Evaluation of the head-helmet sliding properties in an impact test

On-Field Evaluation of Mouthpiece-and-Helmet-Mounted Sensor Data from Head Kinematics in Football

PURPOSE

Wearable sensors are used to measure head impact exposure in sports. The Head Impact Telemetry (HIT) System is a helmet-mounted system that has been commonly utilized to measure head impacts in American football. Advancements in sensor technology have fueled the development of alternative sensor methods such as instrumented mouthguards. The objective of this study was to compare peak magnitude measured from high school football athletes dually instrumented with the HIT System and a mouthpiece-based sensor system.

METHODS

Data was collected at all contact practices and competitions over a single season of spring football. Recorded events were observed and identified on video and paired using event timestamps. Paired events were further stratified by removing mouthpiece events with peak resultant linear acceleration below 10 g and events with contact to the facemask or body of athletes.

RESULTS

A total of 133 paired events were analyzed in the results. There was a median difference (mouthpiece subtracted from HIT System) in peak resultant linear and rotational acceleration for concurrently measured events of 7.3 g and 189 rad/s2. Greater magnitude events resulted in larger kinematic differences between sensors and a Bland Altman analysis found a mean bias of 8.8 g and 104 rad/s2, respectively.

CONCLUSION

If the mouthpiece-based sensor is considered close to truth, the results of this study are consistent with previous HIT System validation studies indicating low error on average but high scatter across individual events. Future researchers should be mindful of sensor limitations when comparing results collected using varying sensor technologies.

An Assessment of Sikh Turban's Head Protection in Bicycle Incident Scenarios

Due to religious tenets, Sikh population wear turbans and are exempted from wearing helmets in several countries. However, the extent of protection provided by turbans against head injuries during head impacts remains untested. One aim of this study was to provide the first-series data of turbans' protective performance under impact conditions that are representative of real-world bicycle incidents and compare it with the performance of bicycle helmets. Another aim was to suggest potential ways for improving turban's protective performance. We tested five different turbans, distinguished by two wrapping styles and two fabric materials with a size variation in one of the styles. A Hybrid III headform fitted with the turban was dropped onto a 45 degrees anvil at 6.3 m/s and head accelerations were measured. We found large difference in the performance of different turbans, with up to 59% difference in peak translational acceleration, 85% in peak rotational acceleration, and 45% in peak rotational velocity between the best and worst performing turbans. For the same turban, impact on the left and right sides of the head produced very different head kinematics, showing the effects of turban layering. Compared to unprotected head impacts, turbans considerably reduce head injury metrics. However, turbans produced higher values of peak linear and rotational accelerations in front and left impacts than bicycle helmets, except from one turban which produced lower peak head kinematics values in left impacts. In addition, turbans produced peak rotational velocities comparable with bicycle helmets, except from one turban which produced higher values. The impact locations tested here were covered with thick layers of turbans and they were impacted against flat anvils. Turbans may not provide much protection if impacts occur at regions covered with limited amount of fabric or if the impact is against non-flat anvils, which remain untested. Our analysis shows that turbans can be easily compressed and bottom out creating spikes in the headform's translational acceleration. In addition, the high friction between the turban and anvil surface leads to higher tangential force generating more rotational motion. Hence, in addition to improving the coverage of the head, particularly in the crown and rear locations, we propose two directions for turban improvement: (i) adding deformable materials within the turban layers to increase the impact duration and reduce the risk of bottoming out; (ii) reducing the friction between turban layers to reduce the transmission of rotational motion to the head. Overall, the study assessed Turbans' protection in cyclist head collisions, with a vision that the results of this study can guide further necessary improvements for advanced head protection for the Sikh community.

The Influence of Headform Friction and Inertial Properties on Oblique Impact Helmet Testing

Helmet-testing headforms replicate the human head impact response, allowing the assessment of helmet protection and injury risk. However, the industry uses three different headforms with varying inertial and friction properties making study comparisons difficult because these headforms have different inertial and friction properties that may affect their impact response. This study aimed to quantify the influence of headform coefficient of friction (COF) and inertial properties on oblique impact response. The static COF of each headform condition (EN960, Hybrid III, NOCSAE, Hybrid III with a skull cap, NOCSAE with a skull cap) was measured against the helmet lining material used in a KASK prototype helmet. Each headform condition was tested with the same helmet model at two speeds (4.8 & 7.3 m/s) and two primary orientations (y-axis and x-axis rotation) with 5 repetitions, totaling 100 tests. The influence of impact location, inertial properties, and friction on linear and rotational impact kinematics was investigated using a MANOVA, and type II sums of squares were used to determine how much variance in dependent variables friction and inertia accounted for. Our results show significant differences in impact response between headforms, with rotational head kinematics being more sensitive to differences in inertial rather than frictional properties. However, at high-speed impacts, linear head kinematics are more affected by changes in frictional properties rather than inertial properties. Helmet testing protocols should consider differences between headforms' inertial and frictional properties during interpretation. These results provide a framework for cross-comparative analysis between studies that use different headforms and headform modifiers.

