Brain injury prediction: assessing the combined probability of concussion using linear and rotational head acceleration

Ability of Head Impact Measurements to Predict Sports Concussions: A Review

BACKGROUND AND OBJECTIVES

Provide a review of the current landscape of motion sensor-based analyses of mild traumatic brain injury (concussion) and shed light on avenues for further investigation.

METHODS

A review of the literature on motion sensor-based concussion studies was conducted using search terms "concussion prediction sensor," "concussion prediction motion," "concussion diagnosis sensor," and "concussion diagnosis motion" in PubMed (between January 2000 and March 2024). In total, 207 publications were initially identified. However, only 14 studies were ultimately included, due to lack of requisite measurement variables, focus on different outcomes, or participant overlap with included studies. Consolidation of mean and standard deviation of measurement variables was performed using the application of Cochrane formula.

RESULTS

Across 14 studies, most used head impact data from football (85.7%) and the Head Impact Telemetry system for data acquisition (92.9%). Most of the studies used data sets from collegiate athletes (71.4%). A minority of studies included female athletes (14.3%). On average, male athletes experienced higher linear and rotational accelerations during concussive vs nonconcussive impacts (97.6 ± 33.8 g and 4614.9 ± 2568.7 rad/s2 vs 24.4 ± 16.2 g and 1641.9 ± 1216.6 rad/s2). Moreover, male athletes experienced higher linear accelerations, but similar rotational accelerations, compared with female athletes specifically during concussive impacts (97.6 ± 33.8 g and 4614.9 ± 2568.7 rad/s2 vs 43.0 ± 11.5 g and 4030 ± 1435 rad/s2). Notably, studies that predicted concussion probability using multivariate regression methods (26.7%) demonstrated challenges with accuracy due to low positive predictive values (ranging from 0.3%-0.9%) and high false-positive rates (up to 39.4%).

CONCLUSION

Despite the statistical differences in head impact measurements between concussive and nonconcussive impacts, they have limited clinical utility as a stand-alone concussion identification tool. Head impact measurements may be most useful when used as an adjunct to other clinical and physiological markers.

Combining evidence and practice to optimise neck training aimed at reducing head acceleration events in sport: a systematic review and Delphi-consensus study

Head acceleration events (HAEs) can potentially have adverse consequences for athlete brain health. In sports, in which head injuries have the highest incidence, identifying strategies to reduce HAE frequency and magnitude is a priority. Neck training is a potential strategy to mitigate against the magnitude of HAEs. This two-part study aimed to (1) systematically review the literature of neck training interventions in sport and (2) undertake an expert Delphi consensus on the best practices for neck training implementation to reduce HAEs in sport. Part I: a systematic search of four databases was undertaken from the earliest records to September 2024. The PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis) guidelines were followed, and a quality assessment was completed using a modified Downs and Black assessment tool and the GRADE (Grading of Recommendations Assessment, Development and Evaluation). Papers were eligible if they both (1) implemented a reproducible exercise intervention targeting the neck within collision, combat or motor sport, and (2) assessed outcomes relating to either: the physical profile of the neck; head/neck injury incidence; and/or HAEs. Part II: 18 international experts, with experience in research and/or applied practice of neck exercise training, concussion and/or HAEs, reviewed the part I findings before completing a three-round Delphi consensus process. Part I included 21 papers, highlighting the heterogeneity of existing interventions. Part II resulted in 57 statements coded into five categories: contextual factors (n=17), neck training periodisation (n=12), training adaptations (n=10), neck training content (n=15) and athlete adherence (n=3). This study presents recommendations for neck exercise training aiming to reduce HAEs in sport, supporting both practice and future research.

Correlating Magnetoencephalography, Diffusion Kurtosis Imaging, Biomechanics, and Neuropsychology in American Youth Football

This study investigated the association between repetitive head impacts (RHIs) and multimodal neuroimaging, biomechanical, and neuropsychological data in 72 youth football players and 17 controls, aged 8-12 years. Helmet sensors measured RHI exposure while imaging and psychological data were collected before and after the season. Risk-weighted exposure metrics were calculated to quantify cumulative RHI exposure. Changes in magnetoencephalography (MEG) and diffusion kurtosis imaging were analyzed by calculating voxel-wise difference, and z-score maps were thresholded with respect to controls. Using linear regression, statistically significant positive associations were observed between abnormally increased MEG-measured theta (5-7 Hz) power and RHI measures. No associations were found between RHI and other neuroimaging metrics. Football players and controls exhibited significant yet divergent associations between alpha (8-12 Hz) power as well as mean kurtosis and neuropsychological changes. These findings indicate a potential association between youth football players' exposure to RHI and neurophysiological alterations.

Kinematic Insights Into Older Adult Fall-Related Head Impacts: Boundary Conditions and Injury Risk

OBJECTIVES

To quantify real-world impact conditions of falls, which cause 50% to 90% of older adult traumatic brain injuries, and reconstruct them using dummy headforms to analyze kinematics and injury outcomes.

DESIGN

Mixed-methods: Observational and experimental.

SETTING AND PARTICIPANTS

An open-access dataset of 118 videos of head impacts at long-term care facilities was used.

METHODS

Videos were analyzed to determine head impact occurrence, and for each video with a head impact, fall characteristics were recorded. Perpendicular view fall videos were analyzed using validated model-based image-matching software to track head impact velocities. From the tracked videos, falls were reconstructed with a Hybrid III headform mounted on an inverted pendulum to capture impact kinematics.

RESULTS

Of the 118 fall videos with head impacts, we tracked 29 videos, finding a normal velocity of 1.76 ± 1.02 m/s and a tangential velocity of 1.27 ± 0.95 m/s. Twenty-three of these impacts were reconstructed, producing peak linear acceleration (PLA) 50.2 ± 36.4 g and peak rotational acceleration (PRA) 2.91 ± 2.16 krad/s2. Impacts that occurred against the floor had a 38% higher PLA and a 25% higher PRA compared with wall impacts. Compared with backward and forward falls, lateral falls resulted in 46 and 52 g higher PLA and 3.12 and 4.66 krad/s2 higher PRA, respectively.

CONCLUSIONS AND IMPLICATION

Fall direction and impact surface influenced head impact accelerations, with certain fall configurations, such as lateral falls against tile, posing a greater risk for traumatic brain injuries. These findings provide critical insights into the biomechanics of older adult head impact falls and highlight the need for targeted fall prevention strategies, such as interventions that reduce the occurrence of lateral falls. In addition, this work offers foundational data for designing protective equipment, including headgear and energy-absorbing flooring, optimized for these specific kinematics.

Head Kinematics Associated with Off-Field Head Injury Assessment (HIA1) Events in a Season of English Elite-Level Club Men's and Women's Rugby Union Matches

OBJECTIVES

The purpose of this study was to investigate head kinematic variables in elite men's and women's rugby union and their ability to predict player removal for an off-field (HIA1) head injury assessment.

METHODS

Instrumented mouthguard (iMG) data were collected for 250 men and 132 women from 1865 and 807 player-matches, respectively, and synchronised to video-coded match footage. Head peak resultant linear acceleration (PLA), peak resultant angular acceleration (PAA) and peak change in angular velocity (dPAV) were extracted from each head acceleration event (HAE). HAEs were linked to documented HIA1 events, with ten logistical regression models for men and women, using a random subset of non-case HAEs, calculated to identify kinematic variables associated with HIA1 events. Receiver operating characteristic curves (ROC) were used to describe thresholds for HIA1 removal.

RESULTS

Increases in PLA and dPAV were significantly associated with an increasing likelihood of HIA1 removal in the men's game, with an OR ranging from 1.05-1.12 and 1.13-1.18, respectively. The optimal values to maximise for both sensitivity and specificity for detecting an HIA1 were 1.96 krad⋅s-2, 24.29 g and 14.75 rad⋅s-1 for PAA, PLA and dPAV, respectively. Only one model had any significant variable associated with increasing the likelihood of a HIA1 removal in the women's game-PAA with an OR of 8.51 (1.23-58.66). The optimal values for sensitivity and specificity for women were 2.01 krad⋅s-2, 25.98 g and 15.38 rad⋅s-1 for PAA, PLA and dPAV, respectively.

