Finite element modelling of equestrian helmet impacts exposes the need to address rotational kinematics in future helmet designs

Jockey head injuries, especially concussions, are common in horse racing. Current helmets do help to reduce the severity and incidences of head injury, but the high concussion incidence rates suggest that there may be scope to improve the performance of equestrian helmets. Finite element simulations in ABAQUS/Explicit were used to model a realistic helmet model during standard helmeted rigid headform impacts and helmeted head model University College Dublin Brain Trauma Model (UCDBTM) impacts.

Current helmet standards for impact determine helmet performance based solely on linear acceleration. Brain injury-related values (stress and strain) from the UCDBTM showed that a performance improvement based on linear acceleration does not imply the same improvement in head injury-related brain tissue loads. It is recommended that angular kinematics be considered in future equestrian helmet standards, as angular acceleration was seen to correlate with stress and strain in the brain.     

On the accuracy of the Head Impact Telemetry (HIT) System used in football helmets

On-field measurement of head impacts has relied on the Head Impact Telemetry (HIT) System, which uses helmet mounted accelerometers to determine linear and angular head accelerations. HIT is used in youth and collegiate football to assess the frequency and severity of helmet impacts. This paper evaluates the accuracy of HIT for individual head impacts. Most HIT validations used a medium helmet on a Hybrid III head. However, the appropriate helmet is large based on the Hybrid III head circumference (58 cm) and manufacturer's fitting instructions. An instrumented skull cap was used to measure the pressure between the head of football players (n=63) and their helmet. The average pressure with a large helmet on the Hybrid III was comparable to the average pressure from helmets used by players. A medium helmet on the Hybrid III produced average pressures greater than the 99th percentile volunteer pressure level. Linear impactor tests were conducted using a large and medium helmet on the Hybrid III. Testing was conducted by two independent laboratories. HIT data were compared to data from the Hybrid III equipped with a 3-2-2-2 accelerometer array. The absolute and root mean square error (RMSE) for HIT were computed for each impact (n=90). Fifty-five percent (n=49) had an absolute error greater than 15% while the RMSE was 59.1% for peak linear acceleration.     

A computational study of the EN 1078 impact test for bicycle helmets using a realistic subject-specific finite element head model

Abstract

In the present study, the free fall impact test in accordance with the EN1078 standard for certification of bicycle helmets is replicated using numerical simulations. The impact scenario is simulated using an experimentally validated, patient-specific head model equipped with and without a bicycle helmet. Head accelerations and intracranial biomechanical injury metrics during the impacts are recorded. It is demonstrated that wearing the bicycle helmet during the impact reduces biomechanical injury metrics, with the biggest reduction seen in the metric for skull fracture.     

Evaluation of the protective capacity of baseball helmets for concussive impacts

The purpose of this research was to examine how four different types of baseball helmets perform for baseball impacts when performance was measured using variables associated with concussion. A helmeted Hybrid III headform was impacted by a baseball, and linear and rotational acceleration as well as maximum principal strain were measured for each impact condition. The method was successful in distinguishing differences in design characteristics between the baseball helmets. The results indicated that there is a high risk of concussive injury from being hit by a ball regardless of helmet worn.     

A centric/non-centric impact protocol and finite element model methodology for the evaluation of American football helmets to evaluate risk of concussion

American football reports high incidences of head injuries, in particular, concussion. Research has described concussion as primarily a rotation dominant injury affecting the diffuse areas of brain tissue. Current standards do not measure how helmets manage rotational acceleration or how acceleration loading curves influence brain deformation from an impact and thus are missing important information in terms of how concussions occur. The purpose of this study was to investigate a proposed three-dimensional impact protocol for use in evaluating football helmets. The dynamic responses resulting from centric and non-centric impact conditions were examined to ascertain the influence they have on brain deformations in different functional regions of the brain that are linked to concussive symptoms. A centric and non-centric protocol was used to impact an American football helmet; the resulting dynamic response data was used in conjunction with a three-dimensional finite element analysis of the human brain to calculate brain tissue deformation. The direction of impact created unique loading conditions, resulting in peaks in different regions of the brain associated with concussive symptoms. The linear and rotational accelerations were not predictive of the brain deformation metrics used in this study. In conclusion, the test protocol used in this study revealed that impact conditions influences the region of loading in functional regions of brain tissue that are associated with the symptoms of concussion. The protocol also demonstrated that using brain deformation metrics may be more appropriate when evaluating risk of concussion than using dynamic response data alone.     

