Neck Forces Research Articles

Biomechanical Analysis of Football Neck Collars

To determine the load-limiting capabilities of protective neck collars used in football through dynamic impact testing. A 50th-percentile male Hybrid III dummy was used in 48 dynamic impact tests comparing The Cowboy Collar, Bullock Collar, and Kerr Collar. A control and each collar were tested at two velocities (5 m/s and 7 m/s), three impact locations (front, top, and side of the helmet), and two shoulder pad positions (normal and raised). Research laboratory. None. None. Independent variables were the neck collars, impact velocity, and shoulder pad position. In addition to range of motion, upper and lower neck forces and moments were measured. With the top impact location, it was found that the Kerr Collar and Bullock Collar reduced head accelerations and force transmission through the neck. With the front impact location, all the collars reduced lower neck moment. The Kerr Collar was also capable of reducing the lower neck force and upper neck moment. With the side impact location, the Kerr Collar substantially reduced lower neck moment. These reductions in loads correlate with the degree to which each collar restricted the motion of the head and neck. By restricting the range of motion of the neck and redistributing load to the shoulders, neck loads can be effectively lowered.

Differentiating Effortful and Noneffortful Swallowing with a Neck Force Transducer: Implications for the Development of a Clinical Feedback System

This study sought to determine whether effortful saliva swallows could be differentiated from habitual, noneffortful saliva swallows on the basis of swallow-related changes in neck circumference in humans. Gender differences in swallow-related neck circumference were examined as a secondary question. Twenty-seven healthy adults (14 females; mean age = 26.6 years, SD = 3.9 years) participated in two experimental runs (run duration = 10 min) during which they produced single trials of three visually cued tasks in random order: effortful saliva swallowing, saliva swallowing, and a control task involving repetitive apposition of the dominant thumb and index finger. Neck and ribcage circumference were simultaneously collected from the output of force transducers positioned around the neck and ribcage, respectively. The primary outcome variables were the positive and negative voltage peak amplitudes associated with changes in neck circumference during single-swallow trials. Effects of the swallowing task on positive and negative voltage peaks were examined with separate two-way analysis of variance procedures. Results indicated that both positive (F = 6.49, p < 0.05) and negative (F = 12.05, p <or= .05) voltage peaks were significantly greater for effortful swallows compared with those for noneffortful swallows. The gender main effect and the swallow type by gender interaction were not significant. Effortful and noneffortful swallows of saliva can be differentiated from the output of a noninvasive force transducer worn around the neck. This type of physiologic recording may have potential as a biofeedback technique in training dysphagic patients on the effortful swallow maneuver.

Upper Neck Forces and Moments and Cranial Angular Accelerations in Lateral Impact

Biomechanical studies using postmortem human subjects (PMHS) in lateral impact have focused primarily on chest and pelvis injuries, mechanisms, tolerances, and comparison with side impact dummies. A paucity of data exists on the head-neck junction, i.e., forces and moments, and cranial angular accelerations. The objective of this study was to determine lateral impact-induced three-dimensional temporal forces and moments at the head-neck junction and cranial linear and angular accelerations from sled tests using PMHS and compare with responses obtained from an anthropomorphic test device (dummy) designed for lateral impact. Following initial evaluations, PMHS were seated on a sled, restrained using belts, and lateral acceleration was applied. Specimens were instrumented with a pyramid-shaped nine-accelerometer package to record cranial accelerations. A sled accelerometer was used to record the input acceleration. Radiographs and computed tomography scans were obtained to identify pathology. A similar testing protocol was adopted for dummy tests. Results indicated that profiles of forces and moments at the head-neck junction and cranial accelerations were similar between the two models. However, peak forces and moments at the head-neck junction were lower in the dummy than PMHS. Peak cranial linear and angular accelerations were also lower in the dummy than in the PMHS. Fractures to the head-neck complex were not identified in PMHS tests. Peak cranial angular accelerations were suggestive of mild traumatic brain injury with potential for loss of consciousness. Findings from this study with a limited dataset are valuable in establishing response corridors for side impacts and evaluating side impact dummies used in crashworthiness and safety-engineering studies.