CONCLUSION

PLA and dPAV were predictive of men's HIA1 events. Further HIA1 data are needed to understand the role of head kinematic variables in the women's game. The calculated spectrum of sensitivity and specificity of iMG alerts for HIA1 removals in men and women present a starting point for further discussion about using iMGs as an additional trigger in the existing HIA process.

Comparison of Instrumented Mouthguard Post-Processing Methods

Instrumented head acceleration measurement devices are commonly used in research studies to determine head acceleration exposure in certain populations. Instrumented mouthguards pair directly to the user's teeth and offer six-degree-of-freedom measurements. Though many studies have recently used these devices, post-processing techniques vary by study. Other studies have attempted to label impact quality or coupling status, also with varying methods. This study sought to compare the effect of post-processing and labeling methods on reported exposure distribution characteristics in instrumented mouthguard data from ice hockey players. We collected data from 18 female adolescent ice hockey players on two teams for an entire season. We then post-processed the measured signals using five different techniques: (1) the instrumented mouthguard manufacturer's data output, (2) a 500 Hz linear acceleration filter and a 300 Hz angular velocity filter, (3) HEADSport, (4) a 100 Hz linear acceleration filter and a 175 Hz angular velocity filter, and (5) a salvaging process to detect and remove decoupling based on signal frequency content. The post-processing techniques affected the reported exposure distributions by changing the mean, median, and 95th percentile values of peak linear and angular kinematics. We also compared labeling techniques by measuring agreement and inter-rater reliability between three labeling techniques: the instrumented mouthguard manufacturer's label, Luke et al.'s coupling label, and our classification learner that detects and labels decoupling. We found that the labeling techniques had low agreement about which acceleration events were the best to keep. Labeling technique also influenced the reported distributions' descriptive statistics. Post-processing and event labeling are crucial components of head acceleration event exposure studies. Methods should be described by researchers, and standardization should be sought to allow for better cross-study comparison. Published and publicly available techniques can help move the field toward this ideal. Researchers should be aware of the potential effect post-processing can have on a population's final reported exposure metrics.

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.

The biomechanical injury calculator: a postprocessor software for a finite element human body model

An injury risk assessment postprocessor for the Global Human Body Model Consortium (GHBMC) model is presented. The Biomechanical Injury Calculator (BIC) calculates injury probabilities for the head, neck, spine, and pelvis post-simulation, along with a total injury probability for the entire complex. It also generates an injury heatmap. Developed for the GHBMC M50-OS v2.3 +DeformSpine, BIC was validated by comparing 103 airmen's seat ejection injuries to BIC-predicted injury probabilities in 30 vertical seat load simulations. Observed injury rates correlated strongly with BIC predictions (Spearman=0.943, Pearson=0.982) within 5.16% margin. The total injury probability of 58.48% closely matched the 56.3% observed rate.

Evaluating Polo Helmet Performance Across Different Impact Test Systems

PURPOSE

This study evaluated head impact response between different helmet impact test systems by comparing the performance of ten polo helmets.

METHODS

Helmets were evaluated using three test systems: a twin-wire guided drop tower, an oblique drop tower, and an impact pendulum. Impact tests were conducted at matched locations (front boss, side, rear boss) and speeds (3.46, 5.46 m/s). We employed a linear mixed model with helmet model as a random effect and calculated the least square mean differences between systems for peak linear acceleration (PLA), peak rotational acceleration (PRA), peak rotational velocity (PRV), and concussion risk. Correlations between systems by impact speed were explored, using linear models of each system as a function of the others, and calculated Spearman rank correlation coefficients between test systems for each dependent variable.

RESULTS

Our results found distinct differences in PRA and concussion risk between the oblique and the pendulum impact systems due to the driving force. The acceleration range across helmet models was substantial, and responses differed between test systems at matched impact conditions. However, there were similarities between test systems in the rank order of helmet models. Head acceleration differences between helmets translated to larger differences in concussion risk between helmet models.

CONCLUSION

These trends provide a framework for comparing the headform's response across varying loading conditions. When selecting a test system to evaluate helmets for a specific sport, it is essential to consider the relevant impact conditions and loading patterns to ensure that laboratory tests accurately represent real-world scenarios.

Concussion injuries in sports and the role of instrumented mouthguards: a mini review

Contact sports such as American football, rugby, soccer, and ice hockey involve high-speed, high-impact interactions that frequently result in head acceleration events (HAEs), which can lead to concussions and other forms of traumatic brain injury. HAEs can lead to acute symptoms like dizziness and memory difficulties, as well as more severe, chronic conditions like cognitive decline and chronic traumatic encephalopathy. This mini-review focuses on concussion-related injuries in contact sports, examining their prevalence, impact, and the role of innovative prevention strategies. Particular attention is given to the development of instrumented mouthguards (iMGs), which incorporate real-time sensors to measure and analyze head impacts. Ultimately, this review aims to provide an overview of the role of iMGs on concussion prevention and its evolving landscape, with a focus on the potential of iMG technology.

Exploring Sex-Based Variations in Head Kinematics During Soccer Heading

While studies indicate that females experience a higher concussion risk and more severe outcomes in soccer heading compared to males, comprehensive data on the underlying factors contributing to these sex-based differences are lacking. This study investigates the sex differences in the head-to-ball impact kinematics among college-aged soccer headers in a laboratory-controlled setting. Forty subjects (20 females, 20 males) performed ten headers, and impact kinematics, including peak angular acceleration and velocity (PAA, PAV) and peak linear acceleration (PLA), were measured using mouthguards. Video recordings verified impacts and impact locations. Participants' head mass was estimated from their weights. The relationship between head mass and kinematic parameters was analyzed using Pearson correlation. The effects of head mass, sex, and impact location on kinematic parameters were assessed using MANOVA with and without head mass as a covariate. Results showed that head mass, larger in males than females, significantly affects PAA and PLA, the greater the head mass, the lower PAA and PLA. However, head mass has no effect on PAV. Females showed significantly higher PAA and PLA components but no significant differences in PAV. Impact location significantly influenced PAV, showing higher magnitudes for frontal impacts compared to top-front impacts, with no significant effects on PAA and PLA. Our results agree with epidemiological evidence that female soccer players face greater concussion risks than males, which can be attributed to their higher header-induced PAA. Future research could consider interventions like changing ball pressure, using protective headgear, and improving heading techniques to reduce high-magnitude accelerations in females.

An Evaluation of the Balance Error Scoring System in Female Soccer Players Following Soccer Heading: A Pilot Study

Background

Soccer is a contact sport during which participants risk injury, including due to concussion. Interestingly, the task most frequently associated with concussions is the act of heading the ball. This study seeks to answer the following research question: Does an acute playing of purposeful soccer heading in female football players lead to changes in BESS normative outcomes and balance? Additionally, we aim to explore the relationship between a gold-standard BESS Test and a Balance Test performed on a force plate.

Methods

This project involved twenty-eight female soccer players (age = 19.6 + 2.96 years, mass = 60.4+ 5.3 kg, and height = 163.6 + 6.4 cm). pre and post the heading condition and the results of the Wilcoxon Signed Ranks Test. The participants were healthy and underwent BESS monitoring on a force plate before and after heading and footing training. Standard 450 g soccer balls were utilized. Participants performed ten headers for the header condition and ten footers for the footer condition. Resultant sway velocity and BESS error outcomes were calculated before and after heading and footing training. I need a brief description of the statistical approach here.

Results

Statistically significant increases after the heading condition were found for Single Leg Stance (COP PATH) score (Z = -3.986, p = 0.000), BESS score on foam surface (Z = -2.511, p = 0.012), BESS score on firm surface (Z = -2.353, p = 0.019). A statistically significant increase after the footer condition was found for the Tandem Stance (mm2) score (Z = -2.900, p = 0.004). A statistically significant difference between the group conditions was found in the post-BESS score foam difference (U = 268.500, p = 0.042). BESS score foam mean increase was 1.93 after the heading condition and 0.21 after the footer condition.

