Individual Impact Magnitude vs. Cumulative Magnitude for Estimating Concussion Odds

Helmeted impact devices have allowed researchers to investigate the biomechanics of head impacts in vivo. While increased impact magnitude has been associated with greater concussion risk, a definitive concussive threshold has not been established. It is likely that concussion risk is not determined by a single impact itself, but a host of predisposing factors. These factors may include genetics, fatigue, and/or prior head impact exposure. The objective of the current paper is to investigate the association between cumulative head impact magnitude and concussion risk. It is hypothesized that increased cumulative magnitudes will be associated with greater concussion risk. This retrospective analysis included participants that were recruited from regional high-schools in Illinois and Michigan from 2007 to 2014 as part of an ongoing study on concussion biomechanics. Across seven seasons, 185 high school football athletes were instrumented with the Head Impact Telemetry system. Out of 185 athletes, 31 (17%) sustained a concussion, with two athletes sustaining two concussions over the study period, yielding 33 concussive events. The system recorded 78,204 impacts for all concussed players. Linear acceleration, rotational acceleration, and head impact telemetry severity profile (HITsp) magnitudes were summed within five timeframes: the day of injury, three days prior to injury, seven days prior to injury, 30 days prior to injury, and prior in-season exposure. Logistic regressions were modeled to explain concussive events based on the singular linear acceleration, rotational acceleration, and HITsp event along with the calculated summations over time. Linear acceleration, rotational acceleration, and HITsp all produced significant models estimating concussion (p < 0.05). The strongest estimators of a concussive impact were the linear acceleration (OR = 1.040, p < 0.05), rotational acceleration (OR = 1.001, p < 0.05), and HITsp (OR = 1.003, p < 0.05) for the singular impact rather than any of the cumulative magnitude calculations. Moreover, no cumulative count measure was significant for linear or rotational acceleration. Results from this investigation support the growing literature indicating cumulative magnitude is not related to concussion likelihood. Cumulative magnitude is a simplistic measure of the total exposure sustained by a player over a given period. However, this measure is limited as it assumes the brain is a static structure unable to undergo self-repair. Future research should consider how biological recovery between impacts may influence concussion risk.     

Head impact exposure in youth football

The head impact exposure for athletes involved in football at the college and high school levels has been well documented; however, the head impact exposure of the youth population involved with football has yet to be investigated, despite its dramatically larger population. The objective of this study was to investigate the head impact exposure in youth football. Impacts were monitored using a custom 12 accelerometer array equipped inside the helmets of seven players aged 7–8 years old during each game and practice for an entire season. A total of 748 impacts were collected from the 7 participating players during the season, with an average of 107 impacts per player. Linear accelerations ranged from 10 to 100 g, and the rotational accelerations ranged from 52 to 7694 rad/s². The majority of the high level impacts occurred during practices, with 29 of the 38 impacts above 40 g occurring in practices. Although less frequent, youth football can produce high head accelerations in the range of concussion causing impacts measured in adults. In order to minimize these most severe head impacts, youth football practices should be modified to eliminate high impact drills that do not replicate the game situations.     

Evaluation of Three Animal Models for Concussion and Serious Brain Injury

Three animal models were evaluated in this study involving head impacts of the rat, including the Marmarou drop-weight and two momentum-exchange techniques. In series 1, 36 Wistar rats were hit on the side of the free-moving head using Marmarou’s 450 g impact mass at 4.4, 5.4, and 6.3 m/s. Head acceleration was measured and injuries were observed. The 6.3-m/s side impact resulted in no deaths, no skull fractures, infrequent contusions, and some injuries consistent with diffuse axonal injury. In series 2, 57 Marmarou drop-weight tests were conducted to study head biomechanical responses. Marmarou’s technique involves a head impact followed by prolonged loading into a foam pad under the animal. Based on the literature, the 2 m (6.3 m/s) Marmarou drop causes death, skull fracture, brain and spinal cord contusions, and diffuse axonal injury. These injuries are more severe than that occurring with impact of similar mass and velocity to the free-moving head. Impacts to the free-moving head provide more realistic animal models to study concussion and severe brain injury.     