Force production and EMG activity of neck muscles in adolescent headache

Purpose. This study compared the maximal force, EMG/force ratio and co-activation characteristics of the neck-shoulder muscles between 30 adolescents with migraine-type headache, 29 with tension-type headache, and 30 headache-free controls.Method. Force was measured with surface electromyography (EMG) from the cervical erector spinae (CES), the sternocleidomastoid (SCM) and trapezius muscles during the maximal isometric neck flexion, neck extension and shoulder flexion.Results. Girls with migraine-type headache had higher EMG/force ratios between the EMG of the left agonist SCM muscle and the corresponding maximal neck flexion (p = 0.030) and neck rotation force to the right side (p = 0.024) than the girls with tension-type headache. Migrainous girls had more co-activation of right antagonist CES muscle during maximal neck flexion force than the girls without headache (p = 0.015). Neck force production showed no significant differences between girls. Girls with tension-type headache displayed lower left shoulder flexion force than girls with migraine-type headache (p = 0.005) or with no headache (p = 0.005). In boys, no significant differences were observed.Conclusions. Girls with tension-type headache and migraine-type headache have differences in neuromuscular function in the neck-shoulder muscles. The data amplify our knowledge of the neck-shoulder muscle dysfunction in adolescent headache, and may encourage the use of specific rehabilitation methods in the management of different types of headache.

Child restraint seat design considerations to mitigate injuries to three-year-old children in side impact crashes

This research focuses on the injury potential of children seated in forward-facing child safety seats during side impact crashes in a far-side seated position. Side impact dynamic sled tests were conducted by Transportation Research Center Inc. (TRC) using two Hybrid III 3-year-old child dummies in convertible forward/rearward child safety seats. The seats were equipped with a LATCH and a top tether and the dummies were positioned in forward-facing/far-side configuration. The tests were completed using an acceleration pulse with a closing speed of 32.8 km/h, and the seat fixture with vehicle body oriented at 270° relative to the motion of the sled. A fully deformable finite element model of a child restraint seat, for side impact crash investigations, has been developed which has also been previously validated for frontal impacts. A numerical model employing a similar set-up as the experimental sled test was generated and simulated using LSDYNA. The numerical model was validated by comparing the head and the chest accelerations, resultant upper and lower neck forces and moments from the experimental and numerical tests. The simulation results were observed to be in good agreement to the experimental observations. Further studies were conducted to confine lateral movement of the dummy's head by adding energy absorbing foam on the side wings in the vicinity of the contact region of the CRS. It was observed from the simulation results that the addition of foam padding and foam blocks was effective in reducing the head injury criteria of the Hybrid III 3-year-old dummy by approximately 30%, and the upper neck lateral shear and lateral bending by approximately 45%.

Occupant Dynamics in Rollover Crashes: Influence of Roof Deformation and Seat Belt Performance on Probable Spinal Column Injury

Motor vehicle crashes are the leading cause of death in the United States for people ages 3–33, and rollover crashes have a higher fatality rate than any other crash mode. At the request and under the sponsorship of Ford Motor Company, Autoliv conducted a series of dynamic rollover tests on Ford Explorer sport utility vehicles (SUV) during 1998 and 1999. Data from those tests were made available to the public and were analyzed in this study to investigate the magnitude of and the temporal relationship between roof deformation, lap–shoulder seat belt loads, and restrained anthropometric test dummy (ATD) neck loads.During each of the three FMVSS 208 dolly rollover tests of Ford Explorer SUVs, the far-side, passenger ATDs exhibited peak neck compression and flexion loads, which indicated a probable spinal column injury in all three tests. In those same tests, the near-side, driver ATD neck loads never predicted a potential injury. In all three tests, objective roof/pillar deformation occurred prior to the occurrence of peak neck loads (Fz, My) for far-side, passenger ATDs, and peak neck loads were predictive of probable spinal column injury. The production lap and shoulder seat belts in the SUVs, which restrained both driver and passenger ATDs, consistently allowed ATD head contact with the roof while the roof was contacting the ground during this 1000 ms test series. Local peak neck forces and moments were noted each time the far-side, passenger ATD head contacted (“dived into”) the roof while the roof was in contact with the ground; however, the magnitude of these local peaks was only 2–13% of peak neck loads in all three tests. “Diving-type” neck loads were not predictive of injury for either driver or passenger ATD in any of the three tests.