The influence of impact force redistribution and redirection on maximum principal strain for helmeted head impacts

Abstract

Sporting helmets with linear attenuating strategies are proficient at reducing the risk of traumatic brain injury. However, the continued high incidence of concussion in American football, has led researchers to investigate novel helmet liner strategies. These strategies typically supplement existing technologies by adding or integrating head-helmet decoupling mechanisms. Decoupling strategies aim to redirect or redistribute impact force around the head, reducing impact energy transferred to the brain. This results in decreased brain tissue strain, which is beneficial in injury risk reduction due to the link between tissue strain and concussive injury.

The purpose of this study was to mathematically demonstrate the effect of ten cases, representing theoretical redirection and redistribution helmet liner strategies, on brain tissue strain resulting from impacts to the head. The kinematic response data from twenty head impacts collected in the laboratory was mathematically modified to represent the altered response of the ten different cases and used as input parameters to determine the effect on maximum principal strain (MPS) values, calculated using finite element modeling. The results showed that a reduced dominant coordinate component (contributes the greatest to resultant) of rotational acceleration decreased maximum principal strain in American football helmets. The study theoretically demonstrates that liner strategies, if applied correctly, can influence brain motion, reduce brain tissue strain, and could decrease injury risk in an American football helmet.     

A six degree of freedom head acceleration measurement device for use in football

The high incidence rate of concussions in football provides a unique opportunity to collect biomechanical data to characterize mild traumatic brain injury. The goal of this study was to validate a six degree of freedom (6DOF) measurement device with 12 single-axis accelerometers that uses a novel algorithm to compute linear and angular head accelerations for each axis of the head. The 6DOF device can be integrated into existing football helmets and is capable of wireless data transmission. A football helmet equipped with the 6DOF device was fitted to a Hybrid III head instrumented with a 9 accelerometer array. The helmet was impacted using a pneumatic linear impactor. Hybrid III head accelerations were compared with that of the 6DOF device. For all impacts, peak Hybrid III head accelerations ranged from 24 g to 176 g and 1,506 rad/s(2) to 14,431 rad/s(2). Average errors for peak linear and angular head acceleration were 1% ± 18% and 3% ± 24%, respectively. The average RMS error of the temporal response for each impact was 12.5 g and 907 rad/s(2).     

Head impact exposure in collegiate football players

In American football, impacts to the helmet and the resulting head accelerations are the primary cause of concussion injury and potentially chronic brain injury. The purpose of this study was to quantify exposures to impacts to the head (frequency, location and magnitude) for individual collegiate football players and to investigate differences in head impact exposure by player position. A total of 314 players were enrolled at three institutions and 286,636 head impacts were recorded over three seasons. The 95th percentile peak linear and rotational acceleration and HITsp (a composite severity measure) were 62.7g, 4378rad/s(2) and 32.6, respectively. These exposure measures as well as the frequency of impacts varied significantly by player position and by helmet impact location. Running backs (RB) and quarter backs (QB) received the greatest magnitude head impacts, while defensive line (DL), offensive line (OL) and line backers (LB) received the most frequent head impacts (more than twice as many than any other position). Impacts to the top of the helmet had the lowest peak rotational acceleration (2387rad/s(2)), but the greatest peak linear acceleration (72.4g), and were the least frequent of all locations (13.7%) among all positions. OL and QB had the highest (49.2%) and the lowest (23.7%) frequency, respectively, of front impacts. QB received the greatest magnitude (70.8g and 5428rad/s(2)) and the most frequent (44% and 38.9%) impacts to the back of the helmet. This study quantified head impact exposure in collegiate football, providing data that is critical to advancing the understanding of the biomechanics of concussive injuries and sub-concussive head impacts.     

