a whiplash exposure. CONCLUSION: Our improved understanding of whiplash injury has led to anti-whiplash seats that have prevented many whiplash injuries. Further work remains to optimize these and possibly other systems to further reduce the number of whiplash injuries.