Biomechanical correlates of symptomatic and asymptomatic neurophysiological impairment in high school football

A Prospective Transcranial Doppler Ultrasound-Based Evaluation of the Effects of Repetitive Subconcussive Head Trauma on Neurovascular Coupling Dynamics

OBJECTIVE

To determine the effects of repetitive subconcussive head trauma on neurovascular coupling (NVC) responses.

DESIGN

Prospective cohort study collected between September 2013 and December 2016.

SETTING

University laboratory.

PARTICIPANTS

One hundred seventy-nine elite, junior-level (age, 19.6 ± 1.5 years) contact sport (ice hockey, American football) athletes recruited for preseason testing. Fifty-two nonconcussed athletes returned for postseason testing. Fifteen noncontact sport athletes (age, 20.4 ± 2.2 years) also completed preseason and postseason testing.

EXPOSURE(S)

Subconcussive sport-related head trauma.

MAIN OUTCOME MEASURES

Dynamics of NVC were estimated during cycles of 20 seconds eyes closed and 40 seconds eyes open to a visual stimulus (reading) by measuring cerebral blood flow (CBF) velocity in the posterior (PCA) and middle (MCA) cerebral arteries via transcranial Doppler ultrasound.

RESULTS

Both athlete groups demonstrated no significant differences in PCA or MCA NVC dynamics between preseason and postseason, despite exposure to a median of 353.5 (range, 295.0-587.3) head impacts (>2g) over the course of the season for contact sport athletes.

CONCLUSIONS

Within the context of growing concern over detrimental effects of repetitive subconcussive trauma, the current results encouragingly suggest that the dynamics of NVC responses are not affected by 1 season of participation in junior-level ice hockey or American football. This is an important finding because it indicates an appropriate postseason CBF response to elevated metabolic demand with increases in neural activity.

A novel repetitive head impact exposure measurement tool differentiates player position in National Football League

American-style football participation poses a high risk of repetitive head impact (RHI) exposure leading to acute and chronic brain injury. The complex nature of symptom expression, human predisposition, and neurological consequences of RHI limits our understanding of what constitutes as an injurious impact affecting the integrity of brain tissue. Video footage of professional football games was reviewed and documentation made of all head contact. Frequency of impact, tissue strain magnitude, and time interval between impacts was used to quantify RHI exposure, specific to player field position. Differences in exposure characteristics were found between eight different positions; where three unique profiles can be observed. Exposure profiles provide interpretation of the relationship between the traumatic event(s) and how tissue injury is manifested and expressed. This study illustrates and captures an objective measurement of RHI on the field, a critical component in guiding public policy and guidelines for managing exposure.

Effects of Repetitive Head Impacts on a Concussion Assessment Battery

PURPOSE

The purpose of this study was to determine the relationship between repetitive head impacts (RHI) and clinical concussion assessments across a season among collegiate football (FB) and women's soccer (WSOC) players.

METHODS

Fifteen male FB and 23 WSOC players participated in this study. Participants were included if they were medically cleared for unrestricted athletic participation. Participants were tested in a university athletic training room on two occasions: preseason (PRE) and postseason (POST). The outcome measures consisted of tandem gait (TG), Standardized Assessment of Concussion, Balance Error Scoring System, King-Devick (KD), clinical reaction time, and Immediate Post-Concussion Assessment and Cognitive Testing. Repetitive head impact during the season was quantified using the Head Impact Telemetry System (Simbex, NH) for FB and the Smart Impact Monitor (SIM; Triax Technologies, Norwalk, CT) for WSOC. Independent variables included total number of impacts, average magnitude of peak linear acceleration, cumulative linear exposure, and number of impacts ≥98g.

RESULTS

Results from direct-entry multiple regression analyses suggest significant associations between RHI and both visual memory (R = 0.670, F = 6.487, P = 0.002) and TG (R = 0.636, F = 3.841, P = 0.029) for WSOC and between RHI and KD (R = 0.756, F = 5.579, P = 0.013) for FB, whereby those with greater exposure performed worse. No other regression analyses within or across groups were significant.

CONCLUSIONS

These data suggest that RHI do not represent clinically meaningful changes on a multifaceted and multimodal concussion assessment battery. However, there may be subtle visual/vestibular impairments as observed by the associations between RHI and visual memory/TG among WSOC, RHI, and KD among FB.

Dependence on subconcussive impacts of brain metabolism in collision sport athletes: an MR spectroscopic study

Long term neurological impairments due to repetitive head trauma are a growing concern for collision sport athletes. American Football has the highest rate of reported concussions among male high school athletes, a position held by soccer for female high school athletes. Recent research has shown that subconcussive events experienced by collision sport athletes can be a further significant source of accrued damage. Collision sport athletes experience hundreds of subconcussive events in a single season, and these largely go uninvestigated as they produce no overt clinical symptoms. Continued participation by these seemingly uninjured athletes is hypothesized to increase susceptibility to diagnoseable brain injury. This study paired magnetic resonance spectroscopy with head impact monitoring to quantify the relationship between metabolic changes and head acceleration event characteristics in high school-aged male football and female soccer collision sport athletes. During the period of exposure to subconcussive events, asymptomatic male (football) collision sport athletes exhibited statistically significant changes in concentrations of glutamate+glutamine (Glx) and total choline containing compounds (tCho) in dorsolateral prefrontal cortex, and female (soccer) collision sport athletes exhibited changes in glutamate+glutamine (Glx) in primary motor cortex. Neurometabolic alterations observed in football athletes during the second half of the season were found to be significantly associated with the average acceleration per head acceleration events, being best predicted by the accumulation of events exceeding 50 g. These marked deviations in neurometabolism, in the absence of overt symptoms, raise concern about the neural health of adolescent collision-sport athletes and suggest limiting exposure to head acceleration events may help to ameliorate the risk of subsequent cognitive impairment.

Effect of Routine Sport Participation on Short-Term Clinical Neurological Outcomes: A Comparison of Non-Contact, Contact, and Collision Sport Athletes

OBJECTIVES

To compare pre-season to post-season changes on a battery of clinical neurological outcome measures between non-contact, contact, and collision sport athletes over multiple seasons of play.

METHODS

244 high school and collegiate athletes participating in multiple non-contact, contact, and collision sports completed standardized annual pre-season and post-season assessments over 1-4 years. Pre/post-season changes in 10 outcome measures assessing concussion symptoms, neurocognitive performance, and balance were compared between the groups using linear mixed models.

RESULTS

Small, but statistically significant overall pre/post-season change differences were present between the groups for Axon computerized neurocognitive test processing speed, attention, and working memory speed scores (Axon-PS, Axon-Att, Axon-WMS), as well as Balance Error Scoring System (BESS) total score. Small seasonal declines not exceeding reliable-change thresholds were observed in the collision sport group relative to the contact and non-contact groups for Axon-PS and Axon-Att scores. The collision and contact sport groups demonstrated less pre-/post-season improvement than the non-contact sport group for Axon-WMA and BESS, with less BESS improvement also observed in the collision sport group relative to the contact sport group. Overall, longitudinal performance on all 10 outcome measures remained stable in all 3 groups over 4 years.

