Quantifying Youth Football Helmet Performance: Assessing Linear and Rotational Head Acceleration

Equestrian STAR: Development of an Experimental Methodology for Assessing the Biomechanical Performance of Equestrian Helmets

PURPOSE

The current equestrian helmet standards set minimal requirements for passing helmets, highlighting the need for a rating system that differentiates helmets based on their impact performance. This study's objectives were to compare equestrian helmet impact response kinematics between linear-driven and oblique impact conditions and then to evaluate the effect of incorporating oblique drop tests into a previously established equestrian helmet rating system, Equestrian STAR.

METHODS

Oblique drop tests were conducted with 45 equestrian helmet models at two impact locations, front boss and rear boss, at an impact velocity of 6.56 m/s. The resulting peak linear and rotational head accelerations were compared to those measured during linear-driven pendulum impacts on the same helmet models. A total of 720 impact tests were performed, making this the largest published study on equestrian helmets to date. Equestrian STAR was modified to include both pendulum and oblique impacts by computing and summing weighted concussion risks for each test condition.

RESULTS

Oblique impacts had peak linear accelerations ranging from 105.8 to 204.5 g and peak rotational accelerations ranging from 3304 to 13854 rad/s2. Between the linear-driven and oblique impacts, peak linear acceleration was weakly correlated (R2 = 0.34, p < 0.001), while peak rotational acceleration was not correlated (R2 = 0.04, p = 0.21). Equestrian STAR scores calculated using both pendulum and oblique impacts suggested that the worst-performing helmet on both systems had nearly four times the concussion risk as the best-performing.

CONCLUSION

Pendulum and oblique impacts have different methods of generating head rotation, which can highlight different modes of helmet performance. The updated Equestrian STAR helmet rating system differentiates between high-performing and low-performing helmets, enabling equestrians to purchase helmets best at reducing concussion risk and providing companies with a process to compare their helmet designs.

Youth football helmet fit assessment and association of prior fitting, issuance and initial season

The purpose of the study was to describe helmet fitting characteristics and influence of prior helmet fitting, issuance and initial season in a sample of youth football athletes. Helmet fit was assessed for 69 athletes aged 8-14 years using a standardized, 9-point inspection. Associated variables for improper fit consisted of previous fitting of helmet for the season, helmet issuance [team/school issued or purchased individually] and year of helmet initial season within 3 years of current season. A series of chi-square tests for association were conducted between the overall helmet fit and the associated variables. In total, 53.6% of youth football athletes had an improperly fit helmet, with 20.3% having ≥ three inspection items not meet fitting criteria. There were no associations between proper fit and previous fitting (p = 0.52), helmet issuance (p = 0.96) and year of initial season (p = 0.23). In conclusion, there were no associations between proper helmet fit and prior fitting, helmet issuance or year of initial season.

Quantifying Effects of Design Features on Youth Bicycle Helmet Performance During Oblique Impacts

PURPOSE

Cycling is a leading cause of youth sports-related head injury in the U.S. Although youth bicycle helmets sold in the U.S. comply with safety standards limiting head linear acceleration, there needs to be more information on relative differences in protection between helmets that pass. Additionally, studies have yet to look at quantifying youth bicycle helmet performance with respect to their design.

METHODS

Twenty-one youth bicycle helmet models were subjected to oblique impacts at three locations and two impact speeds where peak linear acceleration (PLA) and peak rotational acceleration (PRA) were quantified. Design features were characterized, including expanded polystyrene (EPS) thickness and presence of shell protrusions. A linear mixed model was used to quantify the effects of design features on PLA and PRA.

RESULTS

The youth bicycle helmet models evaluated produced wide ranges in kinematics across all configurations. PLA averaged 95.9 ± 26.1 g at 3.1 m/s and 170.1 ± 43.5 g at 5.2 m/s, while PRA averaged 3150 ± 1275 rad/s2 at 3.1 m/s and 4990 ± 1977 rad/s2 at 5.2 m/s. Impact location, impact speed, and EPS thickness had strong effects on PLA and PRA, whereas shell protrusions only had strong effects on PLA.

CONCLUSION

Youth bicycle helmets with thicker EPS, thinner shells, and shell protrusions at impact locations improved the linear and rotational kinematic measures. Limitations include the small sample size and the impacts analyzed not representing all possible real-world scenarios.

