Biomechanics of Sport Concussion: Quest for the Elusive Injury Threshold

Video-Based Analysis of Suspected Concussions in Slap Fighting: Incidence and Characteristics

OBJECTIVE

Despite the high frequency of head impacts in slap fighting, little is known about suspected concussions in this sport. This study examined the frequency and characteristics of observable signs of suspected concussions in slap fighting among male athletes.

SETTING

Video-based analysis.

PARTICIPANTS

Athletes who participated in official male power slap matches from January 1, 2023 to June 31, 2024.

DESIGN

Video footage of all official male power slap matches during the study period was retrospectively analyzed by 3 sports medicine specialists experienced in sports injuries.

MAIN MEASURES

The frequency, total number, and types of observable signs of suspected concussion, and whether the fight continued after signs of suspected concussion were observed.

RESULTS

A total of 115 fights (97.5%) during the study period were available for video review. Of these, 40 (38.4%) resulted in knockouts and 21 (18.3%) in technical knockouts. Observable signs of suspected concussion were observed in 79.1% of fights, averaging 1.41 concussion signs per fight, and 0.31 per slap. Forty-eight (52.7%) of the fights with signs of suspected concussion continued following observed concussion signs.

CONCLUSION

The frequency, early identification, and management of suspected concussions in slap fighting should be prioritized, with further studies combining clinical assessments strongly recommended.

Effects of sleep symptomatology post-concussion on return to sport in collegiate athletes

OBJECTIVE

To describe the relationship between sleep-symptom severity and number of days to return to play following concussion in student-athletes.

DESIGN

Case series.

SETTING

A D1 NCAA university athletic department (institutional care).

PARTICIPANTS

The study enrolled 84 varsity athletes who suffered a sport-related concussion at the university from 2015 to 2021.

INDEPENDENT VARIABLES

Prior concussion(s), total symptom burden, and sleep symptomatology (sleeping more, sleeping less, trouble falling asleep, drowsiness, and fatigue) scores as reported using Post-Concussion Symptom Scale from the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT).

MAIN OUTCOME MEASURE

The number of days an athlete took to return to play following concussion.

RESULTS

Individuals who reported trouble falling asleep, sleeping less, fatigue, and drowsiness took significantly longer to return to play following concussion than individuals who did not report such symptoms (F1,102 = 34.12, p < 0.0001).

CONCLUSIONS

Sleep symptomatology present after concussion is predictive of days until return to sport. This study demonstrates the importance of sleep symptomatology post-concussion for athletes.

Head Impacts in the Top 1% by Peak Linear Acceleration and/or Work Cause Immediate Concussion Signs and 'Check Engine' Responses in Military Service Members and Civilian Athletes

PURPOSE

Historically, head impact monitoring sensors have suffered from single impact measurement errors, leading to their data described by clinical experts as 'clinically irrelevant.' The purpose of this study was to use an accurate impact monitoring mouthguard system and (1) define head impact distributions for military service members and civilians and (2) determine if there was a dose-response relationship between accurately measured head impact magnitudes versus observations of concussion signs.

METHODS

A laboratory-calibrated commercial impact monitoring mouthguard system, along with video and hardware to confirm the sensor was on the teeth during impacts, was used to acquire 54,602 head acceleration events (HAE) in 973 military and civilian subjects over 3,449 subject days.

RESULTS

There were 17,551 head impacts (32% of HAE) measured with peak linear acceleration (PLA) > 10 g and 37,051 low-g events (68% of HAE) in the range of activities of daily living < 10 g PLA. The median of all HAE and of all head impacts was 8 g/15 g PLA and 1 J/4 J Work, respectively. The top 1% of head impacts were above 47 g and 32 J, respectively. There were fifty-six (56) head impacts where at least one clinical indicator of a concussion sign was observed. All the clinical indicator impacts were in the top 1% by magnitude of PLA, Work, or both. The median magnitude of these 'check engine' impacts was 58 g and 48 J. This median magnitude was substantially larger than the median of all HAE as well as the median of all head impacts.

CONCLUSION

This study shows a correlation between single head impacts in the top 1% by peak linear acceleration and/or Work and clinical indicators of concussion signs in civilians and military service members.

