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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.

Design of helmets used in contact sports has been driven by the necessity of preventing severe head injuries. Manufacturing standards and pass or fail grading systems ensure protective headgear built to withstand large impacts, but design standards do no account for impacts resulting in subconcussive episodes and the effects of cumulative impacts on its user. Thus, it is important to explore new design parameters, such as the frequency-domain measures of transmissibility and mechanical impedance that are based on energy absorption from a range of impact loads. Within the experimentally determined frequency range of interest (FROI), transmissibilities above unity were found in the 0–40 Hz range with the magnitude characteristics varying considerably with impact location. A similar variability with location was observed for the mechanical impedance, which ranged from 9 N/m to 50 N/m. Additional research is required to further understand how changes in the components or materials of the components will affect the performance of helmets, and how they may be used to reduce both transmissibility and dynamic impedance.

Quantifying head impacts is a vital component to understanding and preventing head trauma in sport. Our objective was to establish the frequency and magnitude of head impact mechanisms in men’s lacrosse athletes. Eleven male lacrosse athletes wore xPatch sensors during activity. Video footage of practices and games was analyzed to verify impacts and code them with impact mechanisms. The authors calculated incidence rates (IRs) per 1000 exposures with corresponding 95% confidence intervals (CIs) and used multivariate analysis of variances to compare the linear (g) and rotational (rad/s2) accelerations between mechanisms. A total of 167 head impacts were successfully verified and coded with a mechanism using video footage during 542 total exposures. The highest IR was head to body (IR = 118.08; 95% CI, 89.15–147.01), and the lowest was head to ball (IR = 3.69; 95% CI, 0–8.80) (incidence rate ratio = 32.00; 95% CI, 67.83–130.73). Analysis indicated that impact mechanism failed to significantly alter the combined dependent variables (multivariate F10,306 = 1.79, P = .06, η2 = .06, 1−β = 0.83). While head to head, body to head, and stick to head mechanisms are penalty-inducing offenses in men’s lacrosse, head to ground, head to ball, and combination impacts have similar head accelerations. If penalties and rules are created to protect players from traumatic head injury, the authors recommend stricter enforcement.

Background Head impacts have been studied extensively in football, but little similar research has been conducted in men's lacrosse. It is important to understand the location and magnitude of head impacts during men's lacrosse to recognize the risk of head injury. Methods Descriptive epidemiology study set on collegiate lacrosse fields. Eleven men's lacrosse players (age=20.9±1.13years, mass=83.91±9.04kg, height=179.88±5.99cm) volunteered to participate. We applied X2 sensors behind the right ear of participants for games and practices. Sensors recorded data on linear and rotational accelerations and the location of head impacts. We calculated incidence rates per 1000 exposures with 95% confidence intervals for impact locations and compared the effect of impact location on linear and rotational accelerations with Kruskal-Wallis tests. Findings We verified 167 head impacts (games=112; practices=55). During games, the incidence rate was 651.16 (95% confidence interval=530.57–771.76). The high and low incidence rates for head impact locations during games were: side=410.7 (95% confidence interval=292.02–529.41) and top=26.79 (95% confidence interval=3.53–57.10). For games and practices combined, the impact locations did not significantly affect linear ( χ 2 3 =6.69, P =0.08) or rotational acceleration ( χ 2 3 =6.34, P =0.10). Interpretation We suggest further research into the location of head impacts during games and practices. We also suggest player and coach education on head impacts as well as behavior modification in men's lacrosse athletes to reduce the incidence of impacts to the side of the head in an effort to reduce potential injury.

Pressure sensitive adhesives (PSAs) are highly viscoelastic rubber-like materials which are widely employed to bond a range of materials. They typically exhibit rubbery-plateau shear moduli on the order of 1 MPa and glass-plateau shear moduli on the order of 1 GPa with variable levels of strain-rate sensitivity within each rheological plateau. PSAs are frequently employed in applications which can result in high rate and large deformation loading; however, characterization frequently emphasizes small-strain viscoelastic properties as measured by dynamic mechanical analysis (DMA) with time-temperature superposition. Kolsky bar (split-Hopkinson pressure bar) testing can provide direct measurement of the high-rate, finite strain properties; however, the experimental challenges to obtain reliable data are well documented for soft materials. Specifically, soft material testing is sensitive to issues with sample stress equilibrium, radial inertia effects, and poor signal to noise ratio. These challenges are compounded in PSAs, which are apt to adhere to the bar surfaces and can chemically interact with typical lubricants, thus changing the properties.