Conclusion

This pilot study not only tests the feasibility of using force plates to measure BESS outcomes after heading in female soccer but also underscores the effectiveness of using BESS parameters to evaluate changes in balance function following heading compared to a control footer condition. The findings of this study provide valuable insights into the potential effects of soccer on balance in female players, contributing to the body of knowledge in sports medicine and physical education.

Level of evidence

3.

Performance of current tools used for on-the-day assessment and diagnosis of mild traumatic brain injury in sport: a systematic review

Objective

The monitoring and diagnosis of sports-related mild traumatic brain injury (SR-mTBI) remains a challenge. This systematic review summarises the current monitoring tools used for on-the-day assessment and diagnosis of SR-mTBI and their performance.

Design

Systematic review, using Quality Assessment of Diagnostic Accuracy Studies assessment.

Data sources

Embase via Ovid, IEEEXplore, Medline via Ovid, Scopus and Web of Science were searched up to June 2024.

Eligibility criteria

Peer-reviewed English-language journal articles which measured athletes using the index test within a day of injury and provided a performance measure for the method used. Studies of all designs were accepted, and no reference methods were required.

Results

2534 unique records were retrieved, with 52 reports included in the review. Participants were 76% male, when reported, and the mean injury-to-measurement time was reported in 10% of reports. 46 different methods were investigated. 38 different reference methods were used, highlighting the lack of gold standard within the field. Area under the curve (AUC), sensitivity and specificity were the most frequent outcome metrics provided. The most frequent index test was the King-Devick (KD) test. However, there were large variations in accuracy metrics between reports for the KD test, for instance, the range of AUC: 0.51-0.92.

Conclusion

Combinations of existing methods and the KD test were most accurate in assessing SR-mTBI, despite the inconsistent accuracy values related to the KD test. The absence of a gold-standard measurement hampers our ability to diagnose or monitor SR-mTBI. Further exploration of the mechanisms and time-dependent pathophysiology of SR-mTBI could result in more targeted diagnostic and monitoring techniques. The Podium Institute for Sports Medicine and Technology funded this work.

PROSPERO registration number

CRD42022376560.

Estimating Brain Injury Risk from Shipborne Underwater Blasts Using a High-fidelity Finite Element Head Model

INTRODUCTION

Assessing the survivability of, and potential injury to, a ship's crew from underwater blast is crucial to understanding the operating capability of a military vessel following blast exposure. One form of injury that can occur and affect a crew member's ability to perform tasks is traumatic brain injury (TBI). To evaluate the risk of TBI from underwater blasts, injury metrics based on linear head acceleration have traditionally been used. Although these metrics are popular given their ease of use, they do not provide a direct measure of the tissue-level biomechanical responses that have been shown to cause neuronal injury. Tissue-based metrics of injury, on the other hand, may provide more insight into the potential risk of brain injury. Therefore, in this study, we assess the risk of TBI from underwater blasts using tissue-based measures of injury, such as tissue strain, strain rate, and intracranial pressure, in addition to the more commonly used head acceleration-based injury metrics.

MATERIALS AND METHODS

A series of computational simulations were performed using a detailed finite element (FE) head model to study how inertial loading of the head from underwater blast events translates to potential injury in the brain. The head kinematics loading conditions for the simulations were obtained directly from Floating Shock Platform (FSP) tests where 3 Anthropomorphic Test Devices (ATDs) were positioned at 3 shipboard locations (desk, bulkhead, and bench), and the head acceleration was directly measured. The effect of the position and orientation of the ATDs and the distance of the underwater blast from the FSP (20-50 ft) on the risk of brain injury were assessed from the FE analysis.

RESULTS

The head accelerations and estimated TBI risk from the underwater blasts highly depend on the positioning of the ATDs on the FSP and decrease in severity as the charge standoff distance is increased. The ATD that was seated at a desk had the largest peak linear head acceleration (77.5 g) and negative intracranial pressure (-51.8 kPa). In contrast, the ATD that was standing at a bulkhead had the largest computed 95th percentile maximum principal strain (19%) and strain rate (25 s-1) in the brain. For all tested conditions, none of the ATDs exceeded the Head Injury Criterion (HIC-15) threshold of 700 for serious or fatal brain injury; however, the predicted tissue strains of the bulkhead ATD at the 20-ft charge standoff distance were within the range of proposed strain thresholds for a 50% risk of concussive injury, which illustrates the added value of considering tissue-level measures in addition to head acceleration when evaluating brain injury risk.

CONCLUSIONS

In this work, we assessed the risk of brain injury from underwater blasts using an anatomically detailed subject-specific FE head model. Accurate assessment of the risk of TBI from underwater explosions is important to evaluate the potential injury risk to crew members from underwater blast events, and to guide the development of future injury mitigation strategies to maintain the safety of crew members on military ships.

A cellulosic fibre foam as a bicycle helmet impact liner for brain injury mitigation in oblique impacts

Bulky cellulosic network structures (BRC) with densities between 60 and 130 g/l were investigated as a sustainable alternative to fossil-based foams for impact liners in bicycle helmets. The mechanical properties of BRC foams were characterized across a wide range of strain rates and incorporated into a validated finite element model of a hardshell helmet. Virtual impact tests simulating both consumer information and certification scenarios were conducted to compare BRC-lined helmets against conventional expanded polystyrene (EPS) designs. Results showed that BRC outperformed EPS in oblique impacts, reducing angular accelerations and velocity changes by approximately 33 %, particularly for z-axis rotations. The average risk of sustaining AIS2 injuries and concussions was lower for BRC (8 % and 34 % respectively) compared to EPS (13 % and 46 %). However, BRC helmets exhibited bottoming out in certain straight impacts, potentially failing certification tests. This limitation was addressed through design modifications. The study demonstrates that cellulosic fibre network structures have the potential to replace fossil-based foams in bicycle helmets while providing adequate protection and improved performance in mitigating rotational forces.

Position-based assessment of head impact frequency, severity, type, and location in high school American football

Introduction

Research on head impact characteristics, especially position-specific investigations in football, has predominantly focused on collegiate and professional levels, leaving a gap in understanding the risks faced by high school players. Therefore, this study aimed to investigate the effect of three factors-player position, impact location, and impact type-on the frequency, severity, and characteristics of impacts in high school American football. Additionally, we examined whether and how player position influences the distribution of impact locations and types.

Methods

Sixteen high school football players aged 14 to 17 participated in this study. Validated mouthguard sensors measured head impact kinematics, including linear acceleration, angular acceleration, and angular velocity across ten games, and were used to identify impact locations on the head. Video recordings verified true impacts, player position, and impact type at the moment of each recorded impact. Head impact kinematics were input into a head finite element model to determine the 95th percentile of the maximum principal strain and strain rate. Several novel and systematic approaches, such as normalization, binning, and clustering, were introduced and utilized to investigate the frequency and severity of head impacts across the three aforementioned factors while addressing some of the limitations of previous methodologies in the field. To that end, the number of recorded impacts for each player position during each game was divided by the number of players in that position, and then averaged across ten games. Instead of averaging, impacts were categorized into four severity bins: low, mid-low, mid-high and high. Clusters for the three factors were also identified according to the characteristics of impacts.

Results and Discussion

Results revealed that offensive linemen and running backs experienced a higher normalized frequency and more severe impacts across all head kinematics and brain tissue deformation parameters. Frontal impacts, resulting from "head-to-head" impacts, were the most frequent and severe impact locations. The distributions of impact location and type for each specific position were distinct. Offensive linemen had the highest proportion of frontal impacts, while quarterbacks and centerbacks had more impacts at the rear location. These findings can inform interventions in game regulations, training practices, and helmet design to mitigate injury risks in high school football.

Head kinematics of human subjects during laboratory-induced ladder falls to the ground

INTRODUCTION

Fall-induced traumatic brain injury (TBI) is considered one of the most serious occupational injuries in construction. Given the frequency of falls from ladders, knowledge of head kinematics during ladder falls to the ground may help inform any potential improvement to construction safety helmet design and improve their protection against head injury. Therefore, the goal of this descriptive study was to measure head kinematics during laboratory-induced ladder falls to the ground.