Repetitive Subconcussive Head Impacts in Sports and Their Impact on Brain Anatomy and Function: A Systematic Review

Repetitive subconcussive head impacts occur regularly in sports. However, the exact relationship between their biomechanical properties and their consequences on brain structure and function has not been clarified yet. We therefore reviewed prospective cohort studies that objectively reported the biomechanical characteristics of repetitive subconcussive head impacts and their impact on brain anatomy and function. Only studies with a pre- to post-measurement design were included. Twenty-four studies met the inclusion criteria. Structural white matter alterations, such as reduced fractional anisotropy and an increase in mean diffusivity values, seem to be evident in athletes exposed to repetitive subconcussive head impacts exceeding 10 g. Such changes are observable after only one season of play. Furthermore, a dose-response relationship exists between white matter abnormalities and the total number of subconcussive head impacts. However, functional changes after repetitive subconcussive head impacts remain inconclusive. We therefore conclude that repetitive subconcussive head impacts induce structural changes, but thus far without overt functional changes.

n-3 PUFA ameliorate functional outcomes following repetitive mTBI in the fat-1 mouse model

Purpose

Repeated mild traumatic brain injuries (mTBI) are a continuing healthcare concern worldwide, given its potential for enduring adverse neurodegenerative conditions. Past research suggests a potential protective effect of n-3 polyunsaturated fatty acids (PUFA) in experimental models of mTBI. The aim of this study was to investigate whether the neuroprotective benefits of n-3 PUFA persist following repetitive weight drop injury (WDI).

Methods

Male fat-1 mice (n = 12), able to endogenously convert n-6 PUFA to n-3 PUFA, and their wild type (WT) counterparts (n = 12) were maintained on a 10% w/w safflower diet. At 9-10 weeks of age, both groups received one mild low-impact WDI on the closed cranium daily, for three consecutive days. Following each WDI, time to righting reflex and seeking behaviour were measured. Neurological recovery, cognitive, motor, and neurobehavioural outcomes were assessed using the Neurological Severity Score (NSS) over 7 days (168 h) post-last WDI. Brains were assessed for cerebral microhemorrhages by Prussian blue and cellular damage by glial fibrillary acidic protein (GFAP) staining.

Results

Fat-1 mice exhibited significantly faster righting reflex and seeking behaviour time, and lower mean NSS scores and at all post-WDI time points (p ≤ 0.05) compared to WT mice. Immunohistochemistry showed no significant difference in presence of cerebral microhemorrhage however, fat-1 mice had significantly lower GFAP staining in comparison to WT mice (p ≤ 0.05).

Conclusion

n-3 PUFA is effective in restoring cognitive, motor, and behavioural function after repetitive WDI, which may be mediated through reduced cellular damage of the brain.

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

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

Instrumented Mouthguards in Elite-Level Men's and Women's Rugby Union: The Incidence and Propensity of Head Acceleration Events in Matches

OBJECTIVES

The aim of this study was to examine head acceleration event (HAE) propensity and incidence during elite-level men's and women's rugby union matches.

METHODS

Instrumented mouthguards (iMGs) were fitted in 92 male and 72 female players from nine elite-level clubs and three international teams. Data were collected during 406 player matches (239 male, 167 female) using iMGs and video analysis. Incidence was calculated as the number of HAEs per player hour and propensity as the proportion of contact events resulting in an HAE at a range of linear and angular thresholds.

RESULTS

HAE incidence above 10 g was 22.7 and 13.2 per hour in men's forwards and backs and 11.8 and 7.2 per hour in women's forwards and backs, respectively. Propensity varied by contact event, with 35.6% and 35.4% of men's tackles and carries and 23.1% and 19.6% of women's tackles and carries producing HAEs above 1.0 krad/s2. Tackles produced significantly more HAEs than carries, and incidence was greater in forwards compared with backs for both sexes and in men compared with women. Women's forwards were 1.6 times more likely to experience a medium-magnitude HAE from a carry than women's backs. Propensity was similar from tackles and carries, and between positional groups, while significantly higher in men than women. The initial collision stage of the tackle had a higher propensity than other stages.

CONCLUSION

This study quantifies HAE exposures in elite rugby union players using iMGs. Most contact events in rugby union resulted in lower-magnitude HAEs, while higher-magnitude HAEs were comparatively rare. An HAE above 40 g occurred once every 60-100 min in men and 200-300 min in women. Future research on mechanisms for HAEs may inform strategies aimed at reducing HAEs.