CONCLUSION

Our findings do not necessarily support the notion that participation in sports associated with exposure to repetitive head impacts has clinically meaningful cumulative effects over the course of a season, nor over four consecutive seasons in high school and collegiate athletes.

Impact attenuation of male and female lacrosse helmets using a modal impulse hammer

It has been established that substantial negative changes in neurocognitive function can be observed in a large percentage of athletes who participate in contact sports such as soccer or football, motivating a need for improved safety systems. Head accelerations in men's lacrosse are similar to those in football and female lacrosse players experience high rates of concussions, necessitating better head protection in both sports. Previous studies have sought to evaluate the ability of modern football helmets to mitigate impacts both normal and oblique to the surface of the helmet using a system that quantifies both the input load and the resulting accelerations of a Hybrid III headform. This study quantifies the inputs and outputs of the helmet-Hybrid III headform system in order to compare the impact attenuation capability of two male and two female lacrosse helmets. Of those helmets tested, the better performing male helmet was the Schutt Stallion 650 and the better performing female helmet was the Hummingbird excepting device failure at the rear boss impact location, but football helmets still generally outperformed the lacrosse helmets tested here.

Repetitive Head Impacts in Youth Football: Description and Relationship to White Matter Structure

BACKGROUND

Few studies have examined white matter with diffusion tensor imaging in 8- to 12-year-old collision sport (CS) athletes.

HYPOTHESIS

Youth CS athletes will demonstrate change in brain fractional anisotropy (FA) after a season of CS compared with an age-matched noncollision sport (NCS) cohort, and the number, magnitude, and location of hits will correlate with changes in the brain determined via FA for CS athletes.

STUDY DESIGN

Prospective cohort study.

LEVEL OF EVIDENCE

Level 3.

METHODS

Thirty-five 8- to 12-year-old males in a youth tackle football league (CS) and 12 males from local swim teams (NCS) were recruited. Participants underwent brain magnetic resonance imaging with FA before and after the football season. Number, magnitude, and direction of head impacts were recorded for CS participants throughout the season.

RESULTS

A total of 1905 hits were recorded in the CS group for the season, 341 (17.9%) collected during 7 games and 1564 (82.1%) observed during 31 practices. No significant interaction between group (CS and NCS) and time (pre- and postseason) was observed for FA (P > 0.05). Correlation analysis revealed a significantly positive and moderate relationship between increase of left cingulate cortex (CgC) FA from pre- to postseason and the total magnitude of lateral head impacts (r = 0.40; P = 0.03).

CONCLUSION

There was no significant change in FA measurement of white matter integrity in a cohort of 8- to 12-year-old males after a season of youth football, nor was any difference detected in FA between youth football players and an age-matched cohort of swimmers. There was a significant correlation between total magnitude of hits sustained by youth football players and an increase in FA in the left CgC; whether this is adaptive or pathologic remains unknown.

CLINICAL RELEVANCE

These data can be used within the body of knowledge to counsel patients regarding the known risks of youth tackle football regarding brain health.

Laboratory Performance Evaluation of Pristine and Used Headgear for Girls' Lacrosse

Girls' lacrosse participation and head injury rates have increased within the past decade. In response, optional headgear was implemented following the recently developed ASTM International (ASTM) lacrosse headgear performance standards. It remains unknown how lacrosse headgear responds to blunt impacts after use. Our purpose was to compare the peak linear acceleration (PLA) between girls' lacrosse headgear conditions (pristine and used) during blunt impacts. Pristine headgear (n=10) were tested in their original condition and used headgear (n=10) were worn for an entire competitive season. A Cadex Monorail Impactor impacted all headgear following ASTM standards (F1446-15b, F2220-15, and F3137-15) in the required testing locations. A 2 x 7 repeated measures ANOVA compared PLA among headgear conditions and impact locations with a simple effects analysis planned comparison. There was no difference between headgear conditions for PLA (Pristine: 47.12 ± 13.92g; Used: 46.62 ± 14.84g; F = 2.11, p > 0.05). A main effect for impact location (F = 983.52, p < 0.01), and an interaction effect of condition and impact location (F = 12.79, p < 0.01) were observed. All headgear, regardless of condition, met the ASTM performance standard. This suggests that headgear performance may not degrade subsequent to a single season of high school girl's lacrosse.

Every hit matters: White matter diffusivity changes in high school football athletes are correlated with repetitive head acceleration event exposure

Recent evidence of short-term alterations in brain physiology associated with repeated exposure to moderate intensity subconcussive head acceleration events (HAEs), prompts the question whether these alterations represent an underlying neural injury. A retrospective analysis combining counts of experienced HAEs and longitudinal diffusion-weighted imaging explored whether greater exposure to incident mechanical forces was associated with traditional diffusion-based measures of neural injury—reduced fractional anisotropy (FA) and increased mean diffusivity (MD). Brains of high school athletes (N = 61) participating in American football exhibited greater spatial extents (or volumes) experiencing substantial changes (increases and decreases) in both FA and MD than brains of peers who do not participate in collision-based sports (N = 15). Further, the spatial extents of the football athlete brain exhibiting traditional diffusion-based markers of neural injury were found to be significantly correlated with the cumulative exposure to HAEs having peak translational acceleration exceeding 20 g. This finding demonstrates that subconcussive HAEs induce low-level neurotrauma, with prolonged exposure producing greater accumulation of neural damage. The duration and extent of recovery associated with periods in which athletes do not experience subconcussive HAEs now represents a priority for future study, such that appropriate participation and training schedules may be developed to minimize the risk of long-term neurological dysfunction.

•

Brain volumes evidencing injury are larger in football athletes than controls.

•

Spatial extent of decreased FA correlates with head acceleration event exposure.

•

Spatial extent of increased MD correlates with head acceleration event exposure.

Neuroimaging and Neuropsychological Studies in Sports-Related Concussions in Adolescents: Current State and Future Directions

Sports-related concussion, is a serious neurological concern that many adolescent athletes will face during their athletic careers. In some instances, the effects of sports-related head injury are long-lasting. Due to their still-developing brains, adolescents appear to be more vulnerable to long-term repercussions of these injuries. As all sports-related concussions are mild traumatic brain injuries (mTBI), this review we will examine the pathophysiology of mTBI, its acute effects and long-term risks from sustaining injury, and current and needed advancements in the areas of neuropsychological testing, accelerometer telemetry, and neuroimaging. Current methods do not adequately measure the extent of an injury that an athlete may sustain, potentially putting these athletes at a much greater risk for long-term effects. To better understand mTBI, neuropsychological testing best practices need to be developed, standardized, and implemented based on sound scientific evidence in order to be propagated as clinical guidelines. Wearable accelerometers can be used to assess thresholds for mTBI and cumulative effects of concussive and subconcussive injuries. Novel neuroimaging methods that can detect anatomical abnormalities and functional deficits with more specificity and sensitivity should be developed. Young athletes are particularly a vulnerable population warranting immediate and significant research aimed at protecting them against sports related injury and mitigating their long-term deficits.