Change in Size and Impact Performance of Football Helmets from the 1970s to 2010

Linear impactor tests were conducted on football helmets from the 1970s–1980s to complement recently reported tests on 1990s and 2010s helmets. Helmets were placed on the Hybrid III head with an array of accelerometers to determine translational and rotational acceleration. Impacts were at four sites on the helmet shell at 3.6–11.2 m/s. The four generations of helmets show a continuous improvement in response from bare head impacts in terms of Head Injury Criterion (HIC), peak head acceleration and peak rotational acceleration. Helmets of 2010s weigh 1.95 ± 0.2 kg and are 2.7 times heavier than 1970s designs. They are also 4.3 cm longer, 7.6 cm higher, and 4.9 cm wider. The extra size and weight allow the use of energy absorbing padding that lowers forces in helmet impacts. For frontal impacts at 7.4 m/s, the four best performing 2010s helmets have HIC of 148 ± 23 compared to 179 ± 42 for the 1990s baseline, 231 ± 27 for the 1980s, 253 ± 22 for the 1970s helmets, and 354 ± 3 for the bare head. The additional size and padding of the best 2010s helmets provide superior attenuation of impact forces in normal play and in conditions associated with concussion than helmets of the 1970s–1990s.     

Concussions Experienced by Major League Baseball Catchers and Umpires: Field Data and Experimental Baseball Impacts

Some reports have shown that head injuries in baseball may comprise up to 18.5% of all competitive sports-related head injuries. The objective of this study was to evaluate the response of catcher and umpire masks to impacts at these different regions to discover the impact conditions that represent the greatest risk of injury. A series of 10 events in which a catcher or umpire in Major League Baseball, who experienced a foul ball to the mask that resulted in a concussion, were analyzed through video and data on pitch characteristics. It was found that the impacts were distributed across the face, and the median plate speed was approximately 38 m/s (84 mph). To determine the relative severity of each identified impact location, an instrumented Hybrid III head outfitted with a catcher or umpire mask was impacted with baseballs. Testing at 27 and 38 m/s (60 and 84 mph) suggested that impacts to the center-eyebrow and chin locations were the most severe. Peak linear and rotational accelerations were found to be lower than the suggested injury thresholds. While impacts to a mask result in head accelerations which are near or below levels commonly associated with the lower limits for head injury, the exact injury mechanism is unclear, as concussions are still experienced by the mask wearers.     

Head Impact Exposure in Youth Football: High School Ages 14 to 18 Years and Cumulative Impact Analysis

Sports-related concussion is the most common athletic head injury with football having the highest rate among high school athletes. Traditionally, research on the biomechanics of football-related head impact has been focused at the collegiate level. Less research has been performed at the high school level, despite the incidence of concussion among high school football players. The objective of this study is to twofold: to quantify the head impact exposure in high school football, and to develop a cumulative impact analysis method. Head impact exposure was measured by instrumenting the helmets of 40 high school football players with helmet mounted accelerometer arrays to measure linear and rotational acceleration. A total of 16,502 head impacts were collected over the course of the season. Biomechanical data were analyzed by team and by player. The median impact for each player ranged from 15.2 to 27.0 g with an average value of 21.7 (±2.4) g. The 95th percentile impact for each player ranged from 38.8 to 72.9 g with an average value of 56.4 (±10.5) g. Next, an impact exposure metric utilizing concussion injury risk curves was created to quantify cumulative exposure for each participating player over the course of the season. Impacts were weighted according to the associated risk due to linear acceleration and rotational acceleration alone, as well as the combined probability (CP) of injury associated with both. These risks were summed over the course of a season to generate risk weighted cumulative exposure. The impact frequency was found to be greater during games compared to practices with an average number of impacts per session of 15.5 and 9.4, respectively. However, the median cumulative risk weighted exposure based on combined probability was found to be greater for practices vs. games. These data will provide a metric that may be used to better understand the cumulative effects of repetitive head impacts, injury mechanisms, and head impact exposure of athletes in football.     

