Football Helmet Research Articles

Does pad displacement correlate to impact severity metrics in football helmets?

As efforts to reduce sport-related head injuries continue, there is a need to better understand the mechanisms of an impact that influence the risk of sustaining a concussion. This study presents a method which can be used to separate football helmet pad displacement into normal and rotational components. Finite element models of three popular football helmets were used to simulate a variety of impacts per the National Football League (NFL) helmet testing protocol. Pad displacement components were evaluated for correlation with impact severity metrics including Head Injury Criterion (HIC), Diffuse Axonal Multi-Axis General Evaluation (DAMAGE), and Head Acceleration Response Metric (HARM). When combining all locations, displacement was not found to correlate well with severity metrics ( R2 < 0.44). However, trends did exist with normal displacement when evaluating data by impact location. Normal displacement was found to correlate strongly with HARM, HIC, and Peak Resultant Linear Acceleration (PRLA) at the side upper (SU) location ( R2 = 0.79–0.8). Overall, it was observed that helmets which maximize normal displacement without bottoming out performed better. Tangential displacement was not found to correlate well with any impact severity metrics even when evaluated by location. This study has provided a method to evaluate components of helmet pad normal displacement during simulations which may help guide design and optimization efforts for helmets under impact in critical locations.

Embedded finite element modeling of the mechanics of brain axonal fiber tracts under head impact conditions

Investigating and understanding the biomechanical kinematics and kinetics of human brain axonal fibers during head impact process is crucial to study the mechanisms of Traumatic Axonal Injury (TAI). Such a study may require the explicit incorporation of brain fiber tracts into the host brain in order to distinguish the mechanical states of axonal fibers and brain tissue. Herein we extend our previously developed human head model by using an embedded element method to include fiber tracts reconstructed from diffusion tensor images in a host brain with the purpose of numerically tracking the deformation state of axonal fiber tracts during a head impact simulation. The updated model is validated by comparing its prediction of intracranial pressures with experimental data, followed by a thorough study of the effects of element types used for fiber tracts and the stiffness ratios of fiber to host brain. The validated model is also used to predict and visualize the damaged region of fiber tracts during the head impact process based on different injury criteria. The model is promising in tracking the state of fiber tracts and can add more objective functions such as axonal fiber deformation if used in the future design optimization of head protective equipment such as a football helmet.

Biofidelity and Limitations of Instrumented Mouthguard Systems for Assessment of Rigid Body Head Kinematics.

Instrumented mouthguard systems (iMGs) are commonly used to study rigid body head kinematics across a variety of athletic environments. Previous work has found good fidelity for iMGs rigidly fixed to anthropomorphic test device (ATD) headforms when compared to reference systems, but few validation studies have focused on iMG performance in human cadaver heads. Here, we examine the performance of two boil-and-bite style iMGs in helmeted cadaver heads. Three unembalmed human cadaver heads were fitted with two instrumented boil-and-bite mouthguards [Prevent Biometrics and Diversified Technical Systems (DTS)] per manufacturer instructions. Reference sensors were rigidly fixed to each specimen. Specimens were fitted with a Riddell SpeedFlex American football helmet and impacted with a rigid impactor at three velocities and locations. All impact kinematics were compared at the head center of gravity. The Prevent iMG performed comparably to the reference system up to ~ 60g in linear acceleration, but overall had poor correlation (CCC = 0.39). Prevent iMG angular velocity and BrIC generally well correlated with the reference, while underestimating HIC and overestimating HIC duration. The DTS iMG consistently overestimated the reference across all measures, with linear acceleration error ranging from 10 to 66%, and angular acceleration errors greater than 300%. Neither iMG demonstrated consistent agreement with the reference system. While iMG validation efforts have utilized ATD testing, this study highlights the need for cadaver testing and validation of devices intended for use in-vivo, particularly when considering realistic (non-idealized) sensor-skull coupling, when accounting for interactions with the mandible and when subject-specific anatomy may affect device performance.

Influence of Long-Term Use of American Football Helmets on Concussion Risk.

In this study, to discuss the influence of concussion risk from the long-term use of American football helmets on collegiate teams, accident cases during the game are replicated based on game videos by simulations using whole-body numerical models and helmeted finite element human head models. The concussion risks caused by collisions were estimated using the mechanical parameters inside the skull obtained from finite element analyses. In the analyses, the different material properties of helmets identified by free-fall experiments using headform impactor-embedded helmets were used to represent brand-new and long-term-use helmets. After analyzing the five cases, it was observed that wearing a new helmet instead of a long-term-use one resulted in a reduction in the risk of concussion by 1 to 44%. More energy is attenuated by the deformation of the liners of the brand-new helmet, so the energy transferred to the head is smaller than that when wearing the long-term-use helmet. Thus, the long-term use of the helmet reduces its ability to protect the head.