Risk Factors for Initial and Subsequent Core or Lower Extremity Sprain or Strain Among Collegiate Football Players

CONTEXT

Exposure to game conditions and previous injury are known to increase the risk of injury, but little available evidence pertains to modifiable factors that may mediate dynamic control of body segments, such as core muscle endurance and neurocognitive capabilities.

OBJECTIVE

To identify potentially modifiable factors associated with the occurrence of a core or lower extremity sprain or strain during participation in football.

DESIGN

Prospective cohort study.

SETTING

National Collegiate Athletic Association Division I Football Bowl Subdivision football program.

PATIENTS OR OTHER PARTICIPANTS

All team members who participated for the duration of 1 season or both of 2 consecutive seasons (n = 142).

MAIN OUTCOME MEASURE(S)

Predictors of injury occurrence were derived from analysis of preparticipation data that included the results of front plank hold (FPH) and neurocognitive tests. Receiver operating characteristic analysis was used to establish binary classifications of injury risk. Logistic regression analyses were conducted to build multivariable injury-prediction models for optimal discriminatory power.

RESULTS

Exceptionally good discrimination between injured and noninjured participants was provided by models that included the results of the FPH and ImPACT neurocognitive tests. A high level of exposure to game conditions and injury during the preceding year magnified the effects of other risk factors. A model for identifying players with an elevated risk for injury occurrence during both of 2 consecutive seasons included FPH ≤120 seconds, verbal memory score ≤87, composite reaction time ≥560 milliseconds, and starter status. Having ≥2 of the 4 risk factors demonstrated 44% sensitivity and 91% specificity, with an odds ratio = 8.40.

CONCLUSIONS

Core muscle endurance and neurocognitive processes may both play important roles in generating anticipatory muscle stiffness during participation in collegiate football. These factors may be particularly important for players who sustained an injury during the previous year and those who have a high level of game exposure.

Elevated markers of brain injury as a result of clinically asymptomatic high-acceleration head impacts in high-school football athletes

OBJECTIVE

This prospective observational cohort study of high-school football athletes was performed to determine if high-acceleration head impacts (HHIs) that do not result in clinically diagnosed concussion still lead to increases in serum levels of biomarkers indicating traumatic brain injury (TBI) in asymptomatic athletes and to determine the longitudinal profile of these biomarkers over the course of the football season.

METHODS

Sixteen varsity high-school football athletes underwent baseline neurocognitive testing and blood sampling for the biomarkers tau, ubiquitin C-terminal hydrolase L1 (UCH-L1), neurofilament light protein (NF-L), glial fibrillary acidic protein (GFAP), and spectrin breakdown products (SBDPs). All athletes wore helmet-based accelerometers to measure and record head impact data during all practices and games. At various time points during the season, 6 of these athletes met the criteria for HHI (linear acceleration > 95g and rotational acceleration > 3760 rad/sec2); in these athletes a second blood sample was drawn at the end of the athletic event during which the HHI occurred. Five athletes who did not meet the criteria for HHI underwent repeat blood sampling following the final game of the season. In a separate analysis, all athletes who did not receive a diagnosis of concussion during the season (n = 12) underwent repeat neurocognitive testing and blood sampling after the end of the season.

RESULTS

Total tau levels increased 492.6% ± 109.8% from baseline to postsession values in athletes who received an HHI, compared with 164% ± 35% in athletes who did not receive an HHI (p = 0.03). Similarly, UCH-L1 levels increased 738.2% ± 163.3% in athletes following an HHI, compared with 237.7% ± 71.9% in athletes in whom there was no HHI (p = 0.03). At the end of the season, researchers found that tau levels had increased 0.6 ± 0.2 pg/ml (p = 0.003) and UCH-L1 levels had increased 144.3 ± 56 pg/ml (p = 0.002). No significant elevations in serum NF-L, GFAP, or SBDPs were seen between baseline and end-of-athletic event or end-of-season sampling (for all, p > 0.05).

CONCLUSIONS

In this pilot study on asymptomatic football athletes, an HHI was associated with increased markers of neuronal (UCH-L1) and axonal (tau) injury when compared with values in control athletes. These same markers were also increased in nonconcussed athletes following the football season.

Fluctuations in blood biomarkers of head trauma in NCAA football athletes over the course of a season

OBJECTIVE

Repetitive subconcussive head trauma is a consequence of participation in contact sports and may be linked to neurodegenerative diseases. The degree of neurological injury caused by subconcussive head trauma is not easily detectible, and this injury does not induce readily identifiable clinical signs or symptoms. Recent advancements in immunoassays make possible the detection and quantification of blood biomarkers linked to head trauma. Identification of a blood biomarker that can identify the extent of neurological injury associated with subconcussive head trauma may provide an objective measure for informed decisions concerning cumulative exposure to subconcussive head trauma. The purpose of the current study was to examine changes in the blood biomarkers of subconcussive head trauma over the course of an American football season.

METHODS

Thirty-five National Collegiate Athletic Association (NCAA) American football athletes underwent blood sampling throughout the course of a football season. Serial samples were obtained throughout the 2016 season, during which the number and magnitude of head impacts changed. Blood samples were analyzed for plasma concentrations of tau and serum concentrations of neurofilament light polypeptide (NF-L). Athletes were grouped based on their starter status, because athletes identified as starters are known to sustain a greater number of impacts. Between-group differences and time-course differences were assessed.

RESULTS

In nonstarters, plasma concentrations of tau decreased over the course of the season, with lower values observed in starters; this resulted in a lower area under the curve (AUC) (starters: 416.78 ± 129.17 pg/ml/day; nonstarters: 520.84 ± 163.19 pg/ml/day; p = 0.050). Plasma concentrations of tau could not be used to discern between starters and nonstarters. In contrast, serum concentrations of NF-L increased throughout the season as head impacts accumulated, specifically in those athletes categorized as starters. The higher serum concentrations of NF-L observed in starters resulted in a larger AUC (starters: 1605.03 ± 655.09 pg/ml/day; nonstarters: 1067.29 ± 272.33 pg/ml/day; p = 0.007). The AUC of the receiver operating characteristic curve analyses displayed fair to modest accuracy to identify athletes who were starters with the use of serum NF-L following periods of repetitive impacts.

CONCLUSIONS

The different patterns observed in serum NF-L and plasma tau concentrations provide preliminary evidence for the use of blood biomarkers to detect the neurological injury associated with repetitive subconcussive head trauma. Although further investigation is necessary, such findings might lay the foundation for the further development of an objective measure for the detection of neurological injury caused by subconcussive head trauma.

