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).     

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.     

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.     

Validation of a wireless head acceleration measurement system for use in soccer play

Soccer heading has been studied previously with conflicting results. One major issue is the lack of knowledge regarding what actually occurs biomechanically during soccer heading impacts. The purpose of the current study is to validate a wireless head acceleration measurement system, head impact telemetry system (HITS) that can be used to collect head accelerations during soccer play. The HIT system was fitted to a Hybrid III (HIII) head form that was instrumented with a 3-2-2-2 accelerometer setup. Fifteen impact conditions were tested to simulate impacts commonly experienced during soccer play. Linear and angular acceleration were calculated for both systems and compared. Root mean square (RMS) error and cross correlations were also calculated and compared for both systems. Cross correlation values were very strong with r = .95 ± 0.02 for ball to head forehead impacts and r = .96 ± 0.02 for head to head forehead impacts. The systems showed a strong relationship when comparing RMS error, linear head acceleration, angular head acceleration, and the cross correlation values.     

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.     

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.     

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.     

Persistent,Long-term Cerebral White Matter Changes after Sports-Related Repetitive Head Impacts

Introduction

Repetitive head impacts (RHI) sustained in contact sports are thought to be necessary for the long-term development of chronic traumatic encephalopathy (CTE). Our objectives were to: 1) characterize the magnitude and persistence of RHI-induced white matter (WM) changes; 2) determine their relationship to kinematic measures of RHI; and 3) explore their clinical relevance.

Methods

Prospective, observational study of 10 Division III college football players and 5 non-athlete controls during the 2011-12 season. All subjects underwent diffusion tensor imaging (DTI), physiologic, cognitive, and balance testing at pre-season (Time 1), post-season (Time 2), and after 6-months of no-contact rest (Time 3). Head impact measures were recorded using helmet-mounted accelerometers. The percentage of whole-brain WM voxels with significant changes in fractional anisotropy (FA) and mean diffusivity (MD) from Time 1 to 2, and Time 1 to 3 was determined for each subject and correlated to head impacts and clinical measures.

Results

Total head impacts for the season ranged from 431–1,850. No athlete suffered a clinically evident concussion. Compared to controls, athletes experienced greater changes in FA and MD from Time 1 to 2 as well as Time 1 to 3; most differences at Time 2 persisted to Time 3. Among athletes, the percentage of voxels with decreased FA from Time 1 to 2 was positively correlated with several helmet impact measures. The persistence of WM changes from Time 1 to 3 was also associated with changes in serum ApoA1 and S100B autoantibodies. WM changes were not consistently associated with cognition or balance.

Conclusions

A single football season of RHIs without clinically-evident concussion resulted in WM changes that correlated with multiple helmet impact measures and persisted following 6 months of no-contact rest. This lack of WM recovery could potentially contribute to cumulative WM changes with subsequent RHI exposures.     

Head impact exposure in male and female collegiate ice hockey players

The purpose of this study was to quantify head impact exposure (frequency, location and magnitude of head impacts) for individual male and female collegiate ice hockey players and to investigate differences in exposure by sex, player position, session type, and team. Ninety-nine (41 male, 58 female) players were enrolled and 37,411 impacts were recorded over three seasons. Frequency of impacts varied significantly by sex (males: 287 per season, females: 170, p<0.001) and helmet impact location (p<0.001), but not by player position (p=0.088). Head impact frequency also varied by session type; both male and female players sustained more impacts in games than in practices (p<0.001), however the magnitude of impacts did not differ between session types. There was no difference in 95th percentile peak linear acceleration between sexes (males: 41.6 g, females: 40.8 g), but 95th percentile peak rotational acceleration and HITsp (a composite severity measure) were greater for males than females (4424, 3409 rad/s², and 25.6, 22.3, respectively). Impacts to the back of the helmet resulted in the greatest 95th percentile peak linear accelerations for males (45.2 g) and females (50.4 g), while impacts to the side and back of the head were associated with the greatest 95th percentile peak rotational accelerations (males: 4719, 4256 rad/sec², females: 3567, 3784 rad/sec² respectively). It has been proposed that reducing an individual's head impact exposure is a practical approach for reducing the risk of brain injuries. Strategies to decrease an individual athlete's exposure need to be sport and gender specific, with considerations for team and session type.     