Reconstruction of Crashes Involving Injured Child Occupants: The Risk of Serious Injuries Associated with Sub-Optimal Restraint Use May Be Reduced by Better Controlling Occupant Kinematics

Objective. To determine whether injuries to sub-optimally restrained child occupants in real-world crashes were likely to be preventable by alternative restraint usage practices and to assess the usefulness of crash reconstruction for exploring injury mechanisms in child occupants. Methods. Real-world crashes in which child occupants sustained significant injuries were reconstructed on a laboratory crash sled using the Hybrid III family of child dummies. Alternative restraint scenarios and cases in which children were not seriously injured were also simulated to compare dummy kinematics and dynamic responses in optimal restraint configurations. Results. Restraint misuse was associated with greater motion of the dummy torso and head during crashes, often allowing contact between the child and the vehicle interior, resulting in injury. Poor pre-crash posture for a child inappropriately restrained in an adult belt appeared to worsen the geometry of the sash (shoulder) belt, resulting in a cervical injury due to direct interaction with the belt. Dynamic dummy data did not appear to discriminate between injury and non-injury cases. Conclusions. Dummy kinematics suggest that injuries in which inappropriate use and misuse were a factor were less likely if the most appropriate restraint was used correctly. Adequately controlling the head and upper body of the child occupant was seen to prevent undesirable interactions with the vehicle interior and restraint system, which were associated with injury in the real world. Neck forces and moments and injury criteria calculated from these did not predict injury reliably.

Neuromuscular control of the head in an isometric force reproduction task: comparison of whiplash subjects and healthy controls

Background context A number of recent scientific publications suggest that patients suffering from whiplash-associated disorders (WADs) exhibit sensorimotor deficits in the control of head and neck movements. Purpose The main objective of the present study was to evaluate if subjects with WADs can produce isometric neck extension and flexion forces with precision, variability, and a mode of control similar to the values of healthy subjects. Study design A control group study with repeated measures. Patient samples Neck force production parameters and neuromuscular control were measured in 17 whiplash and 14 control subjects. The experimental group included subjects who had a history of persistent neck pain or disability after a motor vehicle accident. Outcome measures Pain levels were assessed on a standard 100-mm visual analog pain scale at the beginning and end of the experiment. Each whiplash subject completed the neck disability index and the short-form 36 health survey (SF-36) questionnaire before the experiment. Methods All subjects were asked to exert flexion and extension forces against a fixed head harness. Kinetic variables included time to peak force, time to peak force variability, peak force variability, and absolute error in peak force. Surface electrodes were applied bilaterally over the sternocleidomastoideus and paraspinal muscles. Electromyography (EMG)-dependent variables included EMG burst duration and amplitude using numerical integrated techniques. Results The average time to peak force was significantly longer for whiplash subjects than for the healthy controls. A significant increase in peak force variability was also observed in the whiplash group, and no group differences were noted for absolute error. Heightened muscular activity was seen in both paraspinal muscles, even though it only reached statistical significance for the left paraspinal muscle. Conclusion Our results show that the whiplash subjects involved in the study were able to produce isometric forces with spatial precision similar to healthy controls using a motor strategy in which the time to peak force is increased. This trade-off between spatial precision and time to peak force probably reflects an adaptation aimed at limiting pain and further injuries.

Neck injury tolerance under inertial loads in side impacts

Neck injury remains a major issue in road safety. Current side impact dummies and side impact crashworthiness assessments do not assess the risk of neck injury. These assessments are limited by biofidelity and knowledge regarding neck injury criteria and tolerance levels in side impacts. Side impact tests with PMHS were performed at the Heidelberg University in the 1980s and 1990s to improve primarily the understanding of trunk dynamics, injury mechanisms and criteria. In order to contribute to the definition of human tolerances at neck level, this study presents an analysis of the head/neck biomechanical parameters that were measured in these tests and their relationship to neck injury severity. Data from 15 impact tests were analysed. Head accelerations, and neck forces and moments were calculated from 9-accelerometer array head data, X-rays and anthropometric data. Statistically significant relationships were observed between resultant head acceleration and neck force and neck injury severity. The average resultant head acceleration for AIS 2 neck injuries was 112 g, while resultant neck force was 4925 N and moment 241 Nm. The data compared well to other test data on cadavers and volunteers. It is hoped that the paper will assist in the understanding of neck injuries and the development of tolerance criteria.