Head impact magnitudes that occur from purposeful soccer heading depend on the game scenario and head impact location

PURPOSE

This study quantified the linear and angular kinematics that result from purposeful heading during youth soccer games, and the influence of game scenario and head impact location on these magnitudes.

METHOD

This observational study recruited thirty-six female soccer players (13.4 ± 0.9 years old) from three elite youth soccer teams (U13, U14, U15) and followed for an entire soccer season. Players wore wireless sensors during each game to quantify head impact magnitudes. A total of 60 regular season games (20 games per team) were video recorded, and purposeful heading events were categorized by game scenario (e.g. throw in), and head impact location (e.g. front of head).

RESULTS

Game scenario had a statistically significant effect on the linear head acceleration, and rotational head velocity, that resulted from purposeful headers. Rotational velocity from purposeful headers varied significantly between head impact locations, with impacts to the top of the head (improper technique) resulting in larger peak rotational velocities than impacts to the front of the head (proper technique); this was also the case for the linear acceleration for punts.

CONCLUSION

Our findings suggest that the magnitude for both linear and angular head impact kinematics depend on the game scenario and head impact location. Headers performed with the top of the head (improper technique) result in larger rotational velocities compared to the front of the head (proper technique). Accordingly, youth players should be educated on how to execute proper heading technique to reduce head impact accelerations.

Verifying Head Impacts Recorded by a Wearable Sensor using Video Footage in Rugby League: a Preliminary Study

BACKGROUND

Rugby league is a full-contact collision sport with an inherent risk of concussion. Wearable instrumented technology was used to observe and characterize the level of exposure to head impacts during game play.

PURPOSE

To verify the impacts recorded by the x-patch™ with video analysis.

STUDY DESIGN

Observational case series.

METHODS

The x-patch™ was used on eight men's semi-professional rugby league players during the 2016 Newcastle Rugby League competition (five forwards and three backs). Game day footage was recorded by a trained videographer using a single camera located at the highest midfield location to verify the impact recorded by the x-patch™. Videographic and accelerometer data were time synchronized.

RESULTS

The x-patch™ sensors recorded a total of 779 impacts ≥ 20 g during the games, of which 732 (94.0%) were verified on video. In addition, 817 impacts were identified on video that did not record an impact on the sensors. The number of video-verified impacts ≥ 20 g, per playing hour, was 7.8 for forwards and 4.8 for backs (range = 3.9-19.0). Impacts resulting in a diagnosed concussion had much greater peak linear acceleration (M = 76.1 g, SD = 17.0) than impacts that did not result in a concussion (M = 34.2g, SD = 18.0; Cohen's d = 2.4).

CONCLUSIONS

The vast majority (94%) of impacts ≥ 20 g captured by the x-patch™ sensor were video verified in semi-professional rugby league games. The use of a secondary source of information to verify impact events recorded by wearable sensors is beneficial in clarifying game events and exposure levels.

Positron emission tomography of tau in Iraq and Afghanistan Veterans with blast neurotrauma

Military personnel are often exposed to multiple instances of various types of head trauma. As a result, there has been increasing concern recently over identifying when head trauma has resulted in a brain injury and what, if any, long-term consequences those brain injuries may have. Efforts to develop equipment to protect soldiers from these long-term consequences will first require understanding the types of head trauma that are likely responsible. In this study, we sought to identify the types of head trauma most likely to lead to the deposition of tau, a protein identified as a likely indicator of long-term negative consequences of brain injury. To define the types of head trauma in a military population, we applied a factor analysis to interviews from a larger cohort of 428 Veterans enrolled in the Translational Research Center for Traumatic Brain Injury and Stress Disorders. Three factors were identified: Blast Exposure, Symptom Duration, and Blunt Concussion. Sixteen male Veterans from this study and one additional male civilian (aged 25-69, mean 35.2 years) underwent simultaneous positron emission tomography/magnetic resonance imaging using a tracer that binds to tau protein, the ligand T807/AV-1451 (Flortaucipir). Standard uptake value ratios to the isthmus of the cingulate were calculated from a 20-minute time frame 70 min post-injection. We found that tracer uptake throughout the brain was associated with Blast Exposure factor beta weights, but not with either Symptom Duration or Blunt Concussion. Associations with uptake were located primarily in the cerebellar, occipital, inferior temporal and frontal regions. The data suggest that in this small, relatively young cohort of Veterans, elevated T807/AV-1451 uptake is associated with exposure to blast neurotrauma. These findings are unanticipated, as they do not match histopathological descriptions of tau pathology associated with head trauma. Continued work will be necessary to understand the nature of the regional T807/AV-1451 uptake and any associations with clinical symptoms.

New generation of headgear for rugby: impact reduction of linear and rotational forces by a viscoelastic material-based rugby head guard

Objectives

In the aim to develop a usable and wearable head guard for rugby that could reduce impact energy and lessen the likelihood of concussive and subconcussive injury during play, a combination of viscoelastic materials was employed to develop a guard with similar dimensions to those currently used in international rugby.

Methods

The head guard was tested for impact energy reduction following linear acceleration, using drop tests, as required by World Rugby. The head guard was also subjected to pendulum tests, allowing acceleration to be simultaneously measured on two headforms, as well as repeated impacts to mimic ageing and repeated use. Impact following rotational acceleration was determined at two impact locations and at three impact velocities.

Results

The viscoelastic head guard (N-Pro) was shown to reduce linear impacts by up to 75% in comparison to the use of a commercially available rugby head guard and repeated impacts did not impair the attenuation of impact energy. Rotational impact energy was also reduced by an average of 34% across three speeds and two sites of impact test sites, in comparison to tested bare headforms.

Conclusions

This heralds a new generation of soft-shelled headgear that could help reduce two primary risk factors in sports-induced mild traumatic brain injury: linear and rotational impacts to the head.

Imaging findings after acute sport-related concussion in American football players: A systematic review

Sport-related concussion (SRC) has emerged as a major public health problem. The results of brain imaging studies following SRC have raised questions about long-term neurologic health, but the clinical implications of these findings remain unknown. A systematic review of brain imaging findings after SRC was performed utilizing the following inclusion criteria: football players, brain imaging within 6 months of SRC, and sample size >5. Studies were assessed for: 1) methodology, 2) imaging outcomes, and 3) number of positive statistical comparisons. Imaging was classified as immediate (≤1 week post-injury) or subacute (>1 week to 6 months post-injury). Eleven studies met inclusion criteria. Eight of the 11 studies conducted a total of 809 comparisons of brain function, of which 149 (18%) were statistically significant. Nine of the 11 studies (82%) reported positive immediate findings, but were more likely to be subject to recall bias (86% vs. 0%) and to lack baseline advanced brain imaging (78% vs. 50%) than negative studies. Only 3 of 9 studies that reported subacute findings (33%) reported positive results, and these positive studies were also more likely to be subject to recall bias (100% vs. 40%) and to lack baseline advanced brain imaging (100% vs. 67%) than negative studies. The results of the study demonstrate the transitory nature of positive imaging findings and methodological limitations that complicate study interpretation. Further research is required to correlate imaging findings with clinical outcomes.