Measuring Head Kinematics in Football: Correlation Between the Head Impact Telemetry System and Hybrid III Headform

Over the last decade, advances in technology have enabled researchers to evaluate concussion biomechanics through measurement of head impacts sustained during play using two primary methods: (1) laboratory reconstruction of open-field head contact, and (2) instrumented helmets. The purpose of this study was to correlate measures of head kinematics recorded by the Head Impact Telemetry (HIT) System (Simbex, NH) with those obtained from a Hybrid III (HIII) anthropometric headform under conditions that mimicked impacts occurring in the NFL. Linear regression analysis was performed to correlate peak linear acceleration, peak rotational acceleration, Gadd Severity Index (GSI), and Head Injury Criterion (HIC₁₅) obtained from the instrumented helmet and HIII. The average absolute location error between instrumented helmet impact location and the direction of HIII head linear acceleration were also calculated. The HIT System overestimated Hybrid III peak linear acceleration by 0.9% and underestimated peak rotational acceleration by 6.1% for impact sites and velocities previously identified by the NFL as occurring during play. Acceleration measures for all impacts were correlated; however, linear was higher (r ² = 0.903) than rotational (r ² = 0.528) primarily due to lower HIT System rotational acceleration estimates at the frontal facemask test site. Severity measures GSI and HIC were also found to be correlated, albeit less than peak linear acceleration, with the overall difference between the two systems being less than 6.1% for either measure. Mean absolute impact location difference between systems was 31.2 ± 46.3° (approximately 0.038 ± 0.050 m), which was less than the diameter of the impactor surface in the test. In instances of severe helmet deflection (2.54–7.62 cm off the head), the instrumented helmet accurately measured impact location but overpredicted all severity metrics recorded by the HIII. Results from this study indicate that measurements from the two methods of study are correlated and provide a link that can be used to better interpret findings from future study using either technology.     

Head and neck loading in everyday and vigorous activities

The purpose of this study was to document head and neck loading in a group of ordinary people engaged in non-injurious everyday and more vigorous physical activities. Twenty (20) volunteers that were representative of the general population were subjected to seven test scenarios: a soccer ball impact to the forehead, a self-imposed hand strike to the forehead, vigorous head shaking, plopping down in a chair, jumping off a step, a seated drop onto the buttocks, and a vertical drop while seated supine in a chair. Some scenarios involved prescribed and well-controlled stimuli, while others allowed the volunteers to perform common activities at a self-selected level of intensity. Head accelerations up to 31 g and 2888 rad/s² and neck loads up to 268 N in posterior shear, 526 N in compression, and 36 Nm in extension were recorded. Most head and neck injury criteria predicted a low risk of injury in all activities. However, rotational head accelerations and Neck Injury Criterion (NIC) values were much higher than some proposed tolerance limits in a large number of tests, all of which were non-injurious. The data from this study help us to establish an envelope of head and neck loading that is commonly encountered and presents a minimal risk of injury.     

Validation of Concussion Risk Curves for Collegiate Football Players Derived from HITS Data

For several years, Virginia Tech and other schools have measured the frequency and severity of head impacts sustained by collegiate American football players in real time using the Head Impact Telemetry (HIT) System of helmet-mounted accelerometers. In this study, data from 37,128 head impacts collected at Virginia Tech during games from 2006 to 2010 were analyzed. Peak head acceleration exceeded 100 g in 516 impacts, and the Head Injury Criterion (HIC) exceeded 200 in 468 impacts. Four instrumented players in the dataset sustained a concussion. These data were used to develop risk curves for concussion as a function of peak head acceleration and HIC. The validity of this biomechanical approach was assessed using epidemiological data on concussion incidence from other sources. Two specific aspects of concussion incidence were addressed: the variation by player position, and the frequency of repeat concussions. The HIT System data indicated that linemen sustained the highest overall number of head impacts, while skill positions sustained a higher number of more severe head impacts (peak acceleration > 100 g or HIC > 200). When weighted using injury risk curves, the HIT System data predicted a higher incidence of concussion in skill positions compared to linemen at rates that were in strong agreement with the epidemiological literature (Pearson’s r = 0.72–0.87). The predicted rates of repeat concussions (21–39% over one season and 33–50% over five seasons) were somewhat higher than the ranges reported in the epidemiological literature. These analyses demonstrate that simple biomechanical parameters that can be measured by the HIT System possess a high level of power for predicting concussion.     