The effect of using universal anchorages in child restraint seats on the injury potential for children in frontal crash

This paper focuses on the efficacy of various methods used for anchoring child safety seats in vehicles. An experimental vehicle crash test was conducted incorporating two three-year-old Hybrid III crash test dummies, restrained in a five-point child restraint seats, in accordance to Canadian Motor Vehicle Safety Standard 208. One Child Restraint Seat was affixed to the vehicle seat using the car seat belt and the second was anchored using the lower anchorages provided in the vehicle for child seats. A top tether was used in addition to both the anchoring techniques to provide additional support to the child safety seat. The vehicle crash test was completed to investigate the head, neck, and thoracic injury potential of the Hybrid III crash test dummies due to change in anchoring methods. Similarities and differences were noted in the response of the two dummies to the same crash conditions. Peak values of the neck injury criteria, calculated from the observations obtained from the lower neck loads cell ranged from 1.7 to 1.9. The head injury criteria calculated over a 15 ms evaluation period were observed to lie between 250 and 350, and the values computed over a 36 ms evaluation period ranged between 450 and 600. Percentage reduction of approximately 10% to 20% was observed in the neck forces and moments and head accelerations by using the adult seat belt instead of the ISOFIX for CRS anchoring. A high probability of neck and cervical injuries was estimated for both child restraining configurations.

Effects of Initial Seated Position in Low Speed Rear-End Impacts: A Comparison with the TNO Rear Impact Dummy (TRID) Model

Injury-producing mechanisms associated with rear-end impact collision has remained a mystery not withstanding numerous investigations devoted to its scrutiny. Several criteria have been proposed to predict the injury-causing mechanism, but none have been universally accepted. The challenge lies in determining a set of testing procedures representative of real-world collisions, wherein the results obtained are not only the same as human testing, but remain consistent with various subjects and impact conditions. It is hypothesized that one of the most important considerations in the testing methodology is the effect of initial seated position (ISP) on occupant kinematics during a rear impact collision. This study involves two parts that evaluates the effects of ISP during rear-end impact. In the first part, head acceleration results of computer simulation using Hybrid III TNO rear impact dummy (TRID) are compared to physical impact testing (PIT) of humans. The second part focuses on the computer simulation using TRID to obtain different neck parameters such as NIC (Neck Injury Criterion), NIJ (Neck Injury Predictor), neck forces and moments to predict the level of neck injury such as whiplash associated disorder (WAD) during low speed rear-end impact. In PIT, a total of 17 rear-impact tests were conducted with a nominal 8-km/hour change in velocity to 5 subjects in four different seated positions comprising of a normal position (NP) and three out of positions (OOP). The first position was a NP, defined as torso against the seat back, looking straight ahead, hands on the steering wheel, and feet on the floor. The second position was a head flex position (HFP), defined as the normal position with head flexed forward approximately 20 degrees. The third position was a torso lean position (TLP), defined as the normal position with torso leaned forward approximately 10 degrees away from the seat back. Lastly, a torso lean head flex position (TLHFP), defined as the normal position with the head flexed forward approximately 20 degrees and torso leaned forward approximately 10 degrees. The head acceleration plots from PIT reveal that for the third and fourth positions (TLP and TLHFP) when the subject torso leaned forward, the peak head acceleration for the subject decreased and there was also a delay in reaching the peak. The Hybrid III-TRID anthropomorphic test dummy (ATD) was used in the same four different seated positions using computer simulation software MAthematical DYnamic MOdel (MADYMO 6.0) and the head acceleration results were compared to PIT. The comparison demonstrates that the Hybrid III-TRID ATD with MADYMO can be a reliable testing procedure during low-speed, rear-end impact for the four ISPs considered since the head acceleration plots deviated within the range of PIT head acceleration plots for different human subjects. This ensures that the second part of the study with neck injury using computer simulation results is a reliable testing procedure. It can be observed that MADYMO results have a greater error when compared to PIT when more than one OOP condition is employed as in TLHFP. All these observations would help in providing a tool to better understand the injury mechanisms and provide an accurate testing procedure for rear-end impact.