Protection Before Impact: the Potential Neuroprotective Role of Nutritional Supplementation in Sports-Related Head Trauma

Even in the presence of underreporting, sports-related concussions/mild traumatic brain injuries (mTBI) are on the rise. In the absence of proper diagnosis, an athlete may return to play prior to full recovery, increasing the risk of second-impact syndrome or protracted symptoms. Recent evidence has demonstrated that sub-concussive impacts, those sustained routinely in practice and competition, result in a quantifiable pathophysiological response and the accumulation of both concussive and sub-concussive impacts sustained over a lifetime of sports participation may lead to long-term neurological impairments and an increased risk of developing neurodegenerative diseases. The pathophysiological, neurometabolic, and neurochemical cascade that initiates subsequent to the injury is complex and involves multiple mechanisms. While pharmaceutical treatments may target one mechanism, specific nutrients and nutraceuticals have been discovered to impact several pathways, presenting a broader approach. Several studies have demonstrated the neuroprotective effect of nutritional supplementation in the treatment of mTBI. However, given that many concussions go unreported and sub-concussive impacts result in a pathophysiological response that, too, may contribute to long-term brain health, protection prior to impact is warranted. This review discusses the current literature regarding the role of nutritional supplements that, when provided before mTBI and traumatic brain injury, may provide neurological protection.

Comparison of Head Impact Exposure Between Concussed Football Athletes and Matched Controls: Evidence for a Possible Second Mechanism of Sport-Related Concussion

Studies of football athletes have implicated repetitive head impact exposure in the onset of cognitive and brain structural changes, even in the absence of diagnosed concussion. Those studies imply accumulating damage from successive head impacts reduces tolerance and increases risk for concussion. Support for this premise is that biomechanics of head impacts resulting in concussion are often not remarkable when compared to impacts sustained by athletes without diagnosed concussion. Accordingly, this analysis quantified repetitive head impact exposure in a cohort of 50 concussed NCAA Division I FBS college football athletes compared to controls that were matched for team and position group. The analysis quantified the number of head impacts and risk weighted exposure both on the day of injury and for the season to the date of injury. 43% of concussed athletes had the most severe head impact exposure on the day of injury compared to their matched control group and 46% of concussed athletes had the most severe head impact exposure for the season to the date of injury compared to their matched control group. When accounting for date of injury or season to date of injury, 72% of all concussed athletes had the most or second most severe head impact exposure compared to their matched control group. These trends associating cumulative head impact exposure with concussion onset were stronger for athletes that participated in a greater number of contact activities. For example, 77% of athletes that participated in ten or more days of contact activities had greater head impact exposure than their matched control group. This unique analysis provided further evidence for the role of repetitive head impact exposure as a predisposing factor for the onset of concussion. The clinical implication of these findings supports contemporary trends of limiting head impact exposure for college football athletes during practice activities in an effort to also reduce risk of concussive injury.

Cerebral Autoregulation Is Disrupted Following a Season of Contact Sports Participation

Repetitive subconcussive head impacts across a season of contact sports participation are associated with a number of deficits in brain function. To date, no research has investigated the effect of such head impact exposure on dynamic cerebral autoregulation (dCA). To address this issue, 179 elite, junior-level (age 19.6 ± 1.5 years) contact sport (ice hockey, American football) athletes were recruited for pre-season testing. Fifty-two non-concussed athletes returned for post-season testing. Fifteen non-contact sport athletes (age 20.4 ± 2.2) also completed pre- and postseason testing. dCA was assessed via recordings of beat-by-beat mean arterial pressure (MAP) and middle cerebral artery blood velocity (MCAv) using finger photoplethysmography and transcranial Doppler ultrasound, respectively, during repetitive squat-stand maneuvers at 0.05 and 0.10 Hz. Transfer function analysis was used to determine Coherence (correlation), Gain (response amplitude), and Phase (response latency) of the MAP-MCAv relationship. Results showed that in contact sport athletes, Phase was reduced (p = 0.027) and Gain increased (p < 0.001) at post-season compared to pre-season during the 0.10 Hz squat-stand maneuvers, indicating cerebral autoregulatory impairment in both the latency and magnitude of the response. Changes in Phase were greater in athletes experiencing higher numbers and severity of head impacts. By contrast, no changes in dCA were observed in non-contact sport controls. Taken together, these results demonstrate that repetitive subconcussive head impacts occurring across a season of contact sports participation are associated with exposure-dependent impairments in the cerebrovascular pressure-buffering system capacity. It is unknown how long these deficits persist or if they accumulate year-over-year.

Effect of Impact Mechanism on Head Accelerations in Men's Lacrosse Athletes

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 F_10,306 = 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.

Head Impact Exposure in Practices Correlates With Exposure in Games for Youth Football Players

This study aimed to compare head impact exposures between practices and games in football players ages 9 to 14 years, who account for approximately 70% of all football players in the United States. Over a period of 2 seasons, 136 players were enrolled from 3 youth programs, and 49,847 head impacts were recorded from 345 practices and 137 games. During the study, individual players sustained a median of 211 impacts per season, with a maximum of 1226 impacts. Players sustained 50th (95th) percentile peak linear acceleration of 18.3 (46.9) g, peak rotational acceleration of 1305.4 (3316.6) rad·s-2, and Head Impact Technology Severity Profile of 13.7 (24.3), respectively. Overall, players with a higher frequency of head impacts at practices recorded a higher frequency of head impacts at games (P < .001, r2 = .52), and players who sustained a greater average magnitude of head impacts during practice also recorded a greater average magnitude of head impacts during games (P < .001). The youth football head impact data quantified in this study provide valuable insight into the player exposure profile, which should serve as a key baseline in efforts to reduce injury.

Investigating the effects of subconcussion on functional connectivity using mass-univariate and multivariate approaches

There are concerns about the effects of subconcussive head impacts in sport, but the effects of subconcussion on brain connectivity are not well understood. We hypothesized that college football players experience changes in brain functional connectivity not found in athletes competing in lower impact sports or healthy controls. These changes may be spatially heterogeneous across participants, requiring analysis methods that go beyond mass-univariate approaches commonly used in functional MRI (fMRI). To test this hypothesis, we analyzed resting-state fMRI data from college football (n = 15), soccer (n = 12), and lacrosse players (n = 16), and controls (n = 29) collected at preseason and postseason time points. Regional homogeneity (ReHo) and degree centrality (DC) were calculated as measures of local and long-range functional connectivity, respectively. Standard voxel-wise analysis and paired support vector machine (SVM) classification studied subconcussion's effects on local and global functional connectivity. Voxel-wise analyses yielded minimal findings, but SVM classification had high accuracy for college football's ReHo (87%, p = 0.009) and no other group. The findings suggest subconcussion results in spatially heterogeneous changes in local functional connectivity that may only be detectible with multivariate analyses. To determine if voxel-wise and SVM analyses had similar spatial patterns, region-average t-statistic and SVM weight values were compared using a measure of ranking distance. T-statistic and SVM weight rankings exhibited significantly low ranking distance values for all groups and metrics, demonstrating that the analyses converged on a similar underlying effect. Overall, this research suggests that subconcussion in football may produce local functional connectivity changes similar to concussion.