Head Impact Biomechanics in Youth Hockey: Comparisons Across Playing Position, Event Types, and Impact Locations

The age at which young hockey players should safely body check is unknown. We sought to determine if playing position (defensemen vs. forwards), event type (practice vs. game), or head impact location (top vs. back vs. front vs. sides) had an effect on head impact biomechanics in youth hockey. A total of 52 Bantam (13–14 years old) and Midget (15–16 years old) ice hockey players wore accelerometer-instrumented helmets for two seasons. Biomechanical data were captured for 12,253 head impacts during 151 games and 137 practices. Random intercepts general mixed linear models were employed to analyze differences in linear acceleration, rotational acceleration, and HITsp by player position, event type, and head impact location. Head impacts sustained during games resulted in greater rotational acceleration and HITsp than those sustained during practices. No event type or playing position differences in linear acceleration were observed. Impacts to the top of the head resulted in greater linear acceleration, but lower rotational acceleration and HITsp, than impacts to back, front, or side of the head. Side head impacts yielded greater rotational acceleration and HITsp compared to the other head impact locations. Since linear and rotational accelerations were observed in all impacts, future hockey helmet design standards should include rotational acceleration limits in addition to the current linear acceleration standards.     

Brain Injury Prediction: Assessing the Combined Probability of Concussion Using Linear and Rotational Head Acceleration

Recent research has suggested possible long term effects due to repetitive concussions, highlighting the importance of developing methods to accurately quantify concussion risk. This study introduces a new injury metric, the combined probability of concussion, which computes the overall risk of concussion based on the peak linear and rotational accelerations experienced by the head during impact. The combined probability of concussion is unique in that it determines the likelihood of sustaining a concussion for a given impact, regardless of whether the injury would be reported or not. The risk curve was derived from data collected from instrumented football players (63,011 impacts including 37 concussions), which was adjusted to account for the underreporting of concussion. The predictive capability of this new metric is compared to that of single biomechanical parameters. The capabilities of these parameters to accurately predict concussion incidence were evaluated using two separate datasets: the Head Impact Telemetry System (HITS) data and National Football League (NFL) data collected from impact reconstructions using dummies (58 impacts including 25 concussions). Receiver operating characteristic curves were generated, and all parameters were significantly better at predicting injury than random guessing. The combined probability of concussion had the greatest area under the curve for all datasets. In the HITS dataset, the combined probability of concussion and linear acceleration were significantly better predictors of concussion than rotational acceleration alone, but not different from each other. In the NFL dataset, there were no significant differences between parameters. The combined probability of concussion is a valuable method to assess concussion risk in a laboratory setting for evaluating product safety.     

Head Impact Exposure in Youth Football: Elementary School Ages 9–12 Years and the Effect of Practice Structure

Head impact exposure in youth football has not been well-documented, despite children under the age of 14 accounting for 70% of all football players in the United States. The objective of this study was to quantify the head impact exposure of youth football players, age 9–12, for all practices and games over the course of single season. A total of 50 players (age = 11.0 ± 1.1 years) on three teams were equipped with helmet mounted accelerometer arrays, which monitored each impact players sustained during practices and games. During the season, 11,978 impacts were recorded for this age group. Players averaged 240 ± 147 impacts for the season with linear and rotational 95th percentile magnitudes of 43 ± 7 g and 2034 ± 361 rad/s². Overall, practice and game sessions involved similar impact frequencies and magnitudes. One of the three teams however, had substantially fewer impacts per practice and lower 95th percentile magnitudes in practices due to a concerted effort to limit contact in practices. The same team also participated in fewer practices, further reducing the number of impacts each player experienced in practice. Head impact exposures in games showed no statistical difference. While the acceleration magnitudes among 9–12 year old players tended to be lower than those reported for older players, some recorded high magnitude impacts were similar to those seen at the high school and college level. Head impact exposure in youth football may be appreciably reduced by limiting contact in practices. Further research is required to assess whether such a reduction in head impact exposure will result in a reduction in concussion incidence.     