Concussion leads to opposing sensorimotor effects of habituation deficit and fatigue in zebrafish larvae

Concussion, or mild traumatic brain injury, is caused by sudden mechanical forces impacting the brain either directly or through inertial loading. This can lead to physical, behavioural and cognitive impairments. Despite concussion being a significant health issue, our understanding of the relationship between initial impact force and the subsequent neurological consequences is not well understood. Previously, we established a model of concussion in zebrafish larvae. Here, we further investigate concussions of varying severities in zebrafish larvae using linear deceleration. Using an acoustic assay to monitor the larval sensorimotor behaviour, we found that different parameters of the resulting escape behaviour are modulated by the impact force of the preceding concussive insult. To investigate the relative contributions of habituation performance and fatigue on the escape response behaviour, we constructed a neurocomputational model. Our findings suggest that a concussive impact initially affects habituation performance at first and, as the impact force increases, fatigue is induced. Fatigue then alters the escape response behaviour in an opposing manner.

Association of Sport Helmet Status on Concussion Presentation and Recovery in Male Collegiate Student-Athletes

Sporting helmets contain force attenuating materials which reduce traumatic head injury risk and may influence sport-related concussion (SRC) sequelae. The purpose of this study was to examine the association of sport helmet status with SRC-clinical presentation and recovery trajectories in men's collegiate athletes. Sport helmet status was based on the nature of sports being either helmeted/non-helmeted. 1070 SRCs in helmeted (HELM) sports (Men's-Football, Ice Hockey, and Lacrosse), and 399 SRCs in non-helmeted (NOHELM) sports (Men's-Basketball, Cheerleading, Cross Country/Track & Field, Diving, Gymnastics, Soccer, Swimming, Tennis, and Volleyball) were analyzed. Multivariable negative binomial regression models analyzed associations between sport helmet status and post-injury cognition, balance, and symptom severity, adjusting for covariate effects (SRC history, loss of consciousness, anterograde/retrograde amnesia, event type). Kaplan-Meier curves evaluated median days to: initiation of return to play (iRTP) protocol, and unrestricted RTP (URTP) by sport helmet status. Log-rank tests were used to evaluate differential iRTP/URTP between groups. Two independent multivariable Weibull accelerated failure time models were used to examine differential iRTP and URTP between groups, after adjusting for aforementioned covariates and symptom severity score. Overall, the median days to iRTP and URTP was 6.3 and 12.0, respectively, and was comparable across NOHELM- and HELM-SRCs. Post-injury symptom severity was lower (Score Ratio 0.90, 95%CI 0.82, 0.98), and cognitive test performance was higher (Score Ratio 1.03, 95%CI 1.02, 1.05) in NOHELM-compared to HELM-SRCs. Estimated time spent recovering to iRTP/URTP was comparable between sport helmet status groups. Findings suggest that the grouping of sports into helmeted and non-helmeted show slight differences in clinical presentation but not recovery.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Comparing Impact and Concussion Risk in Leatherhead and Modern Football and Hockey Helmets

BACKGROUND

Improvements in the modern helmet have demonstrated beneficial effects in reducing concussion risk in football players. However, previous studies yield conflicting results regarding the protective quality of leatherhead football helmets. There is limited research comparing the modern football helmet and the modern hockey helmet, with one previous study demonstrating the football helmet as providing a lower risk of concussion.

OBJECTIVE

To compare the head acceleration produced in a leatherhead football helmet vs a modern football helmet vs a modified modern football helmet with softer padding vs a modern hockey helmet in helmet-to-helmet strikes.

METHODS

Accelerometers were placed on the frontal, apex, and parietal regions of a Century Body Opponent Bag manikin. Each type of helmet was placed on the manikin and struck by a swinging modern football helmet. The G-force acceleration was determined in three-dimensional axes of 100 total helmet-to-helmet impacts.

RESULTS

The leatherhead football helmet was the least protective in reducing G-forces. The modified modern football helmet did not provide a significant difference compared with the modern football helmet. Significantly greater G-forces were produced in a collision between 2 modern football helmets in comparison with 2 modern hockey helmets.

CONCLUSION

The leatherhead football helmet was the least protective, and the hockey helmet was the most protective, with the football helmet being intermediate. This study provides additional insight into the inconclusive evidence regarding the safety of leatherhead football helmets and into the design of football and hockey helmets in the future.

Youth Tackle Football Head-Impact Estimation by Players and Parents: Is the Perception the Reality?

CONTEXT

With growing concerns surrounding exposure to head impacts in youth tackle football, players and parents must understand the exposure level when assenting and consenting to participate.

OBJECTIVE

To determine whether youth football players and parents could estimate on-field head-impact frequency, severity, and location.

DESIGN

Prospective cohort study.