Preclinical characterization of macrophage-adhering gadolinium micropatches for MRI contrast after traumatic brain injury in pigs

The choroid plexus (ChP) of the brain plays a central role in orchestrating the recruitment of peripheral leukocytes into the central nervous system (CNS) through the blood-cerebrospinal fluid (BCSF) barrier in pathological conditions, thus offering a unique niche to diagnose CNS disorders. We explored whether magnetic resonance imaging of the ChP could be optimized for mild traumatic brain injury (mTBI). mTBI induces subtle, yet influential, changes in the brain and is currently severely underdiagnosed. We hypothesized that mTBI induces sufficient alterations in the ChP to cause infiltration of circulating leukocytes through the BCSF barrier and developed macrophage-adhering gadolinium [Gd(III)]-loaded anisotropic micropatches (GLAMs), specifically designed to image infiltrating immune cells. GLAMs are hydrogel-based discoidal microparticles that adhere to macrophages without phagocytosis. We present a fabrication process to prepare GLAMs at scale and demonstrate their loading with Gd(III) at high relaxivities, a key indicator of their effectiveness in enhancing image contrast and clarity in medical imaging. In vitro experiments with primary murine and porcine macrophages demonstrated that GLAMs adhere to macrophages also under shear stress and did not affect macrophage viability or functions. Studies in a porcine mTBI model confirmed that intravenously administered macrophage-adhering GLAMs provide a differential signal in the ChP and lateral ventricles at Gd(III) doses 500- to 1000-fold lower than those used in the current clinical standard Gadavist. Under the same mTBI conditions, Gadavist did not offer a differential signal at clinically used doses. Our results suggest that macrophage-adhering GLAMs could facilitate mTBI diagnosis.

Concussion Rehabilitation and the Application of Ten Movement Training Principles

Concussion awareness continues to grow in all aspects of healthcare, including the areas of prevention, acute care, and ongoing rehabilitation. Most of the concussion research to date has focussed on the challenges around screening and diagnosing what can be a complex mix of brain impairments that overlay with additional pre-existing comorbidities. While we expect further progress in concussion diagnosis, progress also continues to be made around proactive rehabilitation, with the emergence of interventions that can enhance the recovery process, maximise function and independence with a return to study, work, and play. Traditionally, optimal multimodal assessments of concussion have treated the physical, cognitive, and psychological domains of brain injury separately, which supports diagnosis, and informs appropriate follow-up care. Due to the complex nature of brain injury, multimodal assessments direct care toward professionals from many different disciplines including medicine, physiotherapy, psychology, neuropsychology, ophthalmology, and exercise physiology. In addition, these professionals may work in different fields such as sports, neurorehabilitation, vestibular, musculoskeletal, community, vocational, and general practice clinical settings. Rehabilitation interventions for concussions employed in practice are also likely to use a blend of theoretical principles from motor control, cognitive, and psychological sciences. This scale of diversity can make information dissemination, collaboration, and innovation challenging. The Ten Movement Training Principles (MTPs) have been proposed as a usable and relevant concept to guide and support clinical reasoning in neurorehabilitation. When applied to concussion rehabilitation, these same 10 principles provide a comprehensive overview of key rehabilitation strategies for current and future practice. Future collaborations can use these training principles to support clinical and research innovations including the rapid rise of technologies in this growing field of rehabilitation practice.

An Instrumented Mouthguard for Real-Time Measurement of Head Kinematics under a Large Range of Sport Specific Accelerations

BACKGROUND

Head impacts in sports can produce brain injuries. The accurate quantification of head kinematics through instrumented mouthguards (iMG) can help identify underlying brain motion during injurious impacts. The aim of the current study is to assess the validity of an iMG across a large range of linear and rotational accelerations to allow for on-field head impact monitoring.

METHODS

Drop tests of an instrumented helmeted anthropometric testing device (ATD) were performed across a range of impact magnitudes and locations, with iMG measures collected concurrently. ATD and iMG kinematics were also fed forward to high-fidelity brain models to predict maximal principal strain.

RESULTS

The impacts produced a wide range of head kinematics (16-171 g, 1330-10,164 rad/s2 and 11.3-41.5 rad/s) and durations (6-18 ms), representing impacts in rugby and boxing. Comparison of the peak values across ATD and iMG indicated high levels of agreement, with a total concordance correlation coefficient of 0.97 for peak impact kinematics and 0.97 for predicted brain strain. We also found good agreement between iMG and ATD measured time-series kinematic data, with the highest normalized root mean squared error for rotational velocity (5.47 ± 2.61%) and the lowest for rotational acceleration (1.24 ± 0.86%). Our results confirm that the iMG can reliably measure laboratory-based head kinematics under a large range of accelerations and is suitable for future on-field validity assessments.

The biomechanical signature of loss of consciousness: computational modelling of elite athlete head injuries

Sports related head injuries can cause transient neurological events including loss of consciousness and dystonic posturing. However, it is unknown why head impacts that appear similar produce distinct neurological effects. The biomechanical effect