Effect of Mouthguards on Head Responses and Mandible Forces in Football Helmet Impacts

The potential for mouthguards to change the risk of concussion was studied in football helmet impacts. The Hybrid III head was modified with an articulating mandible, dentition, and compliant temporomandibular joints (TMJ). It was instrumented for triaxial head acceleration and triaxial force at the TMJs and upper dentition. Mandible force and displacement were validated against cadaver impacts to the chin. In phase 1, one of five mouthguards significantly lowered HIC in 6.7 m/s impacts (p = 0.025) from the no mouthguard condition but not in 9.5 m/s tests. In phase 2, eight mouthguards increased HIC from +1 to +17% in facemask impacts that loaded the chinstraps and mandible; one was statistically higher (p = 0.018). Peak head acceleration was +1 to +15% higher with six mouthguards and 2–3% lower with two others. The differences were not statistically significant. Five of eight mouthguards significantly reduced forces on the upper dentition by 40.8–63.9%. Mouthguards tested in this study with the Hybrid III articulating mandible lowered forces on the dentition and TMJ, but generally did not influence HIC or concussion risks.     

The WRAIR Projectile Concussive Impact Model of Mild Traumatic Brain Injury: Re-design,Testing and Preclinical Validation

The WRAIR projectile concussive impact (PCI) model was developed for preclinical study of concussion. It represents a truly non-invasive closed-head injury caused by a blunt impact. The original design, however, has several drawbacks that limit the manipulation of injury parameters. The present study describes engineering advancements made to the PCI injury model including helmet material testing, projectile impact energy/head kinematics and impact location. Material testing indicated that among the tested materials, ‘fiber-glass/carbon’ had the lowest elastic modulus and yield stress for providing an relative high percentage of load transfer from the projectile impact, resulting in significant hippocampal astrocyte activation. Impact energy testing of small projectiles, ranging in shape and size, showed the steel sphere produced the highest impact energy and the most consistent impact characteristics. Additional tests confirmed the steel sphere produced linear and rotational motions on the rat’s head while remaining within a range that meets the criteria for mTBI. Finally, impact location testing results showed that PCI targeted at the temporoparietal surface of the rat head produced the most prominent gait abnormalities. Using the parameters defined above, pilot studies were conducted to provide initial validation of the PCI model demonstrating quantifiable and significant increases in righting reflex recovery time, axonal damage and astrocyte activation following single and multiple concussions.     

Impact Performance of Modern Football Helmets

Linear impact tests were conducted on 17 modern football helmets. The helmets were placed on the Hybrid III head with the neck attached to a sliding table. The head was instrumented with an array of 3-2-2-2 accelerometers to determine translational acceleration, rotational acceleration, and HIC. Twenty-three (23) different impacts were conducted on four identical helmets of each model at eight sites on the shell and facemask, four speeds (5.5, 7.4, 9.3, and 11.2 m/s) and two temperatures (22.2 and 37.8 °C). There were 1,850 tests in total; 276 established the 1990s helmet performance (baseline) and 1,564 were on the 17 different helmet models. Differences from the 1990s baseline were evaluated using the Student t test (p < 0.05 as significant). Four of the helmets had significantly lower HICs and head accelerations than the 1990s baseline with average reductions of 14.6–21.9% in HIC, 7.3–14.0% in translational acceleration, and 8.4–15.9% in rotational acceleration. Four other helmets showed some improvements. Eight were not statistically different from the 1990s baseline and one had significantly poorer performance. Of the 17 helmet models, four provided a significant reduction in head responses compared to 1990s helmets.     

Estimated Brain Tissue Response Following Impacts Associated With and Without Diagnosed Concussion

Kinematic measurements of head impacts are sensitive to sports concussion, but not highly specific. One potential reason is these measures reflect input conditions only and may have varying degrees of correlation to regional brain tissue deformation. In this study, previously reported head impact data recorded in the field from high school and collegiate football players were analyzed using two finite element head models (FEHM). Forty-five impacts associated with immediately diagnosed concussion were simulated along with 532 control impacts without identified concussion obtained from the same players. For each simulation, intracranial response measures (max principal strain, strain rate, von Mises stress, and pressure) were obtained for the whole brain and within four regions of interest (ROI; cerebrum, cerebellum, brain stem, corpus callosum). All response measures were sensitive to diagnosed concussion; however, large inter-athlete variability was observed and sensitivity strength depended on measure, ROI, and FEHM. Interestingly, peak linear acceleration was more sensitive to diagnosed concussion than all intracranial response measures except pressure. These findings suggest FEHM may provide unique and potentially important information on brain injury mechanisms, but estimations of concussion risk based on individual intracranial response measures evaluated in this study did not improve upon those derived from input kinematics alone.     