METHOD

Eighteen young adults wearing a hockey helmet simulated construction tasks that challenged their balance while standing on stepladders and an extension ladder with their feet at heights up to 1.8 m above padding covering the ground. Falls onto the padding occurred spontaneously or were induced by an investigator nudging the ladder to simulate ladder movement resulting from the ground shifting. Optoelectronic motion capture was used to capture head kinematics up to the instant immediately before head impact.

RESULTS

Of 115 total falls, 15 involved head impact with the padding and were analyzed. Head impact during all 15 of these falls occurred on the back of the head. Immediately before impact with the padding, head vertical velocity ranged from 0.42 to 3.88 m/s and head angular velocity about a medial-lateral axis ranged from 60.1 to 1215.5 deg/s.

CONCLUSIONS

These data can be used with computer simulations or headform impact testing to estimate true head impact kinematics, or to inform future versions of construction safety helmet testing standards.

PRACTICAL APPLICATIONS

This is the first study we are aware of to capture head kinematics of human subjects during ladder falls to the ground. These results have the potential to inform future versions of construction safety helmet testing standards and contribute to improved helmet design for protection against fall-induced head injury.

Concussion biomechanics, head acceleration exposure and brain injury criteria in sport: a review

There are mounting concerns surrounding the risk of neurodegenerative diseases and complications associated with concussion incidence and repetitive head acceleration events (HAE) in sport. The aim of this review is to provide an overview of concussion biomechanics, head acceleration exposure and brain injury criteria in sport. Rotational head motion appears to be the primary contributor to brain injury risk due to the unique mechanical properties of the brain and its location within the body. There is a growing evidence base of different biomechanical brain injury mechanisms, including those involving repetitive HAE. Historically, many studies on concussion biomechanics, head acceleration exposure and brain injury criteria in sport have been limited by validity of the biomechanical approaches undertaken. Biomechanical approaches such as instrumented mouthguards and subject-specific finite element (FE) brain models provide a unique opportunity to develop greater brain injury criteria and aid in on-field athlete removal. Implementing these approaches on a large-scale can gain insight into potential risk factors within sports and certain athletes/cohorts who sustain a greater number and/or severity of HAE throughout their playing career. These findings could play a key role in the development of concussion prevention strategies and techniques that mitigate the severity of HAE in sport.

How Shell Add-On Products Influence Varsity Football Helmet Performance?

PURPOSE

The study purpose was to investigate the laboratory-based performance of three commercially available shell add-on products under varsity-level impact conditions.

METHODS

Pendulum impact tests were conducted at multiple locations (front, front boss, rear, side) and speeds (3.1, 4.9, 6.4 m/s) using two helmet models. Tests were performed with a single add-on configuration for baseline comparisons and a double add-on configuration to simulate collisions with both players wearing shell add-ons. A linear mixed-effect model was used to evaluate peak linear acceleration (PLA), peak rotational acceleration (PRA), and concussion risk, which was calculated from a bivariate injury risk function, based on shell add-on and test configuration.

RESULTS

All shell add-ons decreased peak head kinematics and injury risk compared to controls, with the Guardian NXT producing the largest reductions (PLA: 7.9%, PRA: 14.1%, Risk: 34.1%) compared to the SAFR Helmet Cover (PLA: 4.5%, PRA: 9.3%, Risk: 24.7%) and Guardian XT (PLA: 3.2%, PRA: 5.0%, Risk: 15.5%). The same trend was observed in the double add-on test configuration. However, the Guardian NXT (PLA: 17.1%; PRA: 11.5%; Risk: 62.8%) and SAFR Helmet Cover (PLA: 12.2%; PRA: 9.1%; Risk: 52.2%) produced larger reductions in peak head kinematics and injury risk than the Guardian XT (PLA: 5.7%, PRA: 2.2%, Risk: 21.8%).

CONCLUSION

In laboratory-based assessments that simulated varsity-level impact conditions, the Guardian NXT was associated with larger reductions in PLA, PRA, and injury risk compared to the SAFR Helmet Cover and Guardian XT. Although shell add-ons can enhance head protection, helmet model selection should be prioritized.

Dynamic Soft Tissue Artifacts during Impulsive Loads: Measurement Errors Vary With Wearable Inertial Measurement Unit Sensor Design

OBJECTIVE

Characterize and model Inertial Measurement Unit (IMU) errors due to transient dynamic soft tissue artifacts excited by impulsive loads, such as foot strikes during running and jumping.

METHODS

We instrumented 10 participants (5 female, 5 male) with IMUs on the dominant leg. An ankle IMU measured reference vertical accelerations during impulsive loads and was cross-validated against vertical force measures. Two IMUs on the posterior shank and anterior shank were used to characterize errors caused by dynamic soft tissue artifacts with respect to the reference. Shank sensors' masses were varied to explore their effect on dynamic soft tissue artifacts.

RESULTS

Both the posterior IMU and anterior IMU overestimated peak vertical accelerations during the impulsive load (gain of 2.18 ± 0.63 and 1.55 ± 0.35 respectively). The post- impulsive load oscillation duration and natural frequency varied with sensor mass according to an underdamped second-order system, with posterior IMU and anterior IMU durations of 326 ± 75 ms and 151 ± 50 ms respectively and natural frequencies of 9.79 ± 2.68 Hz and 18.22 ± 12.10 Hz respectively. Low-pass filtering reduced overestimation of peak vertical accelerations, but also attenuated the reference measure.

CONCLUSION

Our study suggests dynamic soft tissue artifacts result in transient, but substantial measurement errors that may not be appropriately mitigated through low-pass filtering. However, these dynamic soft tissue artifacts can be modeled using an underdamped second-order system and used to estimate material properties of underlying soft tissue.

SIGNIFICANCE

We demonstrate that dynamic soft tissue artifacts can be modeled and potentially mitigated to improve accuracy in applications necessitating measurement of impulsive loads such as foot strikes.

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 Head Acceleration Exposure Measurements Using Instrumented Mouthguards: Multi-stage Screening to Optimize Data Quality

Instrumented mouthguards (iMGs) are widely applied to measure head acceleration event (HAE) exposure in sports. Despite laboratory validation, on-field factors including potential sensor skull-decoupling and spurious recordings limit data accuracy. Video analysis can provide complementary information to verify sensor data but lacks quantitative kinematics reference information and suffers from subjectivity. The purpose of this study was to develop a rigorous multi-stage screening procedure, combining iMG and video as independent measurements, aimed at improving the quality of on-field HAE exposure measurements. We deployed iMGs and gathered video recordings in a complete university men's ice hockey varsity season. We developed a four-stage process that involves independent video and sensor data collection (Stage I), general screening (Stage II), cross verification (Stage III), and coupling verification (Stage IV). Stage I yielded 24,596 iMG acceleration events (AEs) and 17,098 potential video HAEs from all games. Approximately 2.5% of iMG AEs were categorized as cross-verified and coupled iMG HAEs after Stage IV, and less than 1/5 of confirmed or probable video HAEs were cross-verified with iMG data during stage III. From Stage I to IV, we observed lower peak kinematics (median peak linear acceleration from 36.0 to 10.9 g; median peak angular acceleration from 3922 to 942 rad/s2) and reduced high-frequency signals, indicative of potential reduction in kinematic noise. Our study proposes a rigorous process for on-field data screening and provides quantitative evidence of data quality improvements using this process. Ensuring data quality is critical in further investigation of potential brain injury risk using HAE exposure data.

Human Head and Helmet Interface Friction Coefficients with Biological Sex and Hair Property Comparisons

Dummy headforms used for impact testing have changed little over the years, and frictional characteristics are thought not to represent the human head accurately. The frictional interface between the helmet and head is an essential factor affecting impact response. However, few studies have evaluated the coefficient of friction (COF) between the human head and helmet surface. This study's objectives were to quantify the human head's static and dynamic COF and evaluate the effect of biological sex and hair properties. Seventy-four participants slid their heads along a piece of helmet foam backed by a fixed load cell at varying normal force levels. As normal force increased, static and dynamic human head COF decreased following power-law curves. At 80 N, the static COF is 0.32 (95% CI 0.30-0.34), and the dynamic friction coefficient is 0.27 (95% CI 0.26-0.28). Biological sex and hair properties were determined not to affect human head COF. The COFs between the head and helmet surface should be used to develop more biofidelic head impact testing methods, define boundary conditions for computer simulations, and aid decision-making for helmet designs.