Rebreathing in a subject wearing an integral crash helmet.

The respired air of a volunteer was analysed while he was wearing a variety of integral crash helmets. Observations were made with and without a protective balaclava, bib or scarf, or both. Rebreathing occurred and the peak inspired oxygen tension fell as low as 16.0 kPa (120 mm Hg) with a minimum inspired carbon dioxide of 2.1 KPa (16.0 mm Hg). Accessories worn or attached to the helmet which restrict airflow into the helmet should not be used. Attention should be paid to the "air conditioning" of helmets when worn with flameproof balaclavas and bibs.     

Impact attenuation of male and female lacrosse helmets using a modal impulse hammer

It has been established that substantial negative changes in neurocognitive function can be observed in a large percentage of athletes who participate in contact sports such as soccer or football, motivating a need for improved safety systems. Head accelerations in men’s lacrosse are similar to those in football and female lacrosse players experience high rates of concussions, necessitating better head protection in both sports. Previous studies have sought to evaluate the ability of modern football helmets to mitigate impacts both normal and oblique to the surface of the helmet using a system that quantifies both the input load and the resulting accelerations of a Hybrid III headform. This study quantifies the inputs and outputs of the helmet-Hybrid III headform system in order to compare the impact attenuation capability of two male and two female lacrosse helmets. Of those helmets tested, the better performing male helmet was the Schutt Stallion 650 and the better performing female helmet was the Hummingbird excepting device failure at the rear boss impact location, but football helmets still generally outperformed the lacrosse helmets tested here.     

Simulation-based assessment for construction helmets

In recent years, there has been a concerted effort for greater job safety in all industries. Personnel protective equipment (PPE) has been developed to help mitigate the risk of injury to humans that might be exposed to hazardous situations. The human head is the most vulnerable to impact as a moderate magnitude can cause serious injury or death. That is why industries have required the use of an industrial hard hat or helmet. There have only been a few articles published to date that are focused on the risk of head injury when wearing an industrial helmet. A full understanding of the effectiveness of construction helmets on reducing injury is lacking. This paper presents a simulation-based method to determine the threshold at which a human will sustain injury when wearing a construction helmet and assesses the risk of injury for wearers of construction helmets or hard hats. Advanced finite element, or FE, models were developed to study the impact on construction helmets. The FE model consists of two parts: the helmet and the human models. The human model consists of a brain, enclosed by a skull and an outer layer of skin. The level and probability of injury to the head was determined using both the head injury criterion (HIC) and tolerance limits set by Deck and Willinger. The HIC has been widely used to assess the likelihood of head injury in vehicles. The tolerance levels proposed by Deck and Willinger are more suited for finite element models but lack wide-scale validation. Different cases of impact were studied using LSTC's LS-DYNA.     

Towards reducing impact-induced brain injury: lessons from a computational study of army and football helmet pads

We use computational simulations to compare the impact response of different football and U.S. Army helmet pad materials. We conduct experiments to characterise the material response of different helmet pads. We simulate experimental helmet impact tests performed by the U.S. Army to validate our methods. We then simulate a cylindrical impactor striking different pads. The acceleration history of the impactor is used to calculate the head injury criterion for each pad. We conduct sensitivity studies exploring the effects of pad composition, geometry and material stiffness. We find that (1) the football pad materials do not outperform the currently used military pad material in militarily relevant impact scenarios; (2) optimal material properties for a pad depend on impact energy and (3) thicker pads perform better at all velocities. Although we considered only the isolated response of pad materials, not entire helmet systems, our analysis suggests that by using larger helmet shells with correspondingly thicker pads, impact-induced traumatic brain injury may be reduced.     