A study of injury parameters for rearward and forward facing 3-year-old child dummy using numerical simulation

More children die of road traffic injuries than of any other cause. Nonuse and misuse of child restraints is common and leads to preventable severe injuries or deaths. Furthermore, many children graduate to inappropriate restraint systems or switch from rearward to forward facing prematurely. Facing rearward is intrinsically safer, provided the head is supported, and the reasons for seating a child in the opposite position relate to convenience, not safety. With heavy heads and weak necks, children are vulnerable to catastrophic traction injuries to the cervical cord, and children older than 1 year retain this vulnerability. Most studies have estimated that rearward facing restraints reduce the risk of serious injury by about 80–90%. A recent analysis of the Swedish Volvo crash database reported that the injury reducing effect of rearward facing child restraints might be as high as 96%. However, the age at which children should start sitting in a forward-facing position is controversial. The American Academy of Pediatrics has recently advised that children should be seated facing the rear of the vehicle for as long as possible and at least until 1 year of age. Both Transport Canada and the US National Highway Traffic Safety Administration (NHTSA) currently suggest having children face forward from about 1 year of age or once they reach 10 kg (22 lb), while Australian children are often turned around to forward facing at 5 to 6 months of age. In this paper a multi-body dynamic simulation MADYMO model is developed for rearward and forward facing 3-year-old child dummy. The reasonable correlation between the developed forward facing numerical simulation results and the experimental results indicates that the model is robust. Simulation for both facing configurations is conducted using an experimental moderate frontal crash pulse. The study indicates that the upper neck forces, and the neck injury criteria can be greatly reduced by keeping the child in the rearward facing position. For children safety, parents and caregivers should seriously consider keeping children rearward facing for as long as possible. Moreover, manufacturers should be encouraged to develop car safety seats that accommodate children rear facing up to 4 years of age.

Neuromuscular Performance Characteristics of Open-Wheel and Rally Drivers

The purpose of the present study was to investigate neuromuscular performance characteristics in open-wheel and rally drivers using the cross-sectional study design. The subjects (N = 28) consisted of experienced international-level open-wheel drivers (n = 9), experienced international-level rally drivers (n = 9) and a physically active nondriving male control group (n = 10). In 3 separate test sessions, speed, muscle strength, and endurance tests were performed. The rally drivers had higher (p < 0.05) grip, shoulder flexion, and ankle plantar flexion strength, as compared to the control group. The open-wheel drivers showed higher strengths (p < 0.05) than the controls in neck forces, grip, shoulder flexion, and leg extension. The rally drivers were stronger (p < 0.05) than the open-wheel drivers in grip, plantar flexion, and trunk extension forces, whereas the open-wheel drivers were stronger (p < 0.01) than the rally drivers in neck lateral flexions and extension forces. Thus, competitive long-term open-wheel and rally drivers differ specifically in neuromuscular performance. For practice, these findings suggest that rally drivers should concentrate on training hand, ankle, and trunk muscles, whereas open-wheel drivers should train neck muscles, especially, and all other muscle groups rather equally.

Head–neck finite element model of the crash test dummy THOR

Development, calibration and validation of a three-dimensional finite element model of the head-neck sub-assemblies of the THOR 50th percentile male dummy are presented. The model provides, in conjunction with the use of the physical dummy, a computational tool for head-neck injury studies related to motor vehicle, rail, or aircraft crashes. Physical dummy CAD data is used to construct the finite element mesh. Mass and inertia properties of the model are consistent with those of the hardware. The THOR head spring-cable system, designed to produce a neck that gives more biofidelic head trajectories, is properly represented in the model. Several modelling methods are discussed in detail. The deformable components of the model include head skin (vinyl), face foam (Confor foam), face pad (silicone rubber), head springs, neck cables and neck discs (neoprene rubber). The material properties are determined, or calibrated, mainly from system identifications with data from material tests, head and face impact tests on a full dummy and sled tests on stand-alone head-neck sub-assemblies. The model is validated with the remaining sled test data and head-neck pendulum test data. Key simulation results such as head spring forces, motion trajectories, accelerations at head centre of gravity, and neck forces and moments are compared with the corresponding experimental data, and error analyses are conducted for the presented results.