A comparison of sub-concussive impact attenuating capabilities of ice hockey helmets with and without XRD foam

OBJECTIVES

To compare the impact attenuating capabilities between ice hockey helmets manufactured with and without XRD impact protection foam, worn with and without a XRD skullcap, at reducing sub-concussive head accelerations.

DESIGN

Quasi-experimental laboratory.

METHODS

Ice hockey helmets were fit onto a Hybrid III 50th Head Form Head and dropped 25 times onto the left temporal side for each condition: XRD foam helmet, XRD foam helmet with XRD skullcap adjunct, non-XRD foam helmet, and non-XRD foam helmet with XRD skullcap adjunct. The helmets were dropped from a height that resulted in sub-concussive linear accelerations (25-80 g's). Using a tri-axial accelerometer, peak linear accelerations (g) were measured, and the average was used to compare impact attenuation properties across the four conditions.

RESULTS

The highest linear accelerations were observed in the XRD foam helmet without skullcap (32.97 ± 0.61 g) and were significantly greater (p < 0.001) than the XRD helmet with skullcap (21.38 ± 0.76 g). The helmet without XRD foam elicited the lowest peak linear accelerations (16.10 ± 0.73 g) which were significantly lower than the XRD foam helmet regardless of whether the skullcap was added (p < 0.001).

CONCLUSIONS

Although sub-concussive loads are potentially just as dangerous, much of the research regarding helmet and skullcap efficacy appears to be at high concussive impacts; <70 g's. The findings suggest that helmets with incorporated XRD foam, either within the design or added as an adjunct, are less effective at attenuating linear accelerations at sub-concussive levels than the low-density foam helmet.

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.

Padded Helmet Shell Covers in American Football: A Comprehensive Laboratory Evaluation with Preliminary On-Field Findings

Protective headgear effects measured in the laboratory may not always translate to the field. In this study, we evaluated the impact attenuation capabilities of a commercially available padded helmet shell cover in the laboratory and on the field. In the laboratory, we evaluated the padded helmet shell cover's efficacy in attenuating impact magnitude across six impact locations and three impact velocities when equipped to three different helmet models. In a preliminary on-field investigation, we used instrumented mouthguards to monitor head impact magnitude in collegiate linebackers during practice sessions while not wearing the padded helmet shell covers (i.e., bare helmets) for one season and whilst wearing the padded helmet shell covers for another season. The addition of the padded helmet shell cover was effective in attenuating the magnitude of angular head accelerations and two brain injury risk metrics (DAMAGE, HARM) across most laboratory impact conditions, but did not significantly attenuate linear head accelerations for all helmets. Overall, HARM values were reduced in laboratory impact tests by an average of 25% at 3.5 m/s (range: 9.7 to 39.6%), 18% at 5.5 m/s (range: - 5.5 to 40.5%), and 10% at 7.4 m/s (range: - 6.0 to 31.0%). However, on the field, no significant differences in any measure of head impact magnitude were observed between the bare helmet impacts and padded helmet impacts. Further laboratory tests were conducted to evaluate the ability of the padded helmet shell cover to maintain its performance after exposure to repeated, successive impacts and across a range of temperatures. This research provides a detailed assessment of padded helmet shell covers and supports the continuation of in vivo helmet research to validate laboratory testing results.

The Influence of Headform Friction and Inertial Properties on Oblique Impact Helmet Testing

Helmet-testing headforms replicate the human head impact response, allowing the assessment of helmet protection and injury risk. However, the industry uses three different headforms with varying inertial and friction properties making study comparisons difficult because these headforms have different inertial and friction properties that may affect their impact response. This study aimed to quantify the influence of headform coefficient of friction (COF) and inertial properties on oblique impact response. The static COF of each headform condition (EN960, Hybrid III, NOCSAE, Hybrid III with a skull cap, NOCSAE with a skull cap) was measured against the helmet lining material used in a KASK prototype helmet. Each headform condition was tested with the same helmet model at two speeds (4.8 & 7.3 m/s) and two primary orientations (y-axis and x-axis rotation) with 5 repetitions, totaling 100 tests. The influence of impact location, inertial properties, and friction on linear and rotational impact kinematics was investigated using a MANOVA, and type II sums of squares were used to determine how much variance in dependent variables friction and inertia accounted for. Our results show significant differences in impact response between headforms, with rotational head kinematics being more sensitive to differences in inertial rather than frictional properties. However, at high-speed impacts, linear head kinematics are more affected by changes in frictional properties rather than inertial properties. Helmet testing protocols should consider differences between headforms' inertial and frictional properties during interpretation. These results provide a framework for cross-comparative analysis between studies that use different headforms and headform modifiers.

AI-Based Denoising of Head Impact Kinematics Measurements With Convolutional Neural Network for Traumatic Brain Injury Prediction

OBJECTIVE

Wearable devices are developed to measure head impact kinematics but are intrinsically noisy because of the imperfect interface with human bodies. This study aimed to improve the head impact kinematics measurements obtained from instrumented mouthguards using deep learning to enhance traumatic brain injury (TBI) risk monitoring.

METHODS

We developed one-dimensional convolutional neural network (1D-CNN) models to denoise mouthguard kinematics measurements for tri-axial linear acceleration and tri-axial angular velocity from 163 laboratory dummy head impacts. The performance of the denoising models was evaluated on three levels: kinematics, brain injury criteria, and tissue-level strain and strain rate. Additionally, we performed a blind test on an on-field dataset of 118 college football impacts and a test on 413 post-mortem human subject (PMHS) impacts.

RESULTS

On the dummy head impacts, the denoised kinematics showed better correlation with reference kinematics, with relative reductions of 36% for pointwise root mean squared error and 56% for peak absolute error. Absolute errors in six brain injury criteria were reduced by a mean of 82%. For maximum principal strain and maximum principal strain rate, the mean error reduction was 35% and 69%, respectively. On the PMHS impacts, similar denoising effects were observed and the peak kinematics after denoising were more accurate (relative error reduction for 10% noisiest impacts was 75.6%).

CONCLUSION

The 1D-CNN denoising models effectively reduced errors in mouthguard-derived kinematics measurements on dummy and PMHS impacts.

SIGNIFICANCE

This study provides a novel approach for denoising head kinematics measurements in dummy and PMHS impacts, which can be further validated on more real-human kinematics data before real-world applications.

Cognitive and Salience Network Connectivity Changes following a Single Season of Repetitive Head Impact Exposure in High School Football

BACKGROUND AND PURPOSE

During a season of high school football, adolescents with actively developing brains experience a considerable number of head impacts. Our aim was to determine whether repetitive head impacts in the absence of a clinically diagnosed concussion during a season of high school football produce changes in cognitive performance or functional connectivity of the salience network and its central hub, the dorsal anterior cingulate cortex.

MATERIALS AND METHODS

Football players were instrumented with the Head Impact Telemetry System during all practices and games, and the helmet sensor data were used to compute a risk-weighted exposure metric (RWEcp), accounting for the cumulative risk during the season. Participants underwent MRI and a cognitive battery (ImPACT) before and shortly after the football season. A control group of noncontact/limited-contact-sport athletes was formed from 2 cohorts: one from the same school and protocol and another from a separate, nearly identical study.