Evaluating child helmet protection and testing standards: A study using PIPER child head models aged 1.5, 3, 6, and 18 years

The anatomy of children's heads is unique and distinct from adults, with smaller and softer skulls and unfused fontanels and sutures. Despite this, most current helmet testing standards for children use the same peak linear acceleration threshold as for adults. It is unclear whether this is reasonable and otherwise what thresholds should be. To answer these questions, helmet-protected head responses for different ages are needed which is however lacking today. In this study, we apply continuously scalable PIPER child head models of 1.5, 3, and 6 years old (YO), and an upgraded 18YO to study child helmet protection under extensive linear and oblique impacts. The results of this study reveal an age-dependence trend in both global kinematics and tissue response, with younger children experiencing higher levels of acceleration and velocity, as well as increased skull stress and brain strain. These findings indicate the need for better protection for younger children, suggesting that youth helmets should have a lower linear kinematic threshold, with a preliminary value of 150g for 1.5-year-old helmets. However, the results also show a different trend in rotational kinematics, indicating that the threshold of rotational velocity for a 1.5YO is similar to that for adults. The results also support the current use of small-sized adult headforms for testing child helmets before new child headforms are available.

Characterization of the skin-to-bone mechanical interaction on porcine scalp: A combined experimental and computational approach

Fasciae are soft tissues permitting a large but finite sliding between organs, but also between skin and its underlying elements. The contribution of fasciae has been seldomly reported in the literature, and is usually neglected or overly simplified within simulations. In the present contribution, we propose to use peeling tests in order to quantify the skin-to-bone interaction associated with a simple computational approach based on a geometrical modeling of the skin-to-bone interface. To this aim, a new experimental set up combined with a computational model to characterize the skin-to-bone interaction were proposed. The current work is devoted to the porcine scalp complex since it constitutes a common mechanical surrogate for the human scalp complex. The ad hoc computational approach and peeling set up were firstly evaluated on a validation material, before being used to characterize the skin-to-bone interaction within 6 porcine specimens harvested from the scalp. Our experimental setup allowed to measure the peeling response of porcine scalp, showing a three-regimes response including a plateau force. The computational approach satisfyingly reproduced the peeling response based uniquely on experimental-based parameters and on a discrete modeling of skin-to-bone interface. The presented methodology is a first attempt to propose a computationally efficient geometrically based model able to take into account the skin-to-bone interaction up to failure and corroborated by experimental data, and may be largely extended to the modeling of soft interactions between biological human tissues in the future.

Human Head and Helmet Interface Friction Coefficients with Biological Sex and Hair Property Comparisons

Dummy headforms used for impact testing have changed little over the years, and frictional characteristics are thought not to represent the human head accurately. The frictional interface between the helmet and head is an essential factor affecting impact response. However, few studies have evaluated the coefficient of friction (COF) between the human head and helmet surface. This study's objectives were to quantify the human head's static and dynamic COF and evaluate the effect of biological sex and hair properties. Seventy-four participants slid their heads along a piece of helmet foam backed by a fixed load cell at varying normal force levels. As normal force increased, static and dynamic human head COF decreased following power-law curves. At 80 N, the static COF is 0.32 (95% CI 0.30-0.34), and the dynamic friction coefficient is 0.27 (95% CI 0.26-0.28). Biological sex and hair properties were determined not to affect human head COF. The COFs between the head and helmet surface should be used to develop more biofidelic head impact testing methods, define boundary conditions for computer simulations, and aid decision-making for helmet designs.

In-Depth Bicycle Collision Reconstruction: From a Crash Helmet to Brain Injury Evaluation

Traumatic brain injury (TBI) is a prevalent injury among cyclists experiencing head collisions. In legal cases, reliable brain injury evaluation can be difficult and controversial as mild injuries cannot be diagnosed with conventional brain imaging methods. In such cases, accident reconstruction may be used to predict the risk of TBI. However, lack of collision details can render accident reconstruction nearly impossible. Here, we introduce a reconstruction method to evaluate the brain injury in a bicycle–vehicle collision using the crash helmet alone. Following a thorough inspection of the cyclist’s helmet, we identified a severe impact, a moderate impact and several scrapes, which helped us to determine the impact conditions. We used our helmet test rig and intact helmets identical to the cyclist’s helmet to replicate the damage seen on the cyclist’s helmet involved in the real-world collision. We performed both linear and oblique impacts, measured the translational and rotational kinematics of the head and predicted the strain and the strain rate across the brain using a computational head model. Our results proved the hypothesis that the cyclist sustained a severe impact followed by a moderate impact on the road surface. The estimated head accelerations and velocity (167 g, 40.7 rad/s and 13.2 krad/s2) and the brain strain and strain rate (0.541 and 415/s) confirmed that the severe impact was large enough to produce mild to moderate TBI. The method introduced in this study can guide future accident reconstructions, allowing for the evaluation of TBI using the crash helmet only.