Head Impact Exposure in Hawaiian High School Football: Influence of Adherence Rates on a Helmetless Tackling and Blocking Training Intervention.

High school football remains a popular, physically demanding sport despite the known risks for acute brain and neck injury. Impacts to the head also raise concerns about their cumulative effects and long-term health consequences. To examine the effectiveness of a helmetless tackling training program to reduce head impact exposure in football participants. A three-year, quasi-experimental, prospective cohort (clinicaltrials.gov #NCTXXX) study. Honolulu (XXX, XXX) area public and private secondary schools with varsity and junior varsity football. Football participants (n=496) ages 14 to 18 years old. Intervention(s) Participants wore new football helmets furnished with head impact sensor technology. Teams employed a season-long helmetless tackling and blocking intervention in Years 2 and 3 consisting of a 3-phase, systematic progression of 10 instructional drills. Head impact frequency per athlete exposure (ImpAE), location, and impact magnitude per participant intervention adherence levels (60% and 80%). An overall regression analysis revealed a significant negative association between ImpAE and adherence (p=0.003, beta=-1.21, SE=0.41). In year 3, a longitudinal data analysis of weekly ImpAE data resulted in an overall difference between the adherent and non-adherent groups (p=0.040 at 80%; p=0.004 at 60%), mainly due to decreases in top and side impacts. Mean cumulative impact burden for the adherent group (n=131: 2,105.84g ± 219.76,) was significantly (p=0.020) less than the non-adherent group (n=90: 3,158.25g ± 434.80) at the 60% adherence level. Participants adhering to the intervention on at least a 60% level experienced a 34% to 37% significant reduction in the number of head impacts (per exposure) through the season. These results provide additional evidence that a helmetless tackling and blocking training intervention (utilizing the HuTT® program) reduces head impact exposure in high school football players. Adherence to an intervention is crucial for achieving intended outcomes.

Modeling the thermoregulatory significance of differential solar absorptance in American football helmets

Modeling the thermoregulatory significance of differential solar absorptance in American football helmets

Impact Deceleration Differences on Natural Grass Versus Synthetic Turf High School Football Fields

American football has the highest rate of concussions in United States high school sports. Within American football, impact against the playing surface is the second-most common mechanism of injury. The objective of this study was to determine if there is a difference in impact deceleration between natural grass and synthetic turf high school football fields. A Century Body Opponent Bag (BOB) manikin was equipped with a Riddell football helmet and 3 accelerometers were placed on the forehead, apex of the head, and right ear. The manikin was dropped from a stationary position onto its front, back, and left side onto natural grass (n = 10) and synthetic turf (n = 9) outdoor football fields owned and maintained by public and private institutions on O‘ahu, Hawai‘i. Data was collected on 1,710 total drops. All accelerometers in forward and backward falls, and 1 accelerometer in side falls showed significantly greater impact deceleration on synthetic turf compared to the natural grass surfaces (P < .05). The results of this study provide evidence-based rationale to inform youth sports policies, particularly those aimed at injury prevention through safer playing environments and equipment.

IoT Integrated Accelerometer Design and Simulation for Smart Helmets

This article delves into the transformative potential of micro-electromechanical systems (MEMS) accelerometers, particularly their role in revolutionizing helmet safety. Accelerometers, ubiquitous in vehicle manufacturing, computer technology, and audio-video systems, play a crucial role in measuring acceleration. This work focuses on the design and simulation of a rotating accelerometer integrated into football helmets. The introduction of rotational acceleration addresses specific challenges in detecting and mitigating brain injuries that linear accelerometers may encounter. Additionally, the article explores the concept of piezoresistive football helmets, designed to resist force and reduce the impact of concussions. Piezoresistive helmets, designed to resist force and minimize the impact of concussions, when augmented with Internet of Things (IoT) capabilities can create a comprehensive smart safety solution. The incorporation of IoT sensors and connectivity into piezoresistive helmets enables real-time monitoring and data analysis of impact forces. This integration not only enhances player safety by providing immediate insights into potential risks but also opens avenues for injury prevention strategies. Leveraging COMSOL simulation software, this research not only conceives but also realizes the innovative integration of rotational accelerometers and piezoresistive materials in football helmet design, advancing safety standards in sports technology.