RESULTS

Sixty-three football players and 34 control athletes were included in the cognitive performance analysis. Preseason, the control group scored significantly higher on the ImPACT Visual Motor (P = .04) and Reaction Time composites (P = .006). These differences increased postseason (P = .003, P < .001, respectively). Additionally, the control group had significantly higher postseason scores on the Visual Memory composite (P = .001). Compared with controls, football players showed significantly less improvement in the Verbal (P = .04) and Visual Memory composites (P = .01). A significantly greater percentage of contact athletes had lower-than-expected scores on the Verbal Memory (27% versus 6%), Visual Motor (21% versus 3%), and Reaction Time composites (24% versus 6%). Among football players, a higher RWEcp was significantly associated with greater increments in ImPACT Reaction Time (P = .03) and Total Symptom Scores postseason (P = .006). Fifty-seven football players and 13 control athletes were included in the imaging analyses. Postseason, football players showed significant decreases in interhemispheric connectivity of the dorsal anterior cingulate cortex (P = .026) and within-network connectivity of the salience network (P = .018). These decreases in dorsal anterior cingulate cortex interhemispheric connectivity and within-network connectivity of the salience network were significantly correlated with deteriorating ImPACT Total Symptom (P = .03) and Verbal Memory scores (P = .04).

CONCLUSIONS

Head impact exposure during a single season of high school football is negatively associated with cognitive performance and brain network connectivity. Future studies should further characterize these short-term effects and examine their relationship with long-term sequelae.

The Impact of Drop Test Conditions on Brain Strain Location and Severity: A Novel Approach Using a Deep Learning Model

In contact sports such as rugby, players are at risk of sustaining traumatic brain injuries (TBI) due to high-intensity head impacts that generate high linear and rotational accelerations of the head. Previous studies have established a clear link between high-intensity head impacts and brain strains that result in concussions. This study presents a novel approach to investigating the effect of a range of laboratory controlled drop test parameters on regional peak and mean maximum principal strain (MPS) predictions within the brain using a trained convolutional neural network (CNN). The CNN is publicly available at https://github.com/Jilab-biomechanics/CNN-brain-strains . The results of this study corroborate previous findings that impacts to the side of the head result in significantly higher regional MPS than forehead impacts. Forehead impacts tend to result in the lowest region-averaged MPS values for impacts where the surface angle was at 0° and 45°, while side impacts tend to result in higher regional peak and mean MPS. The absence of a neck in drop tests resulted in lower regional peak and mean MPS values. The results indicated that the relationship between drop test parameters and resulting regional peak and mean MPS predictions is complex. The study's findings offer valuable insights into how deep learning models can be used to provide more detailed insights into how drop test conditions impact regional MPS. The novel approach used in this paper to predict brain strains can be applied in the development of better methods to reduce the brain strain resulting from head accelerations such as protective sports headgear.

When to Pull the Trigger: Conceptual Considerations for Approximating Head Acceleration Events Using Instrumented Mouthguards

Head acceleration events (HAEs) are acceleration responses of the head following external short-duration collisions. The potential risk of brain injury from a single high-magnitude HAE or repeated occurrences makes them a significant concern in sport. Instrumented mouthguards (iMGs) can approximate HAEs. The distinction between sensor acceleration events, the iMG datum for approximating HAEs and HAEs themselves, which have been defined as the in vivo event, is made to highlight limitations of approximating HAEs using iMGs. This article explores the technical limitations of iMGs that constrain the approximation of HAEs and discusses important conceptual considerations for stakeholders interpreting iMG data. The approximation of HAEs by sensor acceleration events is constrained by false positives and false negatives. False positives occur when a sensor acceleration event is recorded despite no (in vivo) HAE occurring, while false negatives occur when a sensor acceleration event is not recorded after an (in vivo) HAE has occurred. Various mechanisms contribute to false positives and false negatives. Video verification and post-processing algorithms offer effective means for eradicating most false positives, but mitigation for false negatives is less comprehensive. Consequently, current iMG research is likely to underestimate HAE exposures, especially at lower magnitudes. Future research should aim to mitigate false negatives, while current iMG datasets should be interpreted with consideration for false negatives when inferring athlete HAE exposure.

Blood-Brain Barrier Dysfunction and Exposure to Head Impacts in University Football Players

OBJECTIVE

To investigate the link between dysfunction of the blood-brain barrier (BBB) and exposure to head impacts in concussed football athletes.

DESIGN

This was a prospective, observational pilot study.

SETTING

Canadian university football.

PARTICIPANTS

The study population consisted of 60 university football players, aged 18 to 25. Athletes who sustained a clinically diagnosed concussion over the course of a single football season were invited to undergo an assessment of BBB leakage.

INDEPENDENT VARIABLES

Head impacts detected using impact-sensing helmets were the measured variables.

MAIN OUTCOME MEASURES

Clinical diagnosis of concussion and BBB leakage assessed using dynamic contrast-enhanced MRI (DCE-MRI) within 1 week of concussion were the outcome measures.

RESULTS

Eight athletes were diagnosed with a concussion throughout the season. These athletes sustained a significantly higher number of head impacts than nonconcussed athletes. Athletes playing in the defensive back position were significantly more likely to sustain a concussion than remain concussion free. Five of the concussed athletes underwent an assessment of BBB leakage. Logistic regression analysis indicated that region-specific BBB leakage in these 5 athletes was best predicted by impacts sustained in all games and practices leading up to the concussion-as opposed to the last preconcussion impact or the impacts sustained during the game when concussion occurred.

CONCLUSIONS

These preliminary findings raise the potential for the hypothesis that repeated exposure to head impacts may contribute to the development of BBB pathology. Further research is needed to validate this hypothesis and to test whether BBB pathology plays a role in the sequela of repeated head trauma.

Driver head kinematics in grassroots dirt track racing crashes: A pilot analysis

Motorsport athletes experience head acceleration loading during crashes; however, there is limited literature quantifying the frequency and magnitude of these loads, particularly at the grassroots level of the sport. Understanding head motion experienced during crash events in motorsport is necessary to inform interventions to improve driver safety. This study aimed to quantify and characterize driver head and vehicle kinematics during crashes in open-wheel grassroots dirt track racing. Seven drivers (ages 16-22, n = 2 female) competing in a national midget car series were enrolled in this study over two racing seasons and were instrumented with custom mouthpiece sensors. Drivers' vehicles were outfitted with an incident data recorder (IDR) to measure vehicle acceleration. Forty-one crash events were verified and segmented into 139 individual contact scenarios via film review. Peak resultant linear acceleration (PLA) of the vehicle and PLA, peak rotational acceleration (PRA), and peak rotational velocity (PRV) of the head were quantified and compared across the part of the vehicle contacted (i.e., tires or chassis), the vehicle location contacted (e.g., front, left, bottom), the external object contacted (i.e., another vehicle, wall, or the track), and the principal direction of force (PDOF). The median (95th percentile) PLA, PRA, and PRV of the head and PLA of the vehicle were 12.3 (37.3) g, 626 (1799) rad/s2, 8.92 (18.6) rad/s, and 23.2 (88.1) g, respectively. Contacts with a non-horizontal PDOF (n = 98, 71%) and contact with the track (n = 96, 70%) were common in the data set. Contact to the left side of the vehicle, with the track, and with a non-horizontal PDOF tended to have the greatest head kinematics compared to other factors in each sub-analysis. Results from this pilot study can inform larger studies of head acceleration exposure during crashes in the grassroots motorsports environment and may ultimately support evidence-based driver safety interventions.

Machine-learning-based head impact subtyping based on the spectral densities of the measurable head kinematics

BACKGROUND

Traumatic brain injury can be caused by head impacts, but many brain injury risk estimation models are not equally accurate across the variety of impacts that patients may undergo, and the characteristics of different types of impacts are not well studied. We investigated the spectral characteristics of different head impact types with kinematics classification.

METHODS

Data were analyzed from 3262 head impacts from lab reconstruction, American football, mixed martial arts, and publicly available car crash data. A random forest classifier with spectral densities of linear acceleration and angular velocity was built to classify head impact types (e.g., football, car crash, mixed martial arts). To test the classifier robustness, another 271 lab-reconstructed impacts were obtained from 5 other instrumented mouthguards. Finally, with the classifier, type-specific, nearest-neighbor regression models were built for brain strain.