Cross-sectional evaluation of visuomotor tracking performance following subconcussive head impacts

BACKGROUND

Repeated mild traumatic brain injury (mTBI) has been associated with increased risk of degenerative neurological disorders. While the effects of mTBI and repeated injury are known, studies have only recently started examining repeated subconcussive impacts, impacts that do not result in a clinically diagnosed mTBI. In these studies, repeated subconcussive impacts have been connected to cognitive performance and brain imaging changes.

OBJECTIVE

Recent research suggests that performance on a visuomotor tracking (VMT) task may help improve the identification of mTBI. The goal of this study was to investigate if VMT performance is sensitive to the cumulative effect of repeated subconcussive head impacts in collegiate men's lacrosse players.

METHODS

A cross-sectional, prospective study was completed with eleven collegiate men's lacrosse players. Participants wore helmet-mounted sensors and completed VMT and reaction time assessments. The relationship between cumulative impact metrics and VMT metrics were investigated.

RESULTS

In this study, VMT performance correlated with repeated subconcussive head impacts; individuals approached clinically diagnosed mTBI-like performance as the cumulative rotational velocity they experienced increased.

CONCLUSION

This suggests that repeated subconcussive impacts can result in measurable impairments and indicates that visuomotor tracking performance may be a useful tool for monitoring the effects of repeated subconcussive impacts.

Head impacts and cognitive performance in men's lacrosse

OBJECTIVES

The purpose of this investigation was to record head impacts and assess cognitive function throughout a NCAA Division III men's lacrosse season.

METHODS

Fifteen NCAA Div III men's lacrosse players (age = 21.1 ± 1.5 years; height = 179 ± 7.00cm; weight = 80.74 ± 8.00kg) wore Smart Impact Monitors (SIM) (Triax Technologies, Inc., Norwalk, CT) within headbands, in 28 practices and 9 home games of one season. The SIM devices communicated with the Triax Technologies SKYi, which confirmed activated SIMs and obtained data of linear acceleration, rotational acceleration, rotational velocity, direction, and location of each head impact. A minimum threshold of 15g of force was set for head impacts to register with the SIMs. The Comprehensive Trail Making Test and Stroop Color and Word Test were administered at preseason, midseason, and postseason to assess cognitive function performance.

RESULTS

There was no significant difference found between all measures of frequency and magnitude of head impacts between games and practices. There was also no significant difference for peak linear acceleration of head impacts between different positions and no significant difference between the magnitude of force and the location of impact on the head. There was a significant increase in CTMT performance from preseason to midseason, from midseason to postseason, and preseason to postseason. There was no significant difference in Stroop test performance throughout the season.

CONCLUSION

Subconcussive head impacts in men's lacrosse appear to occur at the same magnitude in practices and games, and do not appear to be position dependent, nor head location dependent. Men's lacrosse athletes' cognitive function as measured by the CTMT, can improve, while cognitive function as measured by the Stroop test remained unchanged.

Alzheimer's Dementia due to Suspected CTE from Subconcussive Head Impact

Chronic traumatic encephalopathy (CTE) has been receiving increasing attention due to press coverage of professional football players. The devastating sequelae of CTE compel us to aim for early diagnosis and treatment. However, by current standards, CTE is challenging to diagnose. Clear clinical diagnostic criteria for CTE have not been established. Only recently, pathological diagnostic criteria have been recognized, but postmortem diagnosis is too late. Reliable biomarkers are not available. By imaging criteria, cavum septum pellucidum has been the only consistent identifiable MRI finding. Because of the imprecise nature of diagnosis based on clinical suspicion, physicians must become cognizant of the broad spectrum of presentations of CTE. With this awareness, appropriate workup can be initiated. CTE can present with early symptoms of emotional changes or late symptoms with memory decline and dementia. Here we present an unusual case of a patient with Alzheimer's disease secondary to suspected CTE that stems from subconcussive head impacts presenting with severe memory and MRI changes. Clinicians should be aware of this presentation and consider CTE in their differential diagnoses while undergoing workup of memory disorders.

The role of subconcussive impacts on sway velocities in Division I men's lacrosse players

Head impacts resulting in a concussion negatively affect the vestibular system, but little is known about the effect of subconcussive impacts on this system. This study's objective was to determine if subconcussive head impacts sustained over one competitive lacrosse season, effect sway velocity. Healthy Division I male lacrosse players (n = 33; aged 19.52 ± 1.20 years) wore instrumented helmets to track head impact exposures. At the beginning and end of the season the players completed an instrumented Balance Error Scoring System assessment to assess sway velocity. Score differentials were correlated to the head impact exposure data collected via instrumented helmets when averaged within participant. Paired samples t-tests revealed a post-season increase in sway velocity on the double leg stance, firm surface (p = 0.002, d = 0.59); tandem stance, firm surface (p = 0.033, d = 0.39) and double leg, foam surface (p = 0.014, d = 0.45) A significant correlation was found between change in tandem stance, firm surface sway velocities and linear acceleration (p < 0.001, r = 0.65). It appears subconcussive impacts may result in tandem stance balance deficits. Repetitive head impacts may negatively affect sway velocity, even in the absence of a diagnosed concussion injury.

Verbal Memory Deficits in OEF/OIF/OND Veterans Exposed to Blasts at Close Range

OBJECTIVES

This study investigated the relationship between close proximity to detonated blast munitions and cognitive functioning in OEF/OIF/OND Veterans.

METHODS

A total of 333 participants completed a comprehensive evaluation that included assessment of neuropsychological functions, psychiatric diagnoses and history of military and non-military brain injury. Participants were assigned to a Close-Range Blast Exposure (CBE) or Non-Close-Range Blast Exposure (nonCBE) group based on whether they had reported being exposed to at least one blast within 10 meters.

RESULTS

Groups were compared on principal component scores representing the domains of memory, verbal fluency, and complex attention (empirically derived from a battery of standardized cognitive tests), after adjusting for age, education, PTSD diagnosis, sleep quality, substance abuse disorder, and pain. The CBE group showed poorer performance on the memory component. Rates of clinical impairment were significantly higher in the CBE group on select CVLT-II indices. Exploratory analyses examined the effects of concussion and multiple blasts on test performance and revealed that number of lifetime concussions did not contribute to memory performance. However, accumulating blast exposures at distances greater than 10 meters did contribute to poorer performance.