The National Operating Committee on Standards for Athletic Equipment (NOCSAE) has developed impact attenuation thresholds that protective helmets worn in sport must meet to be commercially available in an attempt to prevent injury. It remains unknown how normal helmet use in athletic activity alters the force attenuation ability of lacrosse helmets. We tested 3 new and 3 randomly selected used helmets from 2 popular lacrosse models (Cascade Pro7, Cascade CPXR). All used helmets had been worn for 3 collegiate seasons prior to testing and had never been refurbished. Helmets were drop-tested using 3 prescribed impact velocities at 6 locations according to the NOCSAE lacrosse helmet standard, and we compared the Gadd Severity Index (GSI) scores between new and used helmets using a repeated measure ANOVA with location as the repeated variable and data separated by impact velocity. All 12 helmets passed the NOCSAE GSI threshold for all testing conditions; however 1 used helmet shell cracked resulting in a failed test. We found a significant main effect for helmet age at the low (F5,50=2.98, P=.02), medium (F5,50=3.71, P=.006), and high (F5,50=2.70, P=.03) velocities. We suspect that helmet use can degrade materials under some conditions, but improve performance in others due to changes in helmet composition from use. The clinical implications of the differences in GSI scores noted remain unclear. Because one helmet shell cracked resulting in a failed test, used helmets should be regularly inspected for cracks or other signs of mechanical fatigue that may weaken helmet integrity.

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

Monte-Carlo permutation analysis was used to identify sets of head impacts most predictive of functional magnetic resonance imaging (fMRI) changes in football players. The relative distribution of impact location was found to be more predictive of brain activation changes than the number of impacts, suggesting that fMRI changes are related to systematic playing style.

Magnetic resonance spectroscopy and helmet telemetry were used to monitor the neural metabolic response to repetitive head collisions in 25 high school American football athletes. Specific hit characteristics were determined highly predictive of metabolic alterations, suggesting that sub-concussive blows can produce biochemical changes and potentially lead to neurological problems.

Context: The Guardian Cap provides a soft covering intended to mitigate energy transfer to the head during football contact. Yet how well it attenuates impacts remains unknown. Objective: To evaluate the changes in the Gadd Severity Index (GSI) and linear acceleration during drop tests on helmeted headforms with or without Guardian Caps. Design: Crossover study. Setting: Laboratory. Patients or Other Participants: Nine new football helmets sent directly from the manufacturer. Intervention(s): We dropped the helmets at 3 velocities on 6 helmet locations (front, side, right front boss, top, rear right boss, and rear) as prescribed by the National Operating Committee on Standards for Athletic Equipment. Helmets were tested with facemasks in place but no Guardian Cap and then retested with the facemasks in place and the Guardian Cap affixed. Main Outcome Measure(s): The GSI scores and linear accelerations measured in g forces. Results: For the GSI, we found a significant interaction among drop location, Guardian Cap presence, and helmet brand at the high velocity (F10,50 = 3.01, P = .005) but not at the low (F3.23,16.15 = 0.84, P = .50) or medium (F10,50 = 1.29, P = .26) velocities. Similarly for linear accelerations, we found a significant interaction among drop location, Guardian Cap presence, and helmet brand at the high velocity (F10,50 = 3.01, P = .002, ω2 = 0.05) but not at the low (F10,50 = 0.49, P = .89, ω2 < 0.01, 1–β = 0.16) or medium (F5.20,26.01 = 2.43, P = .06, ω2 < 0.01, 1–β = 0.68) velocities. Conclusions: The Guardian Cap failed to significantly improve the helmets' ability to mitigate impact forces at most locations. Limited evidence indicates how a reduction in GSI would provide clinically relevant benefits beyond reducing the risk of skull fracture or a similar catastrophic event.