Experimental evaluation of impact-resistant gloves using surrogate hands

Injuries to the hand and fingers with varying degrees of severity are widespread in industries such as mining and oil and gas production. This study presents the results of tests carried out to measure the impact performance for commonly used impact-resistant gloves (metacarpal gloves). Sets of surrogate hands made out of a 3D-printed skeletal structure and soft tissues represented by synthetic gel were manufactured and subjected to controlled impact tests. The calibration and validation of the surrogates were based on impact response data reported previously for cadaveric specimens. Calibrated surrogate hand specimens were tested to assess the impact protection of typical metacarpal gloves. Each type of metacarpal glove provided different levels of protection measured by the decrease in the peak impact reaction force and the fractures detected after the impacts. Results indicated that surrogate specimens suffered fractures in 77% and 33% of the impacts for unprotected and protected hands, respectively.

Neurotrauma Prevention Review: Improving Helmet Design and Implementation

Neurotrauma continues to contribute to significant mortality and disability. The need for better protective equipment is apparent. This review focuses on improved helmet design and the necessity for continued research. We start by highlighting current innovations in helmet design for sport and subsequent utilization in the lay community for construction. The current standards by sport and organization are summarized. We then address current standards within the military environment. The pathophysiology is discussed with emphasis on how helmets provide protection. As innovative designs emerge, protection against secondary injury becomes apparent. Much research is needed, but this focused paper is intended to serve as a catalyst for improvement in helmet design and implementation to provide more efficient and reliable neuroprotection across broad arenas.

Use of Brain Biomechanical Models for Monitoring Impact Exposure in Contact Sports

Head acceleration measurement sensors are now widely deployed in the field to monitor head kinematic exposure in contact sports. The wealth of impact kinematics data provides valuable, yet challenging, opportunities to study the biomechanical basis of mild traumatic brain injury (mTBI) and subconcussive kinematic exposure. Head impact kinematics are translated into brain mechanical responses through physics-based computational simulations using validated brain models to study the mechanisms of injury. First, this article reviews representative legacy and contemporary brain biomechanical models primarily used for blunt impact simulation. Then, it summarizes perspectives regarding the development and validation of these models, and discusses how simulation results can be interpreted to facilitate injury risk assessment and head acceleration exposure monitoring in the context of contact sports. Recommendations and consensus statements are presented on the use of validated brain models in conjunction with kinematic sensor data to understand the biomechanics of mTBI and subconcussion. Mainly, there is general consensus that validated brain models have strong potential to improve injury prediction and interpretation of subconcussive kinematic exposure over global head kinematics alone. Nevertheless, a major roadblock to this capability is the lack of sufficient data encompassing different sports, sex, age and other factors. The authors recommend further integration of sensor data and simulations with modern data science techniques to generate large datasets of exposures and predicted brain responses along with associated clinical findings. These efforts are anticipated to help better understand the biomechanical basis of mTBI and improve the effectiveness in monitoring kinematic exposure in contact sports for risk and injury mitigation purposes.

Impact Velocity Measurement Method Based on Trajectory and Impact Position

The impact velocity of falling weight is an instantaneous quantity. Currently, measurement of impact velocity relies on high-speed sensors to capture the moment of impact. The trajectory-position measurement method (TPMM) is proposed in this study. The main steps are: (1) The impact position is used to capture the impact time. It can be measured when the falling weight is stationary. (2) The discrete falling trajectory is measured and a new empirical regression algorithm is proposed to fit the expression of falling trajectory. (3) The impact velocity is obtained by taking the impact time into the first derivative of the trajectory expression. For 1-5 m falling height, the simulation shows that the relative maximum error and relative expanded uncertainty of the proposed method are less than 0.481% and 0.442%, respectively. Then, the actual experiment is carried out to verify the simulation. The proposed method has high accuracy and low uncertainty. The reasons are: (1) Only a low-speed displacement sensor is need for impact velocity measurement. It is easier to improve accuracy and stability of a low-speed sensor. (2) The empirical regression algorithm can improve the stability of falling trajectory fitting.

Consensus Head Acceleration Measurement Practices (CHAMP): Laboratory Validation of Wearable Head Kinematic Devices

Wearable devices are increasingly used to measure real-world head impacts and study brain injury mechanisms. These devices must undergo validation testing to ensure they provide reliable and accurate information for head impact sensing, and controlled laboratory testing should be the first step of validation. Past validation studies have applied varying methodologies, and some devices have been deployed for on-field use without validation. This paper presents best practices recommendations for validating wearable head kinematic devices in the laboratory, with the goal of standardizing validation test methods and data reporting. Key considerations, recommended approaches, and specific considerations were developed for four main aspects of laboratory validation, including surrogate selection, test conditions, data collection, and data analysis. Recommendations were generated by a group with expertise in head kinematic sensing and laboratory validation methods and reviewed by a larger group to achieve consensus on best practices. We recommend that these best practices are followed by manufacturers, users, and reviewers to conduct and/or review laboratory validation of wearable devices, which is a minimum initial step prior to on-field validation and deployment. We anticipate that the best practices recommendations will lead to more rigorous validation of wearable head kinematic devices and higher accuracy in head impact data, which can subsequently advance brain injury research and management.