CONCLUSIONS

Close proximity to detonated blast munitions may impact memory, and Veterans exposed to close-range blast are more likely to demonstrate clinically meaningful deficits. These findings were observed after statistically adjusting for comorbid factors. Results suggest that proximity to blast should be considered when assessing for memory deficits in returning Veterans. Comorbid psychiatric factors may not entirely account for cognitive difficulties. (JINS, 2018, 24, 466-475).

A systematic review of neuroimaging findings in children and adolescents with sports-related concussion

BACKGROUND

Sport-related concussion (SRC) generally does not result in structural anomalies revealed through clinical imaging techniques such as MRI and CT. While advanced neuroimaging techniques offer another avenue to investigate the subtle alterations following SRC, the current pediatric literature in this area has yet to be reviewed. The aim of this review is to systematically explore the literature on magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), functional magnetic resonance imaging (fMRI), and cortical thickness following SRC in children and adolescents.

METHODS

A systematic Pubmed search using the preferred reporting items for systematic reviews and meta-analysis guidelines was conducted independently for each neuroimaging method. Studies were screened for inclusion based on pre-determined criteria.

RESULTS

A total of 26 studies were included (MRS = 4, DTI = 10, fMRI = 11, cortical thickness = 1). A total of 16 studies were conducted solely with male athletes, while 10 studies recruited an unequal number of male and female athletes.

CONCLUSIONS

While MRI and CT are generally unrevealing, advanced neuroimaging techniques demonstrated neurometabolic, microstructural, and functional alterations following SRC in athletes younger than 19 years of age in the acute, subacute, and chronic phases of recovery. However, more studies are needed to fully understand the impact of SRC on the developing brain in children and adolescents.

Effect of Head Impact Exposures on Changes in Cognitive Testing

Background

Gaining a better understanding of head impact exposures may lead to better comprehension of the possible effects of repeated impact exposures not associated with clinical concussion.

Purpose

To assess the correlation between head impacts and any differences associated with cognitive testing measurements pre- and postseason.

Study Design

Case-control study; Level of evidence, 3.

Methods

A total of 34 National Collegiate Athletic Association Division I men's lacrosse players wore lacrosse helmets instrumented with an accelerometer during the 2014 competitive season and were tested pre- and postseason with the Sport Concussion Assessment Tool (SCAT 3) and Concussion Vital Signs (CVS) computer-based neurocognitive tests. The number of head impacts >20g and results from the 2 cognitive tests were analyzed for differences and correlation.

Results

There was no significant difference between pre- and postseason SCAT 3 scores, although a significant correlation between pre- and postseason cognitive scores on the SCAT 3 and total number of impacts sustained was noted (r = -0.362, P = .035). Statistically significant improvements on half of the CVS testing components included visual reaction time (P = .037, d = 0.37), reaction time (P = .001, d = 0.65), and simple reaction time (P = .043, d = 0.37), but no correlation with head impacts was noted.

Conclusion

This study did not find declines in SCAT 3 or CVS scores over the course of a season among athletes who sustained multiple head impacts but no clinical concussion. Thus, it could not be determined whether there was no cognitive decline among these athletes or whether there may have been subtle declines that could not be measured by the SCAT 3 or CVS.

Neuromechanical Considerations for Postconcussion Musculoskeletal Injury Risk Management

Recent epidemiological studies have documented increased susceptibility to musculoskeletal injury after sport-related concussion, which raises questions about the adequacy of current clinical practices to ensure safe return to sport. A growing body of evidence derived from advanced neuroimaging and neurological assessment methods strongly suggests that mild traumatic brain injury has long-lasting adverse effects that persist beyond resolution of clinical symptoms. Plausible interrelationships among postconcussion changes in brain structure and function support the rationale for specific methods of clinical assessment and training to target the interaction of cognitive and motor function for reduction of musculoskeletal injury risk after concussion. The findings of preliminary clinical studies are presented to support suggested strategies for reduction of postconcussion musculoskeletal injury risk, and to identify novel approaches that we consider worthy areas for further research.

Subconcussive Blows to the Head: A Formative Review of Short-term Clinical Outcomes

BACKGROUND

Given questions about "lower thresholds" for concussion, as well as possible effects of repetitive concussion and chronic traumatic encephalopathy (CTE), and associated controversy, there is increasing interest in "subconcussive" blows and their potential significance.

OBJECTIVE

A formative review with critical examination of the developing literature on subconcussive blows in athletes with an emphasis on clinical outcomes.

METHODS

Studies of biomechanical, performance and/or symptom-based, and neuroimaging data were identified via PubMed search and critically reviewed. Five studies of symptom reporting/performance and 4 studies of neuroimaging were included.

RESULTS

The relation between biomechanical parameters and diagnosed concussion is not straightforward (ie, it is not the case that greater and more force leads to more severe injury or cognitive/behavioral sequelae). Neuropsychological studies of subconcussive blows within a single athletic season have failed to demonstrate any strong and consistent relations between number and severity of subconcussive events and cognitive change. Recent studies using neuroimaging have demonstrated a potential cumulative effect of subconcussive blows, at least in a subset of individuals.

CONCLUSION

Human studies of the neurological/neuropsychological impact of subconcussive blows are currently quite limited. Subconcussive blows, in the short-term, have not been shown to cause significant clinical effects. To date, findings suggest that any effect of subconcussive blows is likely to be small or nonexistent, perhaps evident in a subset of individuals on select measures, and maybe even beneficial in some cases. Longer-term prospective studies are needed to determine if there is a cumulative dose effect.

No Seasonal Changes in Cognitive Functioning Among High School Football Athletes: Implementation of a Novel Electrophysiological Measure and Standard Clinical Measures

OBJECTIVE

To evaluate neuroelectric and cognitive function relative to a season of football participation. Cognitive and neuroelectric function declines are hypothesized to be present in football athletes.

DESIGN

Observational.

SETTING

Athletic fields and research laboratory.

PATIENTS (OR PARTICIPANTS)

Seventy-seven high school athletes (15.9 + 0.9 years, 178.6 + 7.2 cm, 74.4 + 14.7 kg, and 0.8 + 0.8 self-reported concussions) participating in football (n = 46) and noncontact sports (n = 31).

INTERVENTIONS (OR ASSESSMENT OF RISK FACTORS)

All athletes completed preseason, midseason, and postseason assessments of cognitive and neuroelectric function, self-reported symptoms, and quality of life. All athletes participated in their respective sports without intervention, while head impact exposure in football athletes was tracked using the Head Impact Telemetry System.

MAIN OUTCOME MEASURES

Cognitive performance was based on Cogstate computerized cognitive assessment tool processing speed, attention, learning, working memory speed, and working memory accuracy scores. ElMindA brain network activation amplitude, synchronization, timing and connectivity brain network activation scores demarcated neuroelectric performance. Quality of life was assessed on the Health Behavior Inventory and Satisfaction with Life Scale and symptoms on the SCAT3 inventory.