Verification of biomechanical methods employed in a comprehensive study of mild traumatic brain injury and the effectiveness of American football helmets

Concussion, or mild traumatic brain injury, occurs in many activities, mostly as a result of the head being accelerated. A comprehensive study has been conducted to understand better the mechanics of the impacts associated with concussion in American football. This study involves a sequence of techniques to analyse and reconstruct many different head impact scenarios. It is important to understand the validity and accuracy of these techniques in order to be able to use the results of the study to improve helmets and helmet standards. Two major categories of potential errors have been investigated. The first category concerns error sources specific to the use of crash test dummy instrumentation (accelerometers) and associated data processing techniques. These are relied upon to establish both linear and angular head acceleration responses. The second category concerns the use of broadcast video data and crash test dummy head-neck-torso systems. These are used to replicate the complex head impact scenarios of whole body collisions that occur on the football field between two living human beings. All acceleration measurement and processing techniques were based on well-established practices and standards. These proved to be reliable and reproducible. Potential errors in the linear accelerations due to electrical or mechanical noise did not exceed 2% for the three different noise sources investigated. Potential errors in the angular accelerations due to noise could be as high as 6.7%, due to error accumulation of multiple linear acceleration measurements. The potential error in the relative impact velocity between colliding heads could be as high as 11%, and was found to be the largest error source in the sequence of techniques to reconstruct the game impacts. Full-scale experiments with complete crash test dummies in staged head impacts showed maximum errors of 17% for resultant linear accelerations and 25% for resultant angular accelerations.     

BIOMECHANICS OF HEAD INJURY IN OLYMPIC TAEKWONDO AND BOXING

Objective

The purpose was to examine differences between taekwondo kicks and boxing punches in resultant linear head acceleration (RLA), head injury criterion (HIC15), peak head velocity, and peak foot and fist velocities. Data from two existing publications on boxing punches and taekwondo kicks were compared.

Methods

For taekwondo head impacts a Hybrid II Crash Dummy (Hybrid II) head was instrumented with a tri-axial accelerometer mounted inside the Hybrid II head. The Hybrid II was fixed to a height-adjustable frame and fitted with a protective taekwondo helmet. For boxing testing, a Hybrid III Crash Dummy head was instrumented with an array of tri-axial accelerometers mounted at the head centre of gravity.

Results

Differences in RLA between the roundhouse kick (130.11±51.67 g) and hook punch (71.23±32.19 g, d = 1.39) and in HIC15 (clench axe kick: 162.63±104.10; uppercut: 24.10±12.54, d = 2.29) were observed.

Conclusions

Taekwondo kicks demonstrated significantly larger magnitudes than boxing punches for both RLA and HIC.     

Significance of Ubiquitin Carboxy-Terminal Hydrolase L1 Elevations in Athletes after Sub-Concussive Head Hits

The impact of sub-concussive head hits (sub-CHIs) has been recently investigated in American football players, a population at risk for varying degrees of post-traumatic sequelae. Results show how sub-CHIs in athletes translate in serum as the appearance of reporters of blood-brain barrier disruption (BBBD), how the number and severity of sub-CHIs correlate with elevations of putative markers of brain injury is unknown. Serum brain injury markers such as UCH-L1 depend on BBBD. We investigated the effects of sub-CHIs in collegiate football players on markers of BBBD, markers of cerebrospinal fluid leakage (serum beta 2-transferrin) and markers of brain damage. Emergency room patients admitted for a clinically-diagnosed mild traumatic brain injury (mTBI) were used as positive controls. Healthy volunteers were used as negative controls. Specifically this study was designed to determine the use of UCH-L1 as an aid in the diagnosis of sub-concussive head injury in athletes. The extent and intensity of head impacts and serum values of S100B, UCH-L1, and beta-2 transferrin were measured pre- and post-game from 15 college football players who did not experience a concussion after a game. S100B was elevated in players experiencing the most sub-CHIs; UCH-L1 levels were also elevated but did not correlate with S100B or sub-CHIs. Beta-2 transferrin levels remained unchanged. No correlation between UCH-L1 levels and mTBI were measured in patients. Low levels of S100B were able to rule out mTBI and high S100B levels correlated with TBI severity. UCH-L1 did not display any interpretable change in football players or in individuals with mild TBI. The significance of UCH-L1 changes in sub-concussions or mTBI needs to be further elucidated.     

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.     

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.     

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.     

Anthropometric dimensions do not enhance one repetition maximum prediction from the NFL-225 test in college football players

The purpose of this study was to evaluate the contribution of anthropometric dimensions to improving the accuracy of repetitions-to-fatigue (RTF) using an absolute load of 225 lbs to predict 1 repetition maximum (1RM) bench press performance in college football players. Sixty-one players from an NCAA Division II team were evaluated for 1RM bench press performance, RTF using an absolute load of 225 lbs, and measured (5 skinfolds, 2 skeletal length, and 2 muscle circumferences). Anthropometric dimensions (percent fat, lean body mass, and arm cross-sectional areas) were derived at the conclusion of 8 weeks of heavy resistance training during the off-season. None of the anthropometric dimensions made a significant additional contribution to RTF (r = 0.96, SEE = 12.3 lbs) for predicting 1RM. Of the currently available NFL-225 prediction equations found in the literature nonsignificantly underestimated 1RM from RTF by an average of 1.1 lbs (+/-12.7 lbs), whereas 5 other RTF equations significantly overpredicted by 3.5-9.0 lbs (+/-12.2-14.1 lbs). Anthropometric dimensions neither reduced the error associated with prediction of 1RM bench press using the NFL-225 test in college football players nor do they explain why some players are significantly over- or underpredicted when using muscle endurance repetitions.     