Novel Fiber-Based Padding Materials for Football Helmets

An experimental study is performed to determine the head mechanics of American football helmets equipped with novel fiber energy absorbing material (FEAM). FEAM-based padding materials have substrates of textile fabrics and foam made with nylon fibers using electro-static flocking process. Both linear and angular accelerations of the sport helmets are determined under impact loads using a custom-built linear impactor and instrumented head. The effectiveness of padding materials and vinyl nitrile (VN) foam for impact loads on six different head positions that simulate two helmeted sport athletes in real-time helmet-to-helmet strike/impact is investigated. A high-speed camera is used to record and track neck flexion angles and compare them with pad effectiveness to better understand the head kinematics of struck players at three different impact speeds (6 m/s, 8 m/s, and 10 m/s). At impact speed of 6 m/s and 8 m/s, the FEAM-based padding material of 60 denier fibers showed superior resistance for angular acceleration. Although novel pads of VN foam flocked with 60 denier fibers outperformed with lowest linear acceleration for most of the head positions at low impact speed of 6 m/s, VN foam with no fibers demonstrated excellent performance for linear acceleration at other two speeds.

Efficacy of Guardian Cap Soft-Shell Padding on Head Impact Kinematics in American Football: Pilot Findings.

Sport-related concussion prevention strategies in collision sports are a primary interest for sporting organizations and policy makers. After-market soft-shell padding purports to augment the protective capabilities of standard football helmets and to reduce head impact severity. We compared head impact kinematics [peak linear acceleration (PLA) and peak rotational acceleration (PRA)] in athletes wearing Guardian Cap soft-shell padding to teammates without soft-shell padding. Ten Division I college football players were enrolled [soft-shell padding (SHELL) included four defensive linemen and one tight end; non-soft-shell (CONTROL) included two offensive linemen, two defensive linemen, and one tight end]. Participants wore helmets equipped with the Head Impact Telemetry System to quantify PLA (g) and PRA (rad/s2) during 14 practices. Two-way ANOVAs were conducted to compare log-transformed PLA and PRA between groups across helmet location and gameplay characteristics. In total, 968 video-confirmed head impacts between SHELL (n = 421) and CONTROL (n = 547) were analyzed. We observed a Group x Stance interaction for PRA (F1,963 = 7.21; p = 0.007) indicating greater PRA by SHELL during 2-point stance and lower PRA during 3- or 4-point stances compared to CONTROL. There were no between-group main effects. Protective soft-shell padding did not reduce head impact kinematic outcomes among college football athletes.

American Football Soft-Shell Helmet Covers Reduce Head Impact Severity: A Critically Appraised Topic

Focused Clinical Question: Do soft-shell helmet covers reduce head impact severity in American football helmets? Clinical Bottom Line: There is consistent SORT level C evidence to support that soft-shell helmet covers reduce measures of head impact severity and measures of linear and rotational acceleration. The impact reductions occurred at magnitudes less than the average reported concussive impact, which limits the application of the evidence with respect to concussion incidence or risk among American football players.

Investigating the influence of head kinematics on head injury metrics and factors to consider for football helmet design

There is a need to understand the relationship between head kinematics, impact severity metrics, and overall helmet performance as sports-related concussions continue to be prevalent. This study evaluates these relationships, emphasizing newly developed severity metrics that consider both translational and rotational contributions. Impact tests were performed following the NFL testing protocol on four prominent football helmets. The resulting data was used to determine Head Acceleration Response Metric (HARM), Diffuse Axonal Multi-Axis General Evaluation (DAMAGE), and Head Injury Criterion (HIC). HARM scores, a combination of HIC and DAMAGE, were ultimately used to solve for a Helmet Performance Score. When analyzing all impacts, DAMAGE showed a stronger correlation to HARM than HIC ( R2 = 0.76 vs R2 = 0.57); however, the strongest correlation existed between peak resultant angular velocity (PRAV) and HARM ( R2 = 0.87). When examining impacts at only the side, side upper (SU), and oblique front (OF) locations grouped together, HIC demonstrated the strongest correlation to HARM in the study ( R2 = 0.96). PRAV was the best predictor for HARM over peak resultant linear acceleration (PRLA) and peak resultant angular acceleration for four of the six impact locations (C, D, FMCO, and FMS) when analyzing the sites individually. The remaining locations (SU and OF) best predicted HARM using PRLA. These results are presented and discussed to aid in the research, design, and development of football helmets.