Prediction of Cervical Spine Injury Risk for the 6-Year-Old Child in Frontal Crashes

This article presents a series of 49 km/h sled tests using the Hybrid III 6-year-old dummy in a high-back booster, a low-back booster, and a three-point belt. Although a 10-year review at a level I trauma center showed that noncontact cervical spine injuries are rare in correctly restrained booster-age children, dummy neck loads exceeded published injury thresholds in all tests. The dummy underwent extreme neck flexion during the test, causing full-face contact with the dummy's chest. These dummy kinematics were compared to the kinematics of a 12-year-old cadaver tested in a similar impact environment. The cadaver test showed neck flexion, but also significant thoracic spinal flexion which was nonexistent in the dummy. This comparison was expanded using MADYMO simulations in which the thoracic spinal stiffness of the dummy model was decreased to give a more biofidelic kinematic response. We conclude that the stiff thoracic spine of the dummy results in high neck forces and moments that are not representative of the true injury potential.

The influence of seatback characteristics on cervical injury risk in severe rear impacts

The determination of the optimum seatback characteristics for the mitigation of serious and catastrophic neck injury during high-speed rear-end collisions remains a topic of continued investigation. Despite a number of prior research efforts, both field data and sled test studies have yet to define a single optimal seatback performance criterion. Further, recent developments in seatbacks have introduced new designs into the field that have not been compared to more traditional designs. Analysis of NASS data from 1980 to 1999 demonstrated that at changes in velocity (Δ V) above 40 kph, rear-end collisions have a dramatically lower risk for catastrophic injury than frontal, near-side or far-side impacts. Unfortunately, owing to the small penetration of newer seatback designs in the automotive fleet, it is not possible to examine the influence of seatback design parameters on serious neck injury using these data alone. Accordingly, seven rear impact HYGE sled tests were conducted using a wide range of seat designs. Upper and lower neck load cells were used to measure neck forces and moments in restrained 50th male Hybrid III anthropomorphic test devices (ATD). Additionally, the neck injury criteria (Nij) was computed. Unlike prior studies that have examined the standard seated ATD or the dramatically out-of-position ATD, these tests were conducted using an ATD seated in non-standard but typical driving position. The results of this study indicate that several descriptions of seatback behavior, such as quasi-static ultimate force are poor predictors of ATD neck loading. It also suggests that, for the severe crash studied, an optimum range of seatback stiffness exists, which appears to be in the mid-range of seatback stiffnesses available in current production vehicles. These data continue to illustrate the complex relationship of seatback design parameters to neck injury risk.

Influence of crash severity and contact surfaces characteristics on the dynamic behavior of forward facing child occupants

The safety of children as occupants, in the event of vehicle collisions, is a pressing issue demanding more research and investigation to reduce harm and minimize injuries. Statistics show that motor vehicle crashes are the leading cause of death and injury for children, despite improved crashworthiness of vehicles and effective child restraint systems (CRS). Studies indicate that during a collision, children develop injury patterns, which are not fully understood. These child injury patterns are different from those experienced by adults due to differences in weight, height, and body proportions. Infants and young children have a disproportionately large head, with a high center of gravity and a weaker neck structure resulting in relatively poor head support. Vehicle speed, weight, impact mode (full-frontal, front offset, angled, side, or rear), type and location of the child restraint system and the interior design of the occupant compartment are some of the important factors that influence injury patterns and degree of harm in a child occupant. In this paper, a multi-body dynamic simulation model is developed, using MADYMO software, to investigate the behavior of a TNO-P3/4 9-month-old forward facing child dummy in a four-point convertible child safety seat. The reasonable correlation between the developed model simulations and experimental results from a CRABI 12-month child dummy sled test indicates that the model is robust. Simulations using three crash pulses, soft, moderate, and severe, are conducted to investigate the influence of crash severity on the child dummy head and thorax accelerations, upper neck forces, and injury parameters. The influence of contact surfaces characteristics is also investigated to shed some light on ways to improve child occupant kinematics during vehicle collisions. The study indicates that dynamic simulation is efficient, cost effective, and viable tool for vehicle occupant protection studies, policy change recommendations, and vehicle design modifications.