RESULTS

The classifier reached a median accuracy of 96% over 1000 random partitions of training and test sets. The most important features in the classification included both low- and high-frequency features, both linear acceleration features and angular velocity features. Different head impact types had different distributions of spectral densities in low- and high-frequency ranges (e.g., the spectral densities of mixed martial arts impacts were higher in the high-frequency range than in the low-frequency range). The type-specific regression showed a generally higher R2 value than baseline models without classification.

CONCLUSION

The machine-learning-based classifier enables a better understanding of the impact kinematics spectral density in different sports, and it can be applied to evaluate the quality of impact-simulation systems and on-field data augmentation.

Spinal Cord Boundary Conditions Affect Brain Tissue Strains in Impact Simulations

Brain and spinal cord injuries have devastating consequences on quality of life but are challenging to assess experimentally due to the traumatic nature of such injuries. Finite element human body models (HBM) have been developed to investigate injury but are limited by a lack of biofidelic spinal cord implementation. In many HBM, brain models terminate with a fixed boundary condition at the brain stem. The goals of this study were to implement a comprehensive representation of the spinal cord into a contemporary head and neck HBM, and quantify the effect of the spinal cord on brain deformation during simulated impacts. Spinal cord tissue geometries were developed, based on 3D medical imaging and literature data, meshed, and implemented into the GHBMC 50th percentile male model. The model was evaluated in frontal, lateral, rear, and oblique impact conditions, and the resulting maximum principal strains in the brain tissue were compared, with and without the spinal cord. A new cumulative strain curve metric was proposed to quantify brain strain distribution. Presence of the spinal cord increased brain tissue strains in all simulated cases, owing to a more compliant boundary condition, highlighting the importance of the spinal cord to assess brain response during impact.

Soft-shell headgear in rugby union: a systematic review of published studies

Objectives

To review the rate of soft-shell headgear use in rugby union, consumer knowledge of the protection potential of soft-shell headgear, incidence of concussion reported in rugby headgear studies, and the capacity of soft-shell headgear to reduce acceleration impact forces.

Design

A systematic search was conducted in July and August 2021 using the databases SPORT Discus, PubMed, MEDLINE, CINAHL (EBSCO), Scopus, and Science Direct. The review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The protocol for this systematic review was registered on PROSPERO (registration number: CRD42021239595).

Outcome measures

Rates of headgear use, reports of estimated protection of headgear against head injury, incidence of concussion and magnitude of impact collisions with vs. without headgear, impact attenuation of headgear in lab studies.

Results

Eighteen studies were identified as eligible: qualitative (N = 4), field (N = 7), and lab (N = 7). Qualitative studies showed low rates of headgear use and varying understanding of the protection afforded by headgear. Field studies showed negligible association of headgear use with reduced impact magnitude in headgear vs. non-headgear cohorts. Lab studies showed increased energy attenuation for thicker headgear material, poorer performance of headgear after repetitive impacts and increased drop heights, and promising recent results with headgear composed of viscoelastic polymers.

Conclusions

Rates of adoption of soft-shell headgear remain low in rugby and any association between its use and reduction in acceleration impact forces remains unclear. Lab results indicating improved impact attenuation need to be validated in the field. Further headgear-related research is needed with youth and female rugby players.

Decreased homotopic functional connectivity in traumatic brain injury

INTRODUCTION

Homotopic functional connectivity (HoFC), the synchrony in activity patterns between homologous brain regions, is a fundamental characteristic of resting-state functional connectivity (RsFC).

METHODS

We examined the difference in HoFC, computed as the correlation between atlas-based regions and their counterpart on the opposite hemisphere, in 16 moderate-severe traumatic brain injury patients (msTBI) and 36 healthy controls. Regions of decreased HoFC in msTBI patients were further used as seeds for examining differences between groups in correlations with other brain regions. Finally, we computed logistic regression models of regional HoFC and fractional anisotropy (FA) of the corpus callosum (CC).

RESULTS

TBI patients exhibited decreased HoFC in the middle and posterior cingulate cortex, thalamus, superior temporal pole, and cerebellum III. Furthermore, decreased RsFC was found between left cerebellum III and right parahippocampal cortex and vermis, between superior temporal pole and left caudate and medial left and right frontal orbital gyri. Thalamic HoFC and FA of the CC discriminate patients as msTBI with a high accuracy of 96%.

CONCLUSION

TBI is associated with regionally decreased HoFC. Moreover, a multimodality model of interhemispheric connectivity allowed for a high degree of accuracy in disease discrimination and enabled a deeper understanding of TBI effects on brain interhemispheric reorganization post-TBI.

The Effects of Preparedness and Activity on Head Impacts in Lacrosse Athletes

Considering the frequency and magnitude of head impacts occurring during sport participation is important to guide prevention initiatives. Our purpose was to compare magnitude and frequency of lacrosse players’ head impacts based on anticipation level and impact activity. Lacrosse athletes (16 men, 15 women) wore xPatch sensors during games and practices that measured impact magnitude (linear and rotational accelerations) and frequency of video verified head impacts. The interaction between impact activity and preparedness was not significant, multivariate: F(8, 1,730) = ;1.03, p = ;.41, η2 = ;.01. Having a detailed understanding of the characteristics of head impacts could allow for focused interventions to reduce injury risk.

A Fiber-Optic Sensor-Embedded and Machine Learning Assisted Smart Helmet for Multi-Variable Blunt Force Impact Sensing in Real Time

Early on-site diagnosis of mild traumatic brain injury (mTBI) will provide the best guidance for clinical practice. However, existing methods and sensors cannot provide sufficiently detailed physical information related to the blunt force impact. In the present work, a smart helmet with a single embedded fiber Bragg grating (FBG) sensor is developed, which can monitor complex blunt force impact events in real time under both wired and wireless modes. The transient oscillatory signal "fingerprint" can specifically reflect the impact-caused physical deformation of the local helmet structure. By combination with machine learning algorithms, the unknown transient impact can be recognized quickly and accurately in terms of impact magnitude, direction, and latitude. Optimization of the training dataset was also validated, and the boosted ML models, such as the S-SVM+ and S-IBK+, are able to predict accurately with complex databases. Thus, the ML-FBG smart helmet system developed by this work may become a crucial intervention alternative during a traumatic brain injury event.

Simulated Astronaut Kinematics and Injury Risk for Piloted Lunar Landings and Launches While Standing

During future lunar missions, astronauts may be required to pilot vehicles while standing, and the associated kinematic and injury response is not well understood. In this study, we used human body modeling to predict unsuited astronaut kinematics and injury risk for piloted lunar launches and landings in the standing posture. Three pulses (2-5 g; 10-150 ms rise times) were applied in 10 directions (vertical; ± 10-degree offsets) for a total of 30 simulations. Across all simulations, motion envelopes were computed to quantify displacement of the astronaut's head (max 9.0 cm forward, 7.0 cm backward, 2.1 cm upward, 7.3 cm downward, 2.4 cm lateral) and arms (max 25 cm forward, 35 cm backward, 15 cm upward, 20 cm downward, 20 cm lateral). All head, neck, lumbar, and lower extremity injury metrics were within NASA's tolerance limits, except tibia compression forces (0-1543 N upper tibia; 0-1482 N lower tibia; tolerance-1350 N) and revised tibia index (0.04-0.58 upper tibia; 0.03-0.48 lower tibia; tolerance-0.43) for the 2.7 g/150 ms pulse. Pulse magnitude and duration contributed over 80% to the injury metric values, whereas loading direction contributed less than 3%. Overall, these simulations suggest piloting a lunar lander vehicle in the standing posture presents a tibia injury risk which is potentially outside NASA's acceptance limits and warrants further investigation.

A Review of Head Injury Metrics Used in Automotive Safety and Sports Protective Equipment

Despite advances in the understanding of human tolerances to brain injury, injury metrics used in automotive safety and protective equipment standards have changed little since they were first implemented nearly a half-century ago. Although numerous metrics have been proposed as improvements over the ones currently used, evaluating the predictive capability of these metrics is challenging. The purpose of this review is to summarize existing head injury metrics that have been proposed for both severe head injuries, such as skull fractures and traumatic brain injuries (TBI), and mild traumatic brain injuries (mTBI) including concussions. Metrics have been developed based on head kinematics or intracranial parameters such as brain tissue stress and strain. Kinematic metrics are either based on translational motion, rotational motion, or a combination of the two. Tissue-based metrics are based on finite element model simulations or in vitro experiments. This review concludes with a discussion of the limitations of current metrics and how improvements can be made in the future.