Modal analysis of computational human brain dynamics during helmeted impacts

Sports-related mild traumatic brain injury (mTBI) is a growing public health concern, affecting millions in the U.S., annually. Current helmets are primarily designed to mitigate head kinematics, despite the importance of the brain substructures mechanics in mTBI mechanism. Therefore, it is crucial to consider the dynamical behavior of brain substructures, which has been shown in prior studies to be associated with strain concentration. Here, we studied the modal behavior and strain patterns of the substructures of the brain finite element (FE) model through Dynamic Mode Decomposition. We conducted side and front impact pendulum tests on a dummy headform equipped with hockey, football, ski, and bicycle helmets. After simulating the impact tests using a brain FE model, we calculated the dynamic modes of this computational model for the whole brain, corpus callosum, brainstem, and cerebellum. The main mode of oscillation in all regions for all helmet types occurred around the frequency regime of 7–15 Hz. Also, in cerebellum, a second harmonic was observed at 40–50 Hz in front impact, and 38 and 62 Hz in side impact in bicycle and ski helmets, respectively. Furthermore, we analyzed the correlation between the modal response and peak maximum principal strain (MPS). These analyses mostly showed a direct association between the computational modal behavior and MPS, where helmet tests with closely spaced modes and high-frequency modal amplitudes led to higher MPS values. This association between the computational modal behavior and strain patterns demonstrated a potential for improving helmet designs through a novel design objective.Statement of significance: Sport-related mild traumatic brain injury (mTBI), which is one of the leading cause of death, can be reduced in severity by using headgears including helmets. Despite the recent innovations and technologies in helmet design, there are important factors that still have been missed. While it’s been shown that the brain substructures mechanics play an important role in mTBI mechanism, current helmets are designed to only mitigate the head kinematics. Moreover, dynamical behavior of these substructures, and existence of multimodal behavior in the brain are factors that have not been addressed in designing helmets. This paper shows the effect of different helmet types on modal behavior of the brain substructures and how the dynamical modes of these regions can be affected by using various helmet types.

Softer Foam in Bicycle Helmets Reduces the Impact Force in a Simulation Model

Objective: This study compared the linear acceleration generated from an impact to a manikin's head wearing an off-the -shelf “standard” bicycle helmet (stdBH) compared to a modified bicycle helmet (modBH) (original foam replaced with softer polyolefin foam). Methods: Pairs of 5 different bicycle helmets from a wide price range ($20-$90) were tested (standard versus modified). The head impact was simulated by striking the test bicycle helmet placed onto the head of a Century BOB boxing manikin, with a conventional football helmet (4.6 kg additional weight added) swung from a 1.2 meter rope and released from an angle of 45º serially for multiple data points as in Figure 2. The manikin's bicycle helmet was struck by the football helmet in the frontal, left parietal, and occipital locations for 12 trials each. Each of three accelerometers located at the manikin’s forehead, apex of the head, and right ear collected data on linear acceleration in the X, Y, and Z planes. Results: Mean linear acceleration in G's (9.8 m/sec/sec) was obtained from the three accelerometer locations on the manikin's head for each striking position. The mean linear accelerations across the 5 different helmet pairs are summarized in the graphs (Figure 3). For each of the three striking locations, there were statistically lower striking forces sustained with the modified softer foam bicycle helmet (modBH) compared to the standard bicycle helmet (stdBH). The greatest reductions were observed in the apical accelerometers when the manikin was struck from the occipital and parietal locations. Conclusion: These results suggest that softer foams in bicycle helmets may reduce injury from bicycle accidents. Further research on this topic can lead to the development of safer and more effective bicycle helmets.

Helmet Fitting: One Size Does NOT Fit All!

Coaches play an important role in ensuring that safety measures, including proper helmet fit, are practiced in youth and high school football. If proper guidelines and safety checks are adhered to, helmets will function as they are intended for in injury prevention and protection. Studies have shown that approximately 84% of youth and high school football helmets are improperly fitted, thus demonstrating the need for continued education and increased competency among novice and seasoned coaches to meet the guidelines and standards for proper fit. The purpose of this article is to (1) provide an infographic as a quick reference guide that can be used to assist coaches and players in remembering the steps of how to size, check, fit, stress and recheck a helmet and (2) demonstrate the minimum criteria coaches need to proficiently implement to properly fit a helmet so best practices toward greater safety can be achieved in youth and high school football.