SETTING

Football field.

PATIENTS OR OTHER PARTICIPANTS

We administered a 10-question head-impact estimation tool to parents (n = 23; mean age = 36.5 years [95% CI = 31.7, 37.3 years]) and players (n = 16 boys; mean age = 11.1 years [95% CI = 10.3, 11.8 years]).

MAIN OUTCOME MEASURE(S)

Player on-field head-impact exposure was captured using the Triax SIM-G system. We determined the accuracy between player and parent estimates relative to on-field head-impact exposures using κ and weighted κ values.

RESULTS

Youth tackle football players and parents did not accurately estimate on-field head-impact frequency (κ range = -0.09 to 0.40), severity (κ range = -0.05 to 0.34), or location (κ range = -0.30 to 0.13). Players and parents overestimated head-impact frequency in practices but underestimated the frequency in games. Both groups overestimated head-impact severity, particularly in games. Most players and parents underestimated the number of head impacts to the top of the head, particularly during practices.

CONCLUSIONS

Underestimations of head-impact frequency in games and to the top of the head suggest that informed consent processes aimed at educating players and parents should be improved. Overestimations of head-impact frequency in practices and severity may explain declining rates of youth tackle football participation.

Whitewater Helmet STAR: Evaluation of the Biomechanical Performance and Risk of Head Injury for Whitewater Helmets

More than six million people participate in whitewater kayaking and rafting in the United States each year. Unfortunately, with these six million whitewater participants come 50 deaths annually, making it one of the highest fatality rates of all sports. As the popularity in whitewater activities grows, the number of injuries, including concussions, also increases. The objective of this study was to create a new rating system for whitewater helmets by evaluating the biomechanical performance and risk of head injury of whitewater helmets using the Summation of Tests for the Analysis of Risk (STAR) system. All watersport helmets that passed the EN: 1385: 2012 standard and that were clearly marketed for whitewater use were selected for this study. Two samples of each helmet model were tested on a custom pendulum impactor under conditions known to be associated with the highest risk of head injury and death. A 50th percentile male NOCSAE headform instrumented with three linear accelerometers and a triaxial angular rate sensor coupled with a Hybrid III 50th percentile neck were used for data collection. A total of 126 tests were performed using six different configurations. These included impacts to the front, side, and rear using two speeds of 3.1 and 4.9 m/s that modeled whitewater river flow rates. Each helmet's STAR score was calculated using the combination of exposure and injury risk that was determined from the linear and rotational head accelerations. The resulting head impact accelerations predicted a very high risk of concussion for all impact locations at the 4.9 m/s speed. The STAR score varied between helmets indicating that some helmets provide better protection than others. Overall, these results show a clear need for improvement in whitewater helmets, and the methodologies developed in this research project should provide manufacturers a design tool for improving these products.

Assessing the validity of a helmet fit checklist in a sample of youth football players

The dynamics of American youth football make it critical to ensure that helmets are appropriately fit to decrease the risk of injuries. Currently, there is only one researcher-developed checklist to determine helmet fit, and psychometric testing is lacking; therefore, the aim of this work was to determine the validity of the checklist. The 13-item checklist was used to measure helmet fit in 267 youth football players prior to the start of the season. Using a Principal Components Analysis to assess validity, a 5-component model was found explaining 58% of the available variance. These results suggest that a single, summative score should not be used for this checklist; rather five scores should be calculated for each component (stability, snugness, size, integrity, and accessory). A more practical and valid tool to assess fit, such as a sub-sectioned chronological American football-specific checklist, can better assist coaches/administrators responsible for helmet fit and player safety.

Relationship Between Time-Weighted Head Impact Exposure on Directional Changes in Diffusion Imaging in Youth Football Players

Approximately 3.5 million youth and adolescents in the US play football, a sport with one of the highest rates of concussion. Repeated subconcussive head impact exposure (HIE) may lead to negative neurological sequelae. To understand HIE as an independent predictive variable, quantitative cumulative kinematic metrics have been developed to capture the volume (i.e., number), severity (i.e., magnitude), and frequency (i.e., time-weighting by the interval between head impacts). In this study, time-weighted cumulative HIE metrics were compared with directional changes in diffusion tensor imaging (DTI) metrics. Changes in DTI conducted on a per-season, per-player basis were assessed as a dependent variable. Directional changes were defined separately as increases and decreases in the number of abnormal voxels relative to non-contact sport controls. Biomechanical and imaging data from 117 athletes (average age 11.9 ± 1.0 years) enrolled in this study was analyzed. Cumulative HIE metrics were more strongly correlated with increases in abnormal voxels than decreases in abnormal voxels. Additionally, across DTI sub-measures, increases and decreases in mean diffusivity (MD) had the strongest relationships with HIE metrics (increases in MD: average R² = 0.1753, average p = 0.0002; decreases in MD: average R² = 0.0997, average p = 0.0073). This encourages further investigation into the physiological phenomena represented by directional changes.