Recent work suggests that repetitive subconcussive head impacts may contribute to long-term neurodegeneration; however, the risk thresholds for subconcussive injury are unknown. It was hypothesized that the number and severity of head impacts could quantify the risk of developing abnormal neurophysiology. Twenty-one high school boys (ages 14 to 18) participating in varsity and junior varsity football were evaluated over the course of 1 football season (13 games) using a combination of the ImPACT, functional magnetic resonance imaging (fMRI), and head impact telemetry. The number and severity of head impacts throughout the football season were subsequently compared with the fraction of players flagged by either the ImPACT or fMRI before, during, and after the competition season. Twelve of 22 (54.5%) in-season tests of asymptomatic participants had a minimum of 1 composite ImPACT score flagged. For the fMRI analysis, 16 (72.7%) of the 22 in-sea son sessions were considered flagged. Seven assessments were flagged by both the ImPACT and fMRI. Larger numbers of hits appeared to correspond with a larger fraction of players being flagged by at least fMRI or the ImPACT. A substantial number of clinically asymptomatic athletes exhibit significant neurophysi ological changes in-season. Furthermore, the number of head impacts is a risk factor for the development of neurophysiological changes. [Athletic Training & Sports Health Care. 2014;6(x):xxxxxx.] [Query #2: Reduce to 150 words.]

Head trauma and concussion in football players have recently received considerable media attention. Postmortem evidence suggests that accrual of damage to the brain may occur with repeated blows to the head, even when the individual blows fail to produce clinical symptoms. There is an urgent need for improved detection and characterization of head trauma to reduce future injury risk and promote development of new therapies. In this study we examined neurological performance and health in the presence of head collision events in high school football players, using longitudinal measures of collision events (the HIT(™) System), neurocognitive testing (ImPACT(™)), and functional magnetic resonance imaging MRI (fMRI). Longitudinal assessment (including baseline) was conducted in 11 young men (ages 15-19 years) participating on the varsity and junior varsity football teams at a single high school. We expected and observed subjects in two previously described categories: (1) no clinically-diagnosed concussion and no changes in neurological behavior, and (2) clinically-diagnosed concussion with changes in neurological behavior. Additionally, we observed players in a previously undiscovered third category, who exhibited no clinically-observed symptoms associated with concussion, but who demonstrated measurable neurocognitive (primarily visual working memory) and neurophysiological (altered activation in the dorsolateral prefrontal cortex [DLPFC]) impairments. This new category was associated with significantly higher numbers of head collision events to the top-front of the head, directly above the DLPFC. The discovery of this new category suggests that more players are suffering neurological injury than are currently being detected using traditional concussion-assessment tools. These individuals are unlikely to undergo clinical evaluation, and thus may continue to participate in football-related activities, even when changes in brain physiology (and potential brain damage) are present, which will increase the risk of future neurological injury.

Dynamic mechanical properties are critical in the evaluation of materials with viscoelastic behavior. Various techniques, including dynamic mechanical analysis (DMA), rheology, nanoindentation, and others have been developed for this purpose and typically report complex modulus. Each of these techniques has strengths and weaknesses depending on sample geometry and length scale, mechanical properties, and skill of the user. In many industry applications, techniques may also be blindly applied according to a standard procedure without optimization for a specific sample. This can pose challenges for correct characterization of novel materials, and some techniques are more robust to agnostic application than others. A relative assessment of dynamic mechanical techniques is important when considering the appropriate technique to use to characterize a material. It also has bearing on organizations with limited resources that must strategically select one or two capabilities to meet as broad a set of materials as possible. The purpose of this study was to evaluate the measurement characteristics (e.g., precision and bias) of a selection of six dynamic mechanical test methods on a range of polymeric materials. Such a comprehensive comparison of dynamic mechanical testing methods was not identified in the literature. We also considered other technical characteristics of the techniques that influence their usability and strategic value to a laboratory and introduce a novel use of the House of Quality method to systematically compare measurement techniques. The selected methods spanned a range of length scales, frequency ranges, and prevalence of use. DMA, rheology, and oscillatory loading using a servohydraulic tensile tester were evaluated as traditional bulk techniques. Determination of complex modulus by beam vibration was also considered as a bulk technique. At a small length scale, both an oscillatory nanoindentation method and AFM were evaluated. Each method was employed to evaluate samples of polycarbonate, polypropylene, amorphous PET, and semi-crystalline PET. A measurement systems analysis (MSA) based on the ANOVA methods outlined in ASTM E2782 was conducted using storage modulus data obtained at 1 Hz. Additional correlations over a range of frequencies were tested between rheology/DMA and the remaining methods. Note that no attempts were made to optimize data collection for the test specimens. Rather, typical test methods were applied in order to simulate the type of results that would be expected in typical industrial characterization of materials. Data indicated low levels of repeatability error ( MSA results were subsequently evaluated along with other technical attributes of the instruments using the House of Quality method. Technical attributes were weighted against a set of “user demands” that reflect the qualitative expectations often placed on measurement systems. Based on this analysis, we determined that DMA and rheology provide the broadest capability while remaining robust and easy to use. Other techniques, such as nanoindentation and vibrations, have unique qualities that fulfill niche applications where DMA and rheology are not suitable. This analysis provides an industry-relevant evaluation of measurement techniques and demonstrates a framework for evaluating the capabilities of analytical equipment relative to organizational needs.