RESULTS

Football and control sport athletes did not show declines in cognitive or neuroelectric function, quality-of-life measures, or symptom reports across a season of sport participation.

CONCLUSIONS

These findings refute the notion that routine football participation places athletes at risk for acute cognitive declines. The lack of impairment may be associated with no association with head impacts and cognitive function, increased physical activity offsetting any declines, and/or test sensitivity. How these findings are associated with long-term cognitive function is unknown.

Concussion, microvascular injury, and early tauopathy in young athletes after impact head injury and an impact concussion mouse model

The mechanisms underpinning concussion, traumatic brain injury, and chronic traumatic encephalopathy, and the relationships between these disorders, are poorly understood. We examined post-mortem brains from teenage athletes in the acute-subacute period after mild closed-head impact injury and found astrocytosis, myelinated axonopathy, microvascular injury, perivascular neuroinflammation, and phosphorylated tau protein pathology. To investigate causal mechanisms, we developed a mouse model of lateral closed-head impact injury that uses momentum transfer to induce traumatic head acceleration. Unanaesthetized mice subjected to unilateral impact exhibited abrupt onset, transient course, and rapid resolution of a concussion-like syndrome characterized by altered arousal, contralateral hemiparesis, truncal ataxia, locomotor and balance impairments, and neurobehavioural deficits. Experimental impact injury was associated with axonopathy, blood-brain barrier disruption, astrocytosis, microgliosis (with activation of triggering receptor expressed on myeloid cells, TREM2), monocyte infiltration, and phosphorylated tauopathy in cerebral cortex ipsilateral and subjacent to impact. Phosphorylated tauopathy was detected in ipsilateral axons by 24 h, bilateral axons and soma by 2 weeks, and distant cortex bilaterally at 5.5 months post-injury. Impact pathologies co-localized with serum albumin extravasation in the brain that was diagnostically detectable in living mice by dynamic contrast-enhanced MRI. These pathologies were also accompanied by early, persistent, and bilateral impairment in axonal conduction velocity in the hippocampus and defective long-term potentiation of synaptic neurotransmission in the medial prefrontal cortex, brain regions distant from acute brain injury. Surprisingly, acute neurobehavioural deficits at the time of injury did not correlate with blood-brain barrier disruption, microgliosis, neuroinflammation, phosphorylated tauopathy, or electrophysiological dysfunction. Furthermore, concussion-like deficits were observed after impact injury, but not after blast exposure under experimental conditions matched for head kinematics. Computational modelling showed that impact injury generated focal point loading on the head and seven-fold greater peak shear stress in the brain compared to blast exposure. Moreover, intracerebral shear stress peaked before onset of gross head motion. By comparison, blast induced distributed force loading on the head and diffuse, lower magnitude shear stress in the brain. We conclude that force loading mechanics at the time of injury shape acute neurobehavioural responses, structural brain damage, and neuropathological sequelae triggered by neurotrauma. These results indicate that closed-head impact injuries, independent of concussive signs, can induce traumatic brain injury as well as early pathologies and functional sequelae associated with chronic traumatic encephalopathy. These results also shed light on the origins of concussion and relationship to traumatic brain injury and its aftermath.awx350media15713427811001.

Sensing Passive Eye Response to Impact Induced Head Acceleration Using MEMS IMUs

The eye may act as a surrogate for the brain in response to head acceleration during an impact. Passive eye movements in a dynamic system are sensed by microelectromechanical systems (MEMS) inertial measurement units (IMU) in this paper. The technique is validated using a three-dimensional printed scaled human skull model and on human volunteers by performing drop-and-impact experiments with ribbon-style flexible printed circuit board IMUs inserted in the eyes and reference IMUs on the heads. Data are captured by a microcontroller unit and processed using data fusion. Displacements are thus estimated and match the measured parameters. Relative accelerations and displacements of the eye to the head are computed indicating the influence of the concussion causing impacts.

Comparison of baseline ImPACT performance in amateur motocross riders to football and basketball athletes

PRIMARY OBJECTIVE

The American Motorcyclist Association requires professional riders to undergo baseline computerized neurocognitive testing (CNT) using the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) test for concussion management. It is recommended this practice be expanded to the amateur level, but limited research has explored whether baseline testing is necessary for youth when normative data is available. This study evaluates the utility of baseline testing for amateur riders by comparing their performance to those of traditional youth sports comprising normative datasets.

DESIGN/METHODS

An cross-sectional study comparing amateur motocross (N = 100) riders matched by age and sex to football (N = 100) and basketball (N = 100) athletes performance on baseline ImPACT testing.

RESULTS

ANCOVAs revealed a significant medium effect of group on measures of visual motor speed (F = 11.25, p < 0.001) and reaction time (F = 13.61, p < 0.001). Post hoc analyses revealed that motocross riders were significantly slower compared to football and basketball athletes. There were no significant differences (p > .05) between sport on measures of memory or symptoms.

CONCLUSIONS

Youth motocross riders performed significantly slower on speed measures compared to football and basketball athletes, providing preliminary support for the expansion of baseline ImPACT testing to the amateur level.

Neurologic benefits of sports and exercise

Traumatic brain injury (TBI) is associated with several pathophysiologic changes, including: neurostructural alterations; molecular changes with shifts in circulating neurotrophins; impaired neural metabolism; changes in cerebrovascular autoregulation, vasoreactivity, and neurovascular coupling; and alterations in functional brain connectivity. In animal models of TBI, aerobic exercise reduces neuronal injury, promotes neuronal survival, and enhances the production of neuroprotective trophic factors. However, the timing of exercise initiation is an important consideration as early exercise in the acute postinjury period may impede recovery mechanisms, although evidence for this in humans is lacking. Though human clinical studies are limited, aerobic exercise post-TBI engages cerebrovascular mechanisms and may impart neurophysiologic benefits to mitigate post-TBI pathophysiologic changes. Additionally, subsymptom threshold exercise in humans has been demonstrated to be safe, feasible, and effective in decreasing symptom burden in individuals with mild TBI, and to counteract the detrimental effects of prolonged inactivity, subsequent physical deconditioning, and its negative emotional sequelae. This chapter will explore the potential role of aerobic exercise in neurorecovery after TBI.

Subconcussive trauma

Even impacts that do not immediately elicit symptoms of a concussion can induce changes in neural integrity. Because these so-called "subconcussive" head acceleration events, or head impact exposures, do not elicit identifiable symptoms, athletes continue to participate with unclear consequences. Neuroimaging studies reveal that neurologic changes, including inflammation, are associated with repetitive head impact exposures. Given that brain changes have been observed in athletes following repetitive head impact exposure, it is important to understand better and mitigate against this phenomenon. It is important to transition from the metric of concussion alone to one that includes repetitive head impact exposure, including the development of models that address why brain integrity may be compromised, who is at risk, and how to mitigate the risk of such exposure. Future work can include a health-monitoring framework to effect change and promote athlete safety.