Oblique impact responses of Hybrid III and a new headform with more biofidelic coefficient of friction and moments of inertia

New oblique impact methods for evaluating head injury mitigation effects of helmets are emerging, which mandate measuring both translational and rotational kinematics of the headform. These methods need headforms with biofidelic mass, moments of inertia (MoIs), and coefficient of friction (CoF). To fulfill this need, working group 11 of the European standardization head protection committee (CEN/TC158) has been working on the development of a new headform with realistic MoIs and CoF, based on recent biomechanics research on the human head. In this study, we used a version of this headform (Cellbond) to test a motorcycle helmet under the oblique impact at 8 m/s at five different locations. We also used the Hybrid III headform, which is commonly used in the helmet oblique impact. We tested whether there is a difference between the predictions of the headforms in terms of injury metrics based on head kinematics, including peak translational and rotational acceleration, peak rotational velocity, and BrIC (brain injury criterion). We also used the Imperial College finite element model of the human head to predict the strain and strain rate across the brain and tested whether there is a difference between the headforms in terms of the predicted strain and strain rate. We found that the Cellbond headform produced similar or higher peak translational accelerations depending on the impact location (−3.2% in the front-side impact to 24.3% in the rear impact). The Cellbond headform, however, produced significantly lower peak rotational acceleration (−41.8% in a rear impact to −62.7% in a side impact), peak rotational velocity (−29.5% in a side impact to −47.6% in a rear impact), and BrIC (−29% in a rear-side impact to −45.3% in a rear impact). The 90th percentile values of the maximum brain strain and strain rate were also significantly lower using this headform. Our results suggest that MoIs and CoF have significant effects on headform rotational kinematics, and consequently brain deformation, during the helmeted oblique impact. Future helmet standards and rating methods should use headforms with realistic MoIs and CoF (e.g., the Cellbond headform) to ensure more accurate representation of the head in laboratory impact tests.

Mechanical Characterization of Synthetic Gels for Creation of Surrogate Hands Subjected to Low-Velocity Impacts

The development of human body simulators that can be used as surrogates for testing protective devices and measures requires selecting synthetic materials with mechanical properties closely representative of the human tissues under consideration. For impact tests, gelatinous materials are often used to represent the soft tissues as a whole without distinguishing layers such as skin, fat, or muscles. This research focuses on the mechanical characterization of medical-grade synthetic gels that can be implemented to represent the soft tissues of the hand. Six grades of commercially available gels are selected for quasi-static hardness and firmness tests as well as for controlled low-velocity impact tests, which are not routinely conducted by gel manufacturers and require additional considerations such as energy level and specimen sizes relevant to the specific application. Specimens subject to impacts represent the hand thicknesses at the fingers, knuckles, and mid-metacarpal regions. Two impact test configurations are considered: one with the gel specimens including a solid insert representing a bone and one without this insert. The impact behavior of the candidate gels is evaluated by the coefficient of restitution, the energy loss percentage, and the peak reaction force at the time of impact. The resulting values are compared with similar indicators reported for experiments with cadaveric hands. Relatively softer gels, characterized by Shore OOO hardness in the range of 32.6 ± 0.9 to 34.4 ± 2.0, closely matched the impact behavior of cadaveric specimens. These results show that softer gels would be the most suitable gels to represent soft tissues in the creation of surrogate hands that can be used for extensive impact testing, thus, minimizing the need for cadaveric specimens.

The Effect of MIPS, Headform Condition, and Impact Orientation on Headform Kinematics Across a Range of Impact Speeds During Oblique Bicycle Helmet Impacts

Bicycle helmets are designed to attenuate both the linear and rotational response of the head during an oblique impact. Here we sought to quantify how the effectiveness of one popular rotation-attenuating system (MIPS) varied across 3 test headform conditions (bare, covered in stockings, and hair), 3 oblique impact orientations, and 4 impact speeds. We conducted 72 freefall drop tests of a single helmet model with and without MIPS onto a 45° angled anvil and measured the peak linear (PLA) and angular acceleration (PAA) and computed the angular velocity change (PAV) and brain injury criterion (BrIC). Across all headform conditions, MIPS reduced PAA and PAV by 38.2 and 33.2% respectively during X-axis rotation, 47.4 and 38.1% respectively during Y-axis rotation, and 22.9 and 20.5% during a combined ZY-axis rotation. Across all impact orientations, PAA was reduced by 39% and PAV by 32.4% with the bare headform while adding stockings reduced PAA and PAV by 41.6 and 36% respectively and the hair condition reduced PAA and PAV by 30.2 and 24.4% respectively. In addition, our data reveal the importance of using consistent headform conditions when evaluating the effect of helmet systems designed to attenuate head rotations during oblique impacts.