Design and simulation of a PK testbed for head impact evaluation

This paper presents the design and simulation of a Parallel Kinematic (PK) testbed for head impacts. The proposed design is presented as a novel head impact testbed using a parallel platform as main motion simulation mechanism. The testbed is used to give a motion to a head mannequin to impact against a steel plate. In addition, the platform in the testbed allows to modify the orientation of the head mannequin model to evaluate different types of impacts. The testbed has been modeled with software MS ADAMS® to evaluate its performance with a dynamic simulation and to characterize the testbed design during top and lateral impact events. Results show that PK testbed gives a significant force and acceleration to the head mannequin at the moment of the impact.

Improper Fit in American Youth Football Helmets Across One Competitive Season

Improper helmet fit is related to sport-related concussion symptomology. The objective of this study was to determine the prevalence of improperly fit helmets in American youth tackle football players across one competitive season. Four recreation leagues including 147 players (45.2 ± 14.7 cm, 147.5 ± 9.0 kg), aged 7-12 years, participated in pre-season and post-season data collection timepoints. Participant and league demographics were collected at pre-season. Helmet fit was assessed at pre- and post-season using a 13-item checklist. A helmet was defined as improperly fit if failed to comply with or more of the checklist items. Most players (84%) rented helmets from the league. At preseason, 71.4% of helmets, and at post-season 79.6%, were improperly fit with no significant change over time (p = 0.14). Of the 105 improperly fit helmets at the start of the season, 61% were still considered improperly fit at post season. The 11-12 year old age group had significantly more improperly fit helmets than the 7-10 year old age group at post-season (p = 0.033), but not pre-season (p = 0.655). American youth football players depend on the league to fit their helmet. Most players did not meet at least one checklist criteria. Helmets improperly fit at preseason were still not fit at post.

A Review of On-Field Investigations into the Biomechanics of Concussion in Football and Translation to Head Injury Mitigation Strategies

This review paper summarizes the scientific advancements in the field of concussion biomechanics in American football throughout the past five decades. The focus is on-field biomechanical data collection, and the translation of that data to injury metrics and helmet evaluation. On-field data has been collected with video analysis for laboratory reconstructions or wearable head impact sensors. Concussion biomechanics have been studied across all levels of play, from youth to professional, which has allowed for comparison of head impact exposure and injury tolerance between different age groups. In general, head impact exposure and injury tolerance increase with increasing age. Average values for concussive head impact kinematics are lower for youth players in both linear and rotational acceleration. Head impact data from concussive and non-concussive events have been used to develop injury metrics and risk functions for use in protective equipment evaluation. These risk functions have been used to evaluate helmet performance for each level of play, showing substantial differences in the ability of different helmet models to reduce concussion risk. New advances in head impact sensor technology allow for biomechanical measurements in helmeted and non-helmeted sports for a more complete understanding of concussion tolerance in different demographics. These sensors along with advances in finite element modeling will lead to a better understanding of the mechanisms of injury and human tolerance to head impact.

Concussion Risk Between Individual Football Players: Survival Analysis of Recurrent Events and Non-events

Concussion tolerance and head impact exposure are highly variable among football players. Recent findings highlight that head impact data analyses need to be performed at the subject level. In this paper, we describe a method of characterizing concussion risk between individuals using a new survival analysis technique developed with real-world head impact data in mind. Our approach addresses the limitations and challenges seen in previous risk analyses of football head impact data. Specifically, this demonstrative analysis appropriately models risk for a combination of left-censored recurrent events (concussions) and right-censored recurrent non-events (head impacts without concussion). Furthermore, the analysis accounts for uneven impact sampling between players. In brief, we propose using the Consistent Threshold method to develop subject-specific risk curves and then determine average risk point estimates between subjects at injurious magnitude values. We describe an approach for selecting an optimal cumulative distribution function to model risk between subjects by minimizing injury prediction error. We illustrate that small differences in distribution fit can result in large predictive errors. Given the vast amounts of on-field data researchers are collecting across sports, this approach can be applied to develop population-specific risk curves that can ultimately inform interventions that reduce concussion incidence.