Extreme helmet formation in Daphnia cucullata induced by small-scale turbulence

Although Daphnia cucullata is used as a textbook example forcyclomorphosis, distinct helmet development, as shown in thefield, has not been demonstrated in the laboratory until now.We show for the first time that small-scale turbulence is ableto induce the maximum response of morphological plasticity inD. cucullata. Helmet elongation reached magnitudes as extremeas observed in the field. Different modes of generating small-scaleturbulence caused different levels of helmet formation. Small-scaleturbulence alone may not be responsible for cyclomorphosis innature because field data show that two nearby lakes with similarmorphometry differ in cyclomorphosis patterns, while laboratoryexperiments show that there is no difference in the abilityto form helmets in the clones of each lake. Although helmetformation in D. cucullata is inducible with predator kairomones,helmet elongation is not as strong as that induced by turbulence.We discuss the possible role of helmets under turbulent conditions.     

Magnitude of head impact exposures in individual collegiate football players

The purpose of this study was to quantify the severity of head impacts sustained by individual collegiate football players and to investigate differences between impacts sustained during practice and game sessions, as well as by player position and impact location. Head impacts (N = 184,358) were analyzed for 254 collegiate players at three collegiate institutions. In practice, the 50th and 95th percentile values for individual players were 20.0 g and 49.5 g for peak linear acceleration, 1187 rad/s2 and 3147 rad/s2 for peak rotational acceleration, and 13.4 and 29.9 for HITsp, respectively. Only the 95th percentile HITsp increased significantly in games compared with practices (8.4%, p = .0002). Player position and impact location were the largest factors associated with differences in head impacts. Running backs consistently sustained the greatest impact magnitudes. Peak linear accelerations were greatest for impacts to the top of the helmet, whereas rotational accelerations were greatest for impacts to the front and back. The findings of this study provide essential data for future investigations that aim to establish the correlations between head impact exposure, acute brain injury, and long-term cognitive deficits.     

Protective capacity of an ice hockey goaltender helmet for three events associated with concussion

The purpose of this study was to assess the protective capacity of an ice hockey goaltender helmet for three concussive impact events. A helmeted and unhelmeted headform was used to test three common impact events in ice hockey (fall, puck impacts and shoulder collisions). Peak linear acceleration, rotational acceleration and rotational velocity as well as maximum principal strain and von Mises stress were measured for each impact condition. The results demonstrated the tested ice hockey goaltender helmet was well designed to manage fall and puck impacts but does not consistently protect against shoulder collisions and an opportunity may exist to improve helmet designs to better protect goaltenders from shoulder collisions.     

Brain tissue analysis of impacts to American football helmets

Concussion in American football is a prevalent concern. Research has been conducted examining frequencies, location, and thresholds for concussion from impacts. Little work has been done examining how impact location may affect risk of concussive injury. The purpose of this research was to examine how impact site on the helmet and type of impact, affects the risk of concussive injury as quantified using finite element modelling of the human head and brain. A linear impactor was used to impact a helmeted Hybrid III headform in several locations and using centric and non-centric impact vectors. The resulting dynamic response was used as input for the Wayne State Brain Injury Model to determine the risk of concussive injury by utilizing maximum principal strain as the predictive variable. The results demonstrated that impacts that occur primarily to the side of the head resulted in higher magnitudes of strain in the grey and white matter, as well as the brain stem. Finally, commonly worn American football helmets were used in this research and significant risk of injury was incurred for all impacts. These results suggest that improvements in American football helmets are warranted, in particular for impacts to the side of the helmet.     

Investigating helmet promotion for cyclists: results from a randomised study with observation of behaviour, using a semi-automatic video system

Introduction

Half of fatal injuries among bicyclists are head injuries. While helmet use is likely to provide protection, their use often remains rare. We assessed the influence of strategies for promotion of helmet use with direct observation of behaviour by a semi-automatic video system.

Methods

We performed a single-centre randomised controlled study, with 4 balanced randomisation groups. Participants were non-helmet users, aged 18–75 years, recruited at a loan facility in the city of Bordeaux, France. After completing a questionnaire investigating their attitudes towards road safety and helmet use, participants were randomly assigned to three groups with the provision of “helmet only”, “helmet and information” or “information only”, and to a fourth control group. Bikes were labelled with a colour code designed to enable observation of helmet use by participants while cycling, using a 7-spot semi-automatic video system located in the city. A total of 1557 participants were included in the study.