The Protective Performance of Modern Motorcycle Helmets Under Oblique Impacts

Motorcyclists are at high risk of head injuries, including skull fractures, focal brain injuries, intracranial bleeding and diffuse brain injuries. New helmet technologies have been developed to mitigate head injuries in motorcycle collisions, but there is limited information on their performance under commonly occurring oblique impacts. We used an oblique impact method to assess the performance of seven modern motorcycle helmets at five impact locations. Four helmets were fitted with rotational management technologies: a low friction layer (MIPS), three-layer liner system (Flex) and dampers-connected liner system (ODS). Helmets were dropped onto a 45° anvil at 8 m/s at five locations. We determined peak translational and rotational accelerations (PTA and PRA), peak rotational velocity (PRV) and brain injury criteria (BrIC). In addition, we used a human head finite element model to predict strain distribution across the brain and in corpus callosum and sulci. We found that the impact location affected the injury metrics and brain strain, but this effect was not consistent. The rear impact produced lowest PTAs but highest PRAs. This impact produced highest strain in corpus callosum. The front impact produced the highest PRV and BrIC. The side impact produced the lowest PRV, BrIC and strain across the brain, sulci and corpus callosum. Among helmet technologies, MIPS reduced all injury metrics and brain strain compared with conventional helmets. Flex however was effective in reducing PRA only and ODS was not effective in reducing any injury metrics in comparison with conventional helmets. This study shows the importance of using different impact locations and injury metrics when assessing head protection effects of helmets. It also provides new data on the performance of modern motorcycle helmets. These results can help with improving helmet design and standard and rating test methods.

Influence of Friction at the Head-Helmet Interface on Advanced Combat Helmet (ACH) Blunt Impact Kinematic Performance

INTRODUCTION

The purpose of this study was to compare the rotational blunt impact performance of an anthropomorphic test device (ATD: male 50% Hybrid III head and neck) headform donning an Advanced Combat Helmet (ACH) between conditions in which the coefficient of static friction (μs) at the head-to-helmet pad interface varied.

MATERIALS AND METHODS

Two ACHs (size large) were used in this study and friction was varied using polytetrafluoroethylene (PTFE), human hair, skullcap, and the native vinyl skin of the ATD. A condition in which hook and loop material adhered the headform to the liner system was also tested, resulting in a total of five conditions: PTFE, Human Hair, Skullcap, Vinyl, and Hook. Blunt impact tests with each helmet in each of the five conditions were conducted on a pneumatic linear impactor at 4.3 m/s. The ATD donning the ACH was impacted in seven locations (Crown, Front, Rear, Left Side, Right Side, Left Nape, and Right Nape). The peak resultant angular acceleration (PAA), velocity (PAV), and the Diffuse Axonal Multi-Axis, General Evaluation (DAMAGE) metric were compared between conditions.

RESULTS

No pairwise differences were observed between conditions for PAA. A positive correlation was observed between mean μs and PAA at the Front (τ = 0.28; P = .044) and Rear (τ = 0.31; P = .024) impact locations. The Hook condition had a mean PAV value that was often less than the other conditions (P ≤ .024). A positive correlation was observed between mean μs and PAV at the Front (τ = 0.32; P = .019) and Right Side (τ = 0.57; P < .001) locations. The Hook condition tended to have the lowest DAMAGE value compared to the other conditions (P ≤ .032). A positive correlation was observed between the mean μs and DAMAGE at the Rear (τ = 0.60; P < .001) location. A negative correlation was observed at the Left Side (τ = -0.28; P = .040), Right Side (τ = -0.58; P < .001) and Left Nape (τ = -0.56; P < .001) locations.

CONCLUSIONS

The results of this study indicate that at some impact locations kinematic responses can vary as a function of the friction at the head-to-helmet pad interface. However, a reduction in the coupling of the head-helmet pad interface did not consistently reduce head angular kinematics or measures of brain strain across impact locations. Thus, for the ACH during collision-type impacts, impact location as opposed to μs seems to have a greater influence on head kinematics and rotational-based measures of brain strain.

The Influence of Headform/Helmet Friction on Head Impact Biomechanics in Oblique Impacts at Different Tangential Velocities

Oblique impacts of the helmet against the ground are the most frequent scenarios in real-world motorcycle crashes. The combination of two factors that largely affect the results of oblique impact tests are discussed in this work. This study aims to quantify the effect of the friction at the interface between the headform and the interior of a motorcycle helmet at different magnitudes of tangential velocity. The helmeted headform, with low friction and high friction surface of the headform, was dropped against three oblique anvils at different impact velocities resulting in three different magnitudes of the tangential velocity (3.27 m/s, 5.66 m/s, 8.08 m/s) with the same normal component of the impact velocity (5.66 m/s). Three impact directions (front, left-side and right-side) and three repetitions per impact condition were tested resulting in 54 impacts. Tangential velocity variation showed little effect on the linear acceleration results. On the contrary, the rotational results showed that the effect of the headform’s surface depends on the magnitude of the tangential velocity and on the impact direction. These results indicate that a combination of low friction with low tangential velocities may result into underprediction of the rotational headform variables that would not be representative of real-world conditions.