[Traumatic brain injuries in winter sports : An overview based on the winter sports skiing, snowboarding and ice hockey]

In winter sports, skiers, snowboarders and ice hockey players have the highest risk of traumatic brain injuries (TBI). In skiing/snowboarding severe TBIs are of concern; in ice hockey, repetitive minor TBIs are frequent. The main causes of TBI in recreational skiing are collisions with trees; in professionals falls due to technical or tactical mistakes are the main causes. In ice hockey 10-15% of all injuries are due to a sports-related concussion (SRC), mostly caused by player-opponent contact. The pathomechanism in TBI is a combination of rotational and linear acceleration during head impact, which causes a diffuse axonal injury. Long-term complications such as neurodegenerative diseases and functional deficits are of relevance. Prevention by wearing helmets is effective, but less effective in TBI/SRC than in focal injuries.

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.

Exploring the Effects of a Neck Strengthening Program on Purposeful Soccer Heading Biomechanics and Neurocognition

Background

Cervical (neck) strengthening has been proposed as an important factor in concussion prevention. The purpose of the study was to determine if a six-week cervical strengthening program affected neurocognition and purposeful soccer heading biomechanics. The hypothesis was that the neck strengthening program would improve strength, maintain neurocognition, and alter purposeful soccer heading biomechanics.

Study Design

Randomized controlled trial.

Methods

Twenty collegiate soccer athletes (8 males, 12 females, age=20.15±1.35 years, height=171.67±9.01 cm, mass=70.56±11.03 kg) volunteered to participate. Time (pre, post) and group (experimental, control) served as the independent variables. Four composite scores from the CNS Vital Signs computer based neurocognitive test (CNSVS; verbal memory, visual memory, executive function, reaction time) and aspects of heading biomechanics from inertial measurement units (xPatch; peak linear acceleration, peak rotational acceleration, duration, Gadd Severity Index [GSI]) served as the dependent variables. Each athlete completed a baseline measure of neck strength (anterior neck flexors, bilateral anterolateral neck flexors, bilateral cervical rotators) and CNSVS after heading 10 soccer balls at two speeds (11.18 and 17.88 m/s) while wearing the xPatch. The experimental group completed specific cervical neck strengthening exercises twice a week for six weeks using a Shingo Imara™ cervical neck resistance apparatus while the control group did not. After six weeks, the participants completed the same heading protocol followed by measurement of the same outcome variables. The alpha value was set to p<0.05 a priori.

Results

The interaction between time and group was significant for visual memory (F1,17=5.16, p=0.04, η2=0.23). Interestingly, post hoc results revealed visual memory decreased for the control group from pretest (46.90±4.46) compared to posttest (43.00±4.03; mean difference=3.90, 95% CI=0.77-7.03, p=0.02). Interactions for all other dependent variables were not statistically significant (p>0.05).

Conclusions

The cervical neck strengthening protocol allowed maintenance of visual memory scores but did not alter other neurocognitive measures or heading biomechanics. The link between cervical neck strengthening and concussion predisposition should continue to be explored.

Level of Evidence

Level 1b.

Consensus Head Acceleration Measurement Practices (CHAMP): Laboratory Validation of Wearable Head Kinematic Devices

Wearable devices are increasingly used to measure real-world head impacts and study brain injury mechanisms. These devices must undergo validation testing to ensure they provide reliable and accurate information for head impact sensing, and controlled laboratory testing should be the first step of validation. Past validation studies have applied varying methodologies, and some devices have been deployed for on-field use without validation. This paper presents best practices recommendations for validating wearable head kinematic devices in the laboratory, with the goal of standardizing validation test methods and data reporting. Key considerations, recommended approaches, and specific considerations were developed for four main aspects of laboratory validation, including surrogate selection, test conditions, data collection, and data analysis. Recommendations were generated by a group with expertise in head kinematic sensing and laboratory validation methods and reviewed by a larger group to achieve consensus on best practices. We recommend that these best practices are followed by manufacturers, users, and reviewers to conduct and/or review laboratory validation of wearable devices, which is a minimum initial step prior to on-field validation and deployment. We anticipate that the best practices recommendations will lead to more rigorous validation of wearable head kinematic devices and higher accuracy in head impact data, which can subsequently advance brain injury research and management.

Drop Test Kinematics Using Varied Impact Surfaces and Head/Neck Configurations for Rugby Headgear Testing

World Rugby employs a specific drop test method to evaluate headgear performance, but almost all researchers use a different variation of this method. The aim of this study was, therefore, to quantify the differences between variations of the drop testing method using a Hybrid III headform and neck in the following impact setups: (1) headform only, with a flat steel impact surface, approximating the World Rugby method, (2 and 3) headform with and without a neck, respectively, onto a flat MEP pad impact surface, and (4) headform and neck, dropped onto an angled MEP pad impact surface. Each variation was subject to drop heights of 75-600 mm across three orientations (forehead, side, and rear boss). Comparisons were limited to the linear and rotational acceleration and rotational velocity for simplicity. Substantial differences in kinematic profile shape manifested between all drop test variations. Peak accelerations varied highly between variations, but the peak rotational velocities did not. Drop test variation also significantly changed the ratios of the peak kinematics to each other. This information can be compared to kinematic data from field head impacts and could inform more realistic impact testing methods for assessing headgear.

Mechanisms of Sports Concussion in Taekwondo: A Systematic Video Analysis of Seven Cases

Sports-related traumatic brain injuries are the most common injury in adolescents and young adults due to recurrent concussion experiences and head shock. Therefore, this study was designed to describe player characteristics and situational factors associated with concussions in the World Taekwondo Championships using systematic video analysis. Athlete injury data were collected using a web-based injury surveillance system at the World Taekwondo Championships organized by World Taekwondo from 2017 to 2019. Seven video footage were independently analyzed by four analysts using a modified Heads-Up Checklist. Descriptive statistical analysis was used. The incidence of concussion was 3.21 per 1000 games. Most players with concussions were shorter than their opponents, and most concussions were caused by a roundhouse kick on the front of the face. Regarding the acceleration direction of the head after the impact, transverse and multiplane directions were the most common. Most players with a concussion have used a closed stance and did not use blocking techniques during the defense. The rate of concussions caused by penalties was 42.9%. Based on our findings, no other injury mechanisms, except for direct blows to the head, were observed. Therefore, education on the risk and symptoms of concussion, the appropriate management and blocking techniques should be emphasized in TKD-S to reduce incidence of concussion.

Time Delta Head Impact Frequency: An Analysis on Head Impact Exposure in the Lead Up to a Concussion: Findings from the NCAA-DOD Care Consortium

Sport-related concussions can result from a single high magnitude impact that generates concussive symptoms, repeated subconcussive head impacts aggregating to generate concussive symptoms, or a combined effect from the two mechanisms. The array of symptoms produced by these mechanisms may be clinically interpreted as a sport-related concussion. It was hypothesized that head impact exposure resulting in concussion is influenced by severity, total number, and frequency of subconcussive head impacts. The influence of total number and magnitude of impacts was previously explored, but frequency was investigated to a lesser degree. In this analysis, head impact frequency was investigated over a new metric called ‘time delta’, the time difference from the first recorded head impact of the day until the concussive impact. Four exposure metrics were analyzed over the time delta to determine whether frequency of head impact exposure was greater for athletes on their concussion date relative to other dates of contact participation. Those metrics included head impact frequency, head impact accrual rate, risk weighted exposure (RWE), and RWE accrual rate. Athletes experienced an elevated median number of impacts, RWE, and RWE accrual rate over the time delta on their concussion date compared to non-injury sessions. This finding suggests elevated frequency of head impact exposure on the concussion date compared to other dates that may precipitate the onset of concussion.