Results

Between October 15th 2009 and September 28th 2010, 2621 cyclists'' movements, made by 587 participants, were captured by the video system. Participants seen at least once with a helmet amounted to 6.6% of all observed participants, with higher rates in the two groups that received a helmet at baseline. The likelihood of observed helmet use was significantly increased among participants of the “helmet only” group (OR = 7.73 [2.09–28.5]) and this impact faded within six months following the intervention. No effect of information delivery was found.

Conclusion

Providing a helmet may be of value, but will not be sufficient to achieve high rates of helmet wearing among adult cyclists. Integrated and repeated prevention programmes will be needed, including free provision of helmets, but also information on the protective effect of helmets and strategies to increase peer and parental pressure.     

Finite element modeling of human brain response to football helmet impacts

The football helmet is used to help mitigate the occurrence of impact-related traumatic (TBI) and minor traumatic brain injuries (mTBI) in the game of American football. While the current helmet design methodology may be adequate for reducing linear acceleration of the head and minimizing TBI, it however has had less effect in minimizing mTBI. The objectives of this study are (a) to develop and validate a coupled finite element (FE) model of a football helmet and the human body, and (b) to assess responses of different regions of the brain to two different impact conditions – frontal oblique and crown impact conditions. The FE helmet model was validated using experimental results of drop tests. Subsequently, the integrated helmet–human body FE model was used to assess the responses of different regions of the brain to impact loads. Strain-rate, strain, and stress measures in the corpus callosum, midbrain, and brain stem were assessed. Results show that maximum strain-rates of 27 and 19 s^?1 are observed in the brain-stem and mid-brain, respectively. This could potentially lead to axonal injuries and neuronal cell death during crown impact conditions. The developed experimental-numerical framework can be used in the study of other helmet-related impact conditions.     

Environmental cues for cyclomorphosis in Daphnia retrocurva Forbes

SUMMARY.

• 1 The invertebrate predators. Chaohorus, Leptodora, Hydra, Utricularia, and cyclopoid copepods were ineffective as inducers of high helmets in laboratory reared Daphnia retrocurva. Lako water from different sources, when used as culture medium, was also ineffective.
• 2 High helmets were induced when clones were grown under warm and turbulent conditions. Presence or absence of illumination and varying photoperiod did not affect helmet growth in warm turbulent cultures. Different clones grown under warm turbulent conditions differed in their responsiveness to the treatment, but no relationship between helmet size in clones and helmet size in the field on the dates of clone isolation was demonstrated. Laboratory-induced phenotypes were rarely as extreme as those of field animals.

     

Simulation of the effects of different pilot helmets on neck loading during air combat

New generation pilot helmets with mounted devices enhance the capabilities of pilots substantially. However, the additional equipment increases the helmet weight and shifts its center of mass forward. Two helmets with different mass properties were modeled to simulate their effects on the pilot's neck. A musculoskeletal computer model was used, with the methods of inverse dynamics and static optimization, to compute the muscle activations and joint reaction forces for a given range of quasi-static postures at various accelerations experienced during air combat. Head postures which induce much higher loads on the cervical spine than encountered in a neutral position could be identified. The increased weight and the forward shift of the center of mass of a new generation helmet lead to higher muscle activations and higher joint reaction loads over a wide range of head and neck movements. The muscle activations required to balance the head and neck in extreme postures increased the compressive force at the T1-C7 level substantially, while in a neutral posture the muscle activations remained low. The lateral neck muscles can reach activations of 100% and cause compressive joint forces up to 1100N during extensive rotations and extensions at high 'vertical' accelerations (Gz). The calculated values have to be interpreted with care as the model has not been validated. Nevertheless, this systematic analysis could separate the effects of head posture, acceleration and helmet mass on neck loading. More reliable data about mass properties and muscle morphometry with a more detailed motion analysis would help to refine the existing model.