Although the National Operating Committee on Standards for Athletic Equipment (NOCSAE) standards are similar for football and lacrosse helmets, it remains unknown how helmets for each sport compare on drop tests. Due to the increased concern over head injury in sport and the rapid growth in lacrosse participation, it is useful to compare the performance of various football and lacrosse helmets. Therefore, the goal of this study was to document the impact attenuation properties of football and lacrosse helmets and to identify the relative performance between helmets for the two sports. Six models of football and six models of lacrosse helmets were tested using a drop tower at three prescribed velocities and six locations on the helmets. A repeated measures ANOVA was conducted to determine the effect of sport on Gadd Severity Index (GSI) scores and linear accelerations. The interaction between location and sport was significant at the low (F2.64,89.71=7.68, P

Longitudinal evaluation using diffusion-weighted imaging and collision event monitoring was performed on high school athletes who participate in American football. Observed changes in white matter health were suggestive of injury and found to be correlated with accumulation of head collision events during practices and games.

Neurocognitive assessment, functional magnetic resonance imaging, and head impact monitoring were used to evaluate neurological changes in high school football players throughout competitive seasons. A substantial number of asymptomatic athletes exhibited neurophysiological changes that persisted post-season, with abnormal measures significantly more common in athletes receiving 50 or more hits per week during the season.

Soccer is the source of the highest concussion rates among female athletes and is associated with neurological deficits at many levels of play. Despite its importance to our understanding of head trauma in female athletes, little is known about the number and magnitude of head impacts experienced by female soccer players. Head impacts experienced by high school and collegiate athletes were quantified using xPatch sensors (X2 Biosystems) affixed behind the right ear of each player. The average peak translational acceleration (PTA) sustained by players at the high school level was significantly lower than that of the collegiate players, but the average peak angular accelerations (PAA) were not significantly different. Given that the collegiate players took many more impacts throughout the season, their mean cumulative exposure to translational (cPTA) and angular accelerations (cPAA) were significantly higher than those of the high school players. Additional research is required to determine whether the differences in cumulative exposure are responsible for the elevated risk of concussion in collegiate soccer players or if there are additional risk factors.

Objective For both subconcussive impacts and traditionally-defined concussion, neither the number of head impacts nor the magnitude has had a strong correlation to the incidence or severity of injury. Recent modelling work has suggested that impulse may be an important biomechanical factor, and therefore it is hypothesised that it may be a good predictor of subconcussive neurophysiological changes. Design Observational study. Setting American high school football team. Participants Nine male high school football athletes (mean age=16.4, range=15–17) volunteered. All participants were enrolled with parental consent. Assessment of risk factors Head impacts were monitored at all practices and games with the Head Impact Telemetry System. Baseline neurophysiology was measured prior to contact activity using a functional magnetic resonance imaging (fMRI) visual n-back task protocol. Subjects returned throughout the season and were re-evaluated according to the same protocol. Outcome measures Kinematic impulse was computed from head impact telemetry. Changes in neurophysiology were determined as the difference in the 2 vs. 1-back contrast. This contrast was determined for 116 anatomically defined regions of interest (ROI). Main results Stepwise regressions (P=0.05) relating kinematic impulse to ROI-specific changes in neurophysiology yielded significant correlations for 57/116 ROIs. 22/116 ROIs had an R2 value greater than 0.70. Correlations were found bilaterally for 16 anatomical ROIs, including the executive pre-frontal regions, basal ganglia, and thalamus. Conclusions The relationship between kinematic impulse and fMRI changes reported here are the strongest correlations to subconcussive changes reported to date. Correlations were observed bilaterally in regions associated with concussion symptoms. Competing interests None.