Leveraging football accelerometer data to quantify associations between repetitive head impacts and chronic traumatic encephalopathy in males

Chronic traumatic encephalopathy (CTE) is a neurodegenerative tauopathy associated with repetitive head impacts (RHI), but the components of RHI exposure underlying this relationship are unclear. We create a position exposure matrix (PEM), composed of American football helmet sensor data, summarized from literature review by player position and level of play. Using this PEM, we estimate measures of lifetime RHI exposure for a separate cohort of 631 football playing brain donors. Separate models examine the relationship between CTE pathology and players’ concussion count, athletic positions, years of football, and PEM-derived measures, including estimated cumulative head impacts, linear accelerations, and rotational accelerations. Only duration of play and PEM-derived measures are significantly associated with CTE pathology. Models incorporating cumulative linear or rotational acceleration have better model fit and are better predictors of CTE pathology than duration of play or cumulative head impacts alone. These findings implicate cumulative head impact intensity in CTE pathogenesis.

Finite element evaluation of an American football helmet featuring liquid shock absorbers for protecting against concussive and subconcussive head impacts.

Introduction: Concern has grown over the potential long-term effects of repeated head impacts and concussions in American football. Recent advances in impact engineering have yielded the development of soft, collapsible, liquid shock absorbers, which have demonstrated the ability to dramatically attenuate impact forces relative to existing helmet shock absorbers. Methods: To further explore how liquid shock absorbers can improve the efficacy of an American football helmet, we developed and optimized a finite element (FE) helmet model including 21 liquid shock absorbers spread out throughout the helmet. Using FE models of an anthropomorphic test headform and linear impactor, a previously published impact test protocol representative of concussive National Football League impacts (six impact locations, three velocities) was performed on the liquid FE helmet model and four existing FE helmet models. We also evaluated the helmets at three lower impact velocities representative of subconcussive football impacts. Head kinematics were recorded for each impact and used to compute the Head Acceleration Response Metric (HARM), a metric factoring in both linear and angular head kinematics and used to evaluate helmet performance. The head kinematics were also input to a FE model of the head and brain to calculate the resulting brain strain from each impact. Results: The liquid helmet model yielded the lowest value of HARM at 33 of the 36 impact conditions, offering an average 33.0% (range: -37.5% to 56.0%) and 32.0% (range: -2.2% to 50.5%) reduction over the existing helmet models at each impact condition in the subconcussive and concussive tests, respectively. The liquid helmet had a Helmet Performance Score (calculated using a summation of HARM values weighted based on injury incidence data) of 0.71, compared to scores ranging from 1.07 - 1.21 from the other four FE helmet models. Resulting brain strains were also lower in the liquid helmet. Discussion: The results of this study demonstrate the promising ability of liquid shock absorbers to improve helmet safety performance and encourage the development of physical prototypes of helmets featuring this technology. The implications of the observed reductions on brain injury risk are discussed.

Impact attenuation capabilities of new and used football helmets

Football helmets are expected to break down with use, and reconditioning recommendations are required to be stated by manufacturers. However, the degree of change in helmet impact mitigation performance as a function of usage is not generally known. Therefore, this study aimed to compare the ability of football helmets to attenuate impacts after a single season of regular collegiate use to unused helmets. Three never-used Riddell® Speed™ helmets were tested and compared to three used helmets which had been used during one season of Division 1 collegiate football. Helmets were tested at three velocities (3.46, 4.88, and 5.46 m s−1) on six locations in ambient temperature, simulating National Operating Committee on Standards for Athletic Equipment certification drop tests. The interaction between helmet age and location during all three velocities (P 0.0001), indicating that there were differences in Gadd severity index (GSI) between new and used helmets after accounting for location-specific differences. Similar analysis for peak linear acceleration (PLA) found significant interactions for all three velocities (P 0.003). Additional analyses found differences in velocity-dependence for several impact locations. In most cases, used helmets yielded lower GSI and PLA relative to new helmets. The reduction in impact metrics for used helmets indicates initial break-in with impact mitigation benefits, but the long-term consequences of continued use are unclear. The implications of these differences on injury risk and susceptibility remain unknown; however, the results suggest that further studies could inform helmet reconditioning guidelines and development of new smart materials designed to monitor and/or prevent breakdown in padding.

Commentary: Comparing Impact and Concussion Risk in Leatherhead and Modern Football and Hockey Helmets.

Jonzzon, Soren MD*,‡; Jo, Jacob BA*,‡; Zuckerman, Scott L. MD, MPH*,‡ Author Information

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Study explores protection provided by football helmets Survey looks into problems caused by NIL Women coaches, administrators remain underrepresented