Head Impact Telemetry System's Video-based Impact Detection and Location Accuracy

PURPOSE

This study aimed to quantify the Head Impact Telemetry (HIT) System's impact detection and location measurement accuracy using an impact biomechanics data set paired with video of high school football special teams plays.

METHODS

The head impact biomechanics data set and video were collected from 22 high school football players, wearing HIT System instrumented helmets, competing in 218 special teams plays over a single high school football season. We used two separate video analysis approaches. To quantify the impact detection accuracy, we evaluated the video for head impacts independently of the impact data collection triggers collected by the HIT System. Video-observed impacts matched to valid and invalid head impacts by the HIT System algorithm were categorized as true positives, false positives, false negatives, and true negatives. To quantify impact location accuracy, we analyzed video-synchronized head impacts for impact location independent of the HIT System's impact location measurement and quantified the estimated percent agreement of impact location between the HIT System recorded impact location and the impact location observed on video.

RESULTS

The HIT System's impact-filtering algorithm had 69% sensitivity, 72% specificity, and 70% accuracy in categorizing true and non-head impact data collection triggers. The HIT System agreed with video-observed impact locations on 64% of the 129 impacts we analyzed (unweighted k = 0.43, 95% confidence interval = 0.31-0.54).

CONCLUSION

This work provides data on the HIT System's impact detection and location accuracy during high school football special teams plays using game video analysis that has not been previously published. Based on our data, we believe that the HIT System is useful for estimating population-based impact location distributions for special teams plays.

A New Assessment of Bicycle Helmets: The Brain Injury Mitigation Effects of New Technologies in Oblique Impacts

New helmet technologies have been developed to improve the mitigation of traumatic brain injury (TBI) in bicycle accidents. However, their effectiveness under oblique impacts, which produce more strains in the brain in comparison with vertical impacts adopted by helmet standards, is still unclear. Here we used a new method to assess the brain injury prevention effects of 27 bicycle helmets in oblique impacts, including helmets fitted with a friction-reducing layer (MIPS), a shearing pad (SPIN), a wavy cellular liner (WaveCel), an airbag helmet (Hövding) and a number of conventional helmets. We tested whether helmets fitted with the new technologies can provide better brain protection than conventional helmets. Each helmeted headform was dropped onto a 45° inclined anvil at 6.3 m/s at three locations, with each impact location producing a dominant head rotation about one anatomical axes of the head. A detailed computational model of TBI was used to determine strain distribution across the brain and in key anatomical regions, the corpus callosum and sulci. Our results show that, in comparison with conventional helmets, the majority of helmets incorporating new technologies significantly reduced peak rotational acceleration and velocity and maximal strain in corpus callosum and sulci. Only one helmet with MIPS significantly increased strain in the corpus collosum. The helmets fitted with MIPS and WaveCel were more effective in reducing strain in impacts producing sagittal rotations and a helmet fitted with SPIN in coronal rotations. The airbag helmet was effective in reducing brain strain in all impacts, however, peak rotational velocity and brain strain heavily depended on the analysis time. These results suggest that incorporating different impact locations in future oblique impact test methods and designing helmet technologies for the mitigation of head rotation in different planes are key to reducing brain injuries in bicycle accidents.

Impact Performance Comparison of Advanced Snow Sport Helmets with Dedicated Rotation-Damping Systems

Rotational acceleration of the head is a principal cause of concussion and traumatic brain injury. Several rotation-damping systems for helmets have been introduced to better protect the brain from rotational forces. But these systems have not been evaluated in snow sport helmets. This study investigated two snow sport helmets with different rotation-damping systems, termed MIPS and WaveCel, in comparison to a standard snow sport helmet without a rotation-damping system. Impact performance was evaluated by vertical drops of a helmeted Hybrid III head and neck onto an oblique anvil. Six impact conditions were tested, comprising two impact speeds of 4.8 and 6.2 m/s, and three impact locations. Helmet performance was quantified in terms of the linear and rotational kinematics, and the predicted probability of concussion. Both rotation-damping systems significantly reduced rotational acceleration under all six impact conditions compared to the standard helmet, but their effect on linear acceleration was less consistent. The highest probability of concussion for the standard helmet was 89%, while helmets with MIPS and WaveCel systems exhibited a maximal probability of concussion of 67 and 7%, respectively. In conclusion, rotation-damping systems of advanced snow sport helmets can significantly reduce rotational head acceleration and the associated concussion risk.