A comparison of the magnitude and duration of linear and rotational head accelerations generated during hand-, elbow- and shoulder-to-head checks delivered by hockey players

Ice hockey has the highest rates for concussion among team sports in Canada. In elite play, the most common mechanism is impact to the head by an opposing player’s upper limb, with shoulder-to-head impacts accounting for twice as many concussions as elbow- and hand-to-head impacts combined. Improved understanding of the biomechanics of head impacts in hockey may inform approaches to prevention. In this study, we measured the magnitude and duration of linear and rotational head accelerations when hockey players (n = 11; aged 21–25) delivered checks “as hard as comfortable” to the head of an instrumented dummy with their shoulder, elbow and hand. There were differences in both peak magnitude and duration of head accelerations across upper limb impact sites, based on repeated-measures ANOVA (p < 0.005). Peak linear head accelerations averaged 1.9-fold greater for hand and 1.3-fold greater for elbow than shoulder (mean values = 20.35, 14.23 and 10.55 g, respectively). Furthermore, peak rotational head accelerations averaged 2.1-fold greater for hand and 1.8-fold greater for elbow than shoulder (1097.9, 944.1 and 523.1 rad/s², respectively). However, times to peak linear head acceleration (a measure of the duration of the acceleration impulse) were 2.1-fold longer for shoulder than elbow, and 2.5-fold longer for shoulder than hand (12.26, 5.94 and 4.98 ms, respectively), and there were similar trends in the durations of rotational head acceleration. Our results show that, in body checks to the head delivered by varsity-level hockey players, shoulder-to-head impacts generated longer durations but lower magnitude of peak head acceleration than elbow- and hand-to-head impacts.     

The effect of football helmet facemasks on impact behavior during linear drop tests

Football helmet certification tests are performed without a facemask attached to the helmet; however, the facemask is expected to contribute substantially to the structure and dynamics of the helmet through the effects of added mass and added stiffness. Facemasks may increase the peak acceleration and severity index; therefore, as-used helmets may not mitigate head impacts as effectively as certification tests indicate. Furthermore, the effect is expected to depend on the helmet design as well as the orientation and speed of the impact. This study examined the influence of the facemask on impact behavior in a NOCSAE-style linear drop test and the interactions with location, velocity, and helmet model. Increases in peak acceleration and severity index of up to 36% were observed when helmets were tested with the facemask.     

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

The scalp plays a crucial role in head impact biomechanics, being the first tissue involved in the impact and providing a sliding interface between the impactor and/or helmet and the skull. It is important to understand both the scalp-skull and the scalp-helmet sliding in order to determine the head response due to an impact. However, experimental data on the sliding properties of the scalp is lacking. The aim of this work was to identify the sliding properties of the scalp using cadaver heads, in terms of scalp-skull and scalp-liner (internal liner of the helmet) friction and to compare these values with that of widely used artificial headforms (HIII and magnesium EN960). The effect of the hair, the direction of sliding, the speed of the test and the normal load were considered. The experiments revealed that the sliding behaviour of the scalp under impact loading is characterised by three main phases: (1) the low friction sliding of the scalp over the skull (scalp-skull friction), (2) the tensioning effect of the scalp and (3) the sliding of the liner fabric over the scalp (scalp-liner friction). Results showed that the scalp-skull coefficient of friction (COF) is very low (0.06 ± 0.048), whereas the scalp-liner COF is 0.29 ± 0.07. The scalp-liner COF is statistically different from the value of the HIII-liner (0.75 ± 0.06) and the magnesium EN960-liner (0.16 ± 0.026). These data will lead to the improvement of current headforms for head impact standard tests, ultimately leading to more realistic head impact simulations and the optimization of helmet designs.     

A computational study of influence of helmet padding materials on the human brain under ballistic impacts

The results of a computational study of a helmeted human head are presented in this paper. The focus of the work is to study the effects of helmet pad materials on the level of acceleration, inflicted pressure and shear stress in a human brain model subjected to a ballistic impact. Four different closed cell foam materials, made of expanded polystyrene and expanded polypropylene, are examined for the padding material. It is assumed that bullets cannot penetrate the helmet shell. Finite element modelling of the helmet, padding system, head and head components is used for this dynamic nonlinear analysis. Appropriate contacts and conditions are applied between the different components of the head, as well as between the head and the pads, and the pads and the helmet. Based on the results of simulations in this work, it is concluded that the stiffness of the foam has a prominent role in reducing the level of the transferred load to the brain. A pad that is less stiff is more efficient in absorbing the impact energy and reducing the sudden acceleration of the head and consequently lowers the brain injury level. Using the pad with the least stiffness, the influence of the angle of impacts as well as the locations of the ballistic strike is studied.