Long-term neurological damage as a result of head trauma while playing sports is a major concern for football athletes today. Repetitive concussions have been linked to many neurological disorders. Recently, it has been reported that repetitive subconcussive events can be a significant source of accrued damage. Since football athletes can experience hundreds of subconcussive hits during a single season, it is of utmost importance to understand their effect on brain health in the short and long term. In this study, resting-state functional magnetic resonance imaging (rs-fMRI) was used to study changes in the default mode network (DMN) after repetitive subconcussive mild traumatic brain injury. Twenty-two high school American football athletes, clinically asymptomatic, were scanned using the rs-fMRI for a single season. Baseline scans were acquired before the start of the season, and follow-up scans were obtained during and after the season to track the potential changes in the DMN as a result of experienced trauma. Ten noncollision-sport athletes were scanned over two sessions as controls. Overall, football athletes had significantly different functional connectivity measures than controls for most of the year. The presence of this deviation of football athletes from their healthy peers even before the start of the season suggests a neurological change that has accumulated over the years of playing the sport. Football athletes also demonstrate short-term changes relative to their own baseline at the start of the season. Football athletes exhibited hyperconnectivity in the DMN compared to controls for most of the sessions, which indicates that, despite the absence of symptoms typically associated with concussion, the repetitive trauma accrued produced long-term brain changes compared to their healthy peers.

With growing evidence of long-term neurological damage in individuals enduring repetitive head trauma, it is critical to detect lower-level damage accumulation for the early diagnosis of injury in at-risk populations. Proton magnetic resonance spectroscopic scans of the dorsolateral prefrontal cortex and primary motor cortex were collected from high school American (gridiron) football athletes, prior to and during their competition seasons. Although no concussions were diagnosed, significant metabolic deviations from baseline and non-collision sport controls were revealed. Overall the findings indicate underlying biochemical changes, consequential to repetitive hits, which have previously gone unnoticed due to a lack of traditional neurological symptoms.

a Department of Athletic Training, Lynchburg College, Lynchburg, VA 24501, United States b Department of Health and Kinesiology, Purdue University, West Lafayette, IN 47907, United States c School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, United States d Department of Exercise Science and Sport Studies, Springfield College, Springfield, MA 01109, United States e Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, United States f Department of Basic Medical Sciences, Purdue University, West Lafayette, IN 47907, United States

Background Recent work suggests that repetitive sub-concussive head impacts may contribute to long-term neurodegeneration; however, the risk thresholds for sub-concussive injury are unknown. Objective To evaluate the risk of developing abnormal neurophysiology due to repetitive impacts to the head. Hypothesis: the number of head impacts is predictive of neurological impairment. Design ImPACT, fMRI, and head impact telemetry (HIT) was employed in baseline tests, pre-season and in-season. The number and magnitude of head impacts were collected for practices and games. Setting American high school football. Participants 13 high school American football players age 14–18. Those diagnosed with a concussion were excluded. Risk factor assessment The number of head impacts during the season. Main outcome measurements Pre-season and in-season ImPACT, MRI, and fMRI. Results The players experienced an average of 17.7 to 45.5 hits/week with a mean and standard deviation of 71.7±39.3. The corresponding cumulative number of hits for the season ranged from 86 to 1996 with a mean and standard deviation of 582.8±444.3. Twenty-two in-season ImPACT tests were administered during the season. Twelve (54.5%) showed a minimum of one composite score flagged, the fMRI analysis showed 16 (72.7%) in-season assessments flagged, and seven subjects were flagged by both the ImPACT and fMRI. Groups were divided based on number of head impacts; those above & below 500 cumulative hits/season and above and below 65 hits/week. Above 500 cumulative hits/season and 65 hits/week, all examinations were flagged. Conclusions A number of asymptomatic athletes exhibited neurophysiological changes. The number of head impacts is a risk factor for the development of neurophysiological changes. The medical staff should monitor players who are taking large numbers of hits, consider using neurocognitive testing on an annual basis, and promote proper technique and skill development for the players.