The effect of the scalp on the effectiveness of bicycle helmets' anti-rotational acceleration technologies

OBJECTIVE

Medical data has lead to the common understanding that bicycle helmets need to be improved to better protect against brain injuries resulting from rotational acceleration. Although many different technologies exist for reducing rotational acceleration during impacts, the lack of an official testing standard means that their evaluation is based on customized set-ups that may differ and not represent real accident conditions. Previously, the authors have shown that scalp tissue plays an important role during helmet testing by absorbing energy and creating a low friction interface between head and helmet, thus reducing rotational accelerations and velocities. However, no published study has yet examined the effectiveness of anti-rotational helmet technologies in the presence of a biofidelic scalp layer. The objective of this study is to address this gap.

METHODS

Three different commercially available helmet models, each one equipped with a different technology, were tested in the presence of scalp tissue, in two different scenarios; with and without the technology present. The effectiveness of each of these technologies is already documented in other studies, but only in the absence of a biofidelic scalp layer. Tests were carried out using HIII headform with porcine scalp attached to the outmost layer. Motion tracking was used to compare the impact kinematics of each helmet model in both scenarios.

RESULTS

Results showed that when a biofidelic scalp layer is present, there is no statistical difference between helmet models with and without the anti-rotational technology in terms of rotational acceleration, velocity, relative rotation, impact duration and injury risk.

CONCLUSIONS

Results suggest that the presence of the scalp can obscure the functionality of anti-rotational acceleration technologies. This could indicate that the effectiveness of technologies tested in previous studies, which have not tested anti-rotational acceleration technologies in the presence of a realistic scalp layer, may exaggerate the contribution of such technologies if compared with a more biofidelic set-up. The study supports the fact that headforms should be better designed by incorporating artificial skin layers that can better imitate scalp's behavior and, in addition, provides insights for the design of technologies against rotational acceleration.

Mechanical Characterization and Modeling of the Porcine Cerebral Meninges

The cerebral meninges, made up of the dura, arachnoid, and pia mater, is a tri-layer membrane that surrounds the brain and the spinal cord and has an important function in protecting the brain from injury. Understanding its mechanical behavior is important to ensure the accuracy of finite element (FE) head model simulations which are commonly used in the study of traumatic brain injury (TBI). Mechanical characterization of freshly excised porcine dura-arachnoid mater (DAM) was achieved using uniaxial tensile testing and bulge inflation testing, highlighting the dependency of the identified parameters on the testing method. Experimental data was fit to the Ogden hyperelastic material model with best fit material parameters of μ = 450 ± 190 kPa and α = 16.55 ± 3.16 for uniaxial testing, and μ = 234 ± 193 kPa and α = 8.19 ± 3.29 for bulge inflation testing. The average ultimate tensile strength of the DAM was 6.91 ± 2.00 MPa (uniaxial), and the rupture stress at burst was 2.08 ± 0.41 MPa (inflation). A structural analysis using small angle light scattering (SALS) revealed that while local regions of highly aligned fibers exist, globally, there is no preferred orientation of fibers and the cerebral DAM can be considered to be structurally isotropic. This confirms the results of the uniaxial mechanical testing which found that there was no statistical difference between samples tested in the longitudinal and transversal direction (p = 0.13 for μ, p = 0.87 for α). A finite element simulation of a craniotomy procedure following brain swelling revealed that the mechanical properties of the meninges are important for predicting accurate stress and strain fields in the brain and meninges. Indeed, a simulation using a common linear elastic representation of the meninges was compared to the present material properties (Ogden model) and the intracranial pressure was found to differ by a factor of 3. The current study has provided researchers with primary experimental data on the mechanical behavior of the meninges which will further improve the accuracy of FE head models used in TBI.

An Evidence Basis for Future Equestrian Helmet Lateral Crush Certification Tests

The aim of this study is to determine what loads are likely to be applied to the head in the event of a horse falling onto it and to determine by how much a typical equestrian helmet reduces these loads. An instrumented headform was designed and built to measure applied dynamic loads from a falling horse. Two differently weighted equine cadavers were then dropped repeatedly from a height of 1 m (theoretical impact velocity of 4.43 m/s) onto both the un-helmeted and helmeted instrumented headforms to collect primary force–time history data. The highest mean peak loads applied to the headform by the lighter horse were measured at the bony sacral impact location (15.57 kN ± 1.11 SD). The lowest mean peak loads were measured at the relatively fleshier right hind quarter (7.91 kN ± 1.84 SD). For the heavier horse, highest mean peak loads applied to the headform were measured at the same bony sacral impact location (16.02 kN ± 0.83 SD), whilst lowest mean peak loads were measured at the more compliant left hind quarter (10.47 kN ± 1.08 SD). When compared with the un-helmeted mean values, a reduction of 29.7% was recorded for the sacral impact location and a reduction of 43.3% for the lumbosacral junction location for helmeted tests. Notably, all measured loads were within or exceeded the range of published data for the fracture of the adult lateral skull bone. Current helmet certification tests are not biofidelic and inadequately represent the loading conditions of real-world “lateral crush” accidents sustained in equestrian sports. This work presents the first ever evidence basis upon which any future changes to a certification standards test method might be established, thereby ensuring that such a test would be both useful, biofidelic, and could ensure the desired safety outcome.