Influence of crash severity and contact surfaces characteristics on the dynamic behavior of forward facing child occupants

Abstract The safety of children as occupants, in the event of vehicle collisions, is a pressing issue demanding more research and investigation to reduce harm and minimize injuries. Statistics show that motor vehicle crashes are the leading cause of death and injury for children, despite improved crashworthiness of vehicles and effective child restraint systems (CRS). Studies indicate that during a collision, children develop injury patterns, which are not fully understood. These child injury patterns are different from those experienced by adults due to differences in weight, height, and body proportions. Infants and young children have a disproportionately large head, with a high center of gravity and a weaker neck structure resulting in relatively poor head support. Vehicle speed, weight, impact mode (full-frontal, front offset, angled, side, or rear), type and location of the child restraint system and the interior design of the occupant compartment are some of the important factors that influence injury patterns and degree of harm in a child occupant. In this paper, a multi-body dynamic simulation model is developed, using MADYMO software, to investigate the behavior of a TNO-P3/4 9-month-old forward facing child dummy in a four-point convertible child safety seat. The reasonable correlation between the developed model simulations and experimental results from a CRABI 12-month child dummy sled test indicates that the model is robust. Simulations using three crash pulses, soft, moderate, and severe, are conducted to investigate the influence of crash severity on the child dummy head and thorax accelerations, upper neck forces, and injury parameters. The influence of contact surfaces characteristics is also investigated to shed some light on ways to improve child occupant kinematics during vehicle collisions. The study indicates that dynamic simulation is efficient, cost effective, and viable tool for vehicle occupant protection studies, policy change recommendations, and vehicle design modifications.

Determination of head/neck loads during manoeuvring acceleration

: Neck injury risk can increase when aircrew wear head mounted equipment while exposed to +Gz-loads. The effects of added weight and change in centre-of-gravity were determined during a centrifuge study using an instrumented manikin at Brooks AFB, Texas. Data included centrifuge Gz, head acceleration (three axes), and head and C7-TI pitch moment, compressive and shear forces. Helicopter (0.5G/s at +1.75 and +4Gz) and tactical aircraft (2Gk and 6GIs from +4 to 12Gz) accelerations were simulated (5s plateau at each level). Effect of added weights (up to overall 2.7kg) were measured in the forward pitch and lateral planes and tested using ANOVA. Seven real helmet systems were also tested. Head Gx and Gy increased with increasing +Gz-load, head weight, as CG shifted in the forward pitch plane, and onset rate. Head Gz was greatest when weight was distributed laterally. The resultant head and neck force and moment increased with increasing weight, pitch angle, and +Gz load. Neck forces and moments were significantly larger than those measured in the head.

Surface friction in near-vertex head and neck impact increases risk of injury

A computational head–neck model was developed to test the hypothesis that increases in friction between the head and impact surface will increase head and neck injury risk during near-axial impact. The model consisted of rigid vertebrae interconnected by assemblies of nonlinear springs and dashpots, and a finite element shell model of the skull. For frictionless impact surfaces, the model reproduced the kinematics and kinetics observed in near-axial impacts to cadaveric head–neck specimens. Increases in the coefficient of friction between the head and impact surface over a range from 0.0 to 1.0 resulted in increases of up to 40, 113, 9.8, and 43% in peak post-buckled resultant neck forces, peak moment at the occiput-C1 joint, peak resultant head accelerations, and HIC values, respectively. The most dramatic increases in injury-predicting quantities occurred for COF increases from 0.0 to 0.2, while further COF increases above 0.5 generally produced only nominal changes. These data suggest that safety equipment and impact environments which minimize the friction between the head and impact surface may reduce the risk of head and neck injury in near-vertex head impact.