Hybrid III ATD in Inverted Impacts: Influence of Impact Angle on Neck Injury Risk Assessment

The purpose of this paper is to present a protocol of inverted drop-tests using a 50th percentile Hybrid III Anthropomorphic Test Device (ATD) and investigate the influence of angle and velocity at impact on neck injury risk assessment. The tests were based on existing cadaveric experimental protocols for inverted seated positions. In this study selected ATD impact orientations were also assessed in both the sagittal and coronal planes. Twenty-six tests were performed at impact velocities from 1.4 to 3.1 m s⁻¹. The drop tests confirmed previously described behavior of the ATD in axial loading of its head/neck/thorax complex. They also showed a significant influence of the initial impact angle on neck injury criteria currently used by researchers in rollover crashworthiness tests. At 1.4 m s⁻¹, the peak upper neck axial force of 4350 N was reduced by an average 1760 ± 80 N for configurations with 30 degrees initial impact angle in any plane, compared to a reference inverted vertical configuration. The N _ij was also significantly influenced. For a given impact velocity, an out-of-both-planes initial configuration resulted in the highest combined outputs. Based on these results, similar dynamic conditions (intrusion velocity, impact duration) may result in significantly different loadings of the Hybrid III neck.     

Head-Impact Mechanisms in Men's and Women's Collegiate Ice Hockey

Context:

Concussion injury rates in men''s and women''s ice hockey are reported to be among the highest of all collegiate sports. Quantification of the frequency of head impacts and the magnitude of head acceleration as a function of the different impact mechanisms (eg, head contact with the ice) that occur in ice hockey could provide a better understanding of this high injury rate.

Objective:

To quantify and compare the per-game frequency and magnitude of head impacts associated with various impact mechanisms in men''s and women''s collegiate ice hockey players.

Design:

Cohort study.

Setting:

Collegiate ice hockey rink.

Patients or Other Participants:

Twenty-three men and 31 women from 2 National Collegiate Athletic Association Division I ice hockey teams.

Main Outcome Measure(s):

We analyzed magnitude and frequency (per game) of head impacts per player among impact mechanisms and between sexes using generalized mixed linear models and generalized estimating equations to account for repeated measures within players.

Intervention(s):

Participants wore helmets instrumented with accelerometers to allow us to collect biomechanical measures of head impacts sustained during play. Video footage from 53 games was synchronized with the biomechanical data. Head impacts were classified into 8 categories: contact with another player; the ice, boards or glass, stick, puck, or goal; indirect contact; and contact from celebrating.

Results:

For men and women, contact with another player was the most frequent impact mechanism, and contact with the ice generated the greatest-magnitude head accelerations. The men had higher per-game frequencies of head impacts from contact with another player and contact with the boards than did the women (P < .001), and these impacts were greater in peak rotational acceleration (P = .027).

Conclusions:

Identifying the impact mechanisms in collegiate ice hockey that result in frequent and high-magnitude head impacts will provide us with data that may improve our understanding of the high rate of concussion in the sport and inform injury-prevention strategies.Key Words: impact biomechanics, sport, concussion, sex

Key Points

• The most frequent head-impact mechanism in both men''s and women''s collegiate ice hockey was contact with another player. Contact with the ice was the mechanism that resulted in head impacts with the greatest magnitude.
• Male collegiate ice hockey players experienced head impacts from contact with another player and contact with the boards more frequently than did female players, and these impacts were generally of greater magnitude.