High-speed helmeted head impacts in motorcycling: A computational study

The motorcyclist is exposed to the risk of falling and impacting ground head-first at a wide range of travelling speeds - from a speed limit of less than 50 km/h on the urban road to the race circuit where speed can reach well above 200 km/h. However, motorcycle helmets today are tested at a single and much lower impact speed, i.e. 30 km/h. There is a knowledge gap in understanding the dynamics and head impact responses at high travelling speeds due to the limitation of existing laboratory rigs. This study used a finite element head model coupled with a motorcycle helmet model to simulate head-first falls at travelling speed (or tangential velocity at impact) from 0 to 216 km/h. The effect of different falling heights (1.6 m and 0.25 m) and coefficient of frictions (0.20 and 0.45) between the helmet outer shell and ground were also examined. The simulation results were analysed together with the analytical model to better comprehend rolling and/or sliding phenomena that are often observed in helmet oblique impacts. Three types of helmet-to-ground interactions are found when the helmet impacts ground from low to high tangential velocities: (1) helmet rolling without slipping; (2) a combination of sliding and rolling; and (3) continuous sliding. The tangential impulse transmitted to the head-helmet system, peak angular head kinematics and brain strain increase almost linearly with the tangential velocity when the helmet rolls but plateaus when the helmet slides. The critical tangential velocity at which the motion transit from the rolling regime to the sliding regime depends on both the falling height and friction coefficient. Typically, for a fall height of 1.63 m and a friction coefficient of 0.45, the rolling/sliding transition occurs at a tangential velocity of 10.8 m/s (38.9 km/h). Low sliding resistance in helmet design, i.e. by the means of a lower friction coefficient between the helmet outer shell and ground, has shown a higher reduction of brain tissue strain in the sliding regime than in the rolling regime. This study uncovers the underlying dynamics of rolling and sliding phenomena in high-speed oblique impacts, which largely affect head impact biomechanics. Besides, the study highlights the importance of testing helmets at speeds covering both the rolling and sliding regime since potential designs for improved head protection at high-speed impacts can be more distinguishable in the sliding regime than in the rolling regime.

Impact Performance Comparison of Advanced Bicycle Helmets with Dedicated Rotation-Damping Systems

Bicycle helmets effectively mitigate skull fractures, but there is increasing concern on their effectiveness in mitigating traumatic brain injury (TBI) caused by rotational head acceleration. Bicycle falls typically involve oblique impacts that induce rotational head acceleration. Recently, bicycle helmet with dedicated rotation-damping systems have been introduced to mitigate rotational head acceleration. This study investigated the impact performance of four helmets with different rotation-damping systems in comparison to a standard bicycle helmet without a rotation-damping system. Impact performance was tested under oblique impact conditions by vertical drops of a helmeted headform onto an oblique anvil at 6.2 m/s impact speed. Helmet performance was quantified in terms of headform kinematics, corresponding TBI risk, and resulting brain strain. Of the four rotation-damping systems, two systems significantly reduced rotational head acceleration, TBI risk, and brain strain compared to the standard bicycle helmet. One system had no significant effect on impact performance compared to control helmets, and one system significantly increase linear and rotational head acceleration by 62 and 61%, respectively. In conclusion, results revealed significant differences in the effectiveness between rotation-damping systems, whereby some rotation-damping systems significantly reduced rotational head acceleration and associated TBI risk.

A review of impact testing methods for headgear in sports: Considerations for improved prevention of head injury through research and standards

Standards for sports headgear were introduced as far back as the 1960s and many have remained substantially unchanged to present day. Since this time, headgear has virtually eliminated catastrophic head injuries such as skull fractures and changed the landscape of head injuries in sports. Mild traumatic brain injury (mTBI) is now a prevalent concern and the effectiveness of headgear in mitigating mTBI is inconclusive for most sports. Given that most current headgear standards are confined to attenuating linear head mechanics and recent brain injury studies have underscored the importance of angular mechanics in the genesis of mTBI, new or expanded standards are needed to foster headgear development and assess headgear performance that addresses all types of sport-related head and brain injuries. The aim of this review is to provide a basis for developing new sports headgear impact tests for standards by summarizing and critiquing: 1) impact testing procedures currently codified in published headgear standards for sports and 2) new or proposed headgear impact test procedures in published literature and/or relevant conferences. Research areas identified as needing further knowledge to support standards test development include defining sports-specific head impact conditions, establishing injury and age appropriate headgear assessment criteria, and the development of headgear specific head and neck surrogates for at-risk populations.