Ice hockey is a high-intensity, high-speed collision sport in which most injuries are caused by blunt trauma or direct contact with another player or object as opposed to overuse injuries.¹ High rates of injury have been reported in both men''s and women''s collegiate ice hockey (5.95/1000 and 5.12/1000 athlete-exposures [AEs], respectively), and the most common injury in both populations is concussion.² The rate of concussion has been reported to be higher in women''s ice hockey (0.82/1000 AEs) than in men''s (0.72/1000 AEs), but the reasons for this are not well understood.² Concussions are usually attributed to a direct impact to the head but can also be caused by an impact to the body that results in an acceleration of the head.³ The high rate of injury, including concussions, in ice hockey can be attributed to the unique factors of the game: the playing area is made of solid ice and enveloped by rigid boards, players manipulate pucks that, when shot, can exceed speeds of 80 mph (117 kph), and players travel at speeds of up to 30 mph (44 kph) and purposefully collide with opponents.^4,5 These factors allow for a number of different head-impact mechanisms, or circumstances in which a head impact occurs (head contact with ice, boards, etc), in ice hockey.Currently, data quantifying the biomechanics of head impacts as a function of the different impact mechanisms that occur in ice hockey are lacking. Previous authors^6,7 have quantified the frequency and magnitude of head impacts in cohorts of male and female hockey players at different levels of play using the Head Impact Telemetry (HIT) System (Simbex, Lebanon, NH). The HIT System measures and records biomechanical data from head impacts, including the linear and rotational acceleration of the head, impact duration, and impact location on the helmet.^5–19 These studies have provided valuable information on individual players'' exposure to head impacts but did not identify or examine the relationship with mechanisms of impact. Other researchers^2,4,20–22 have reported injury epidemiology, including diagnosed concussions, by specific injury mechanisms in collegiate ice hockey. Agel et al^20,21 used the National Collegiate Athletic Association (NCAA) Injury Surveillance System to report concussion mechanisms in collegiate men and women. Diagnosed concussions were classified into 1 of 7 mechanisms: contact with another player, contact with the ice surface, contact with the boards or glass, contact with the goal, contact with the stick, contact with the puck, or no apparent contact. Another author²³ classified injury mechanisms in National Hockey League players by reviewing video footage from games in which diagnosed concussions occurred. The most common mechanism that resulted in diagnosed concussions for both studies was player-to-player contact.^20,21,23 Although these assessments provided important information on injury and concussion mechanisms in ice hockey, the collection and analysis of the impact biomechanics that resulted from these mechanisms were beyond the scope of the study designs. Synchronizing video with the biomechanics of head impacts would provide a quantitative approach to evaluating head impact mechanisms and biomechanics.The aim of our study was to quantify and compare the frequency and magnitude of head impacts associated with various impact mechanisms in men''s and women''s collegiate ice hockey players. We accomplished this by synchronizing video footage from games with biomechanical data from the HIT System. We hypothesized that the frequency and magnitude of head impacts would differ among the various head-impact mechanisms and that sex would be a significant factor in both frequency and magnitude.     

Nano-Composite Foam Sensor System in Football Helmets

American football has both the highest rate of concussion incidences as well as the highest number of concussions of all contact sports due to both the number of athletes and nature of the sport. Recent research has linked concussions with long term health complications such as chronic traumatic encephalopathy and early onset Alzheimer’s. Understanding the mechanical characteristics of concussive impacts is critical to help protect athletes from these debilitating diseases and is now possible using helmet-based sensor systems. To date, real time on-field measurement of head impacts has been almost exclusively measured by devices that rely on accelerometers or gyroscopes attached to the player’s helmet, or embedded in a mouth guard. These systems monitor motion of the head or helmet, but do not directly measure impact energy. This paper evaluates the accuracy of a novel, multifunctional foam-based sensor that replaces a portion of the helmet foam to measure impact. All modified helmets were tested using a National Operating Committee Standards for Athletic Equipment-style drop tower with a total of 24 drop tests (4 locations with 6 impact energies). The impacts were evaluated using a headform, instrumented with a tri-axial accelerometer, mounted to a Hybrid III neck assembly. The resultant accelerations were evaluated for both the peak acceleration and the severity indices. These data were then compared to the voltage response from multiple Nano Composite Foam sensors located throughout the helmet. The foam sensor system proved to be accurate in measuring both the HIC and Gadd severity index, as well as peak acceleration while also providing additional details that were previously difficult to obtain, such as impact energy.     

High School and Collegiate Football Athlete Concussions: A Biomechanical Review

Researchers are striving to understand the biomechanics of concussive injury that occur in the context of sport by using a number of methodologies. Animal models, video reconstruction, and helmet-based accelerometers have all been used, but have their limitations. The Head Impact Telemetry (HIT) System permits the real-time in vivo tracking of all impacts that occur on the football field and has been used in both the high school and collegiate setting. This review provides a theoretical discussion of concussion mechanics and examines the current literature on the effects of the number of impacts, impact magnitude, impact distribution, and concussion threshold in high school and collegiate football athletes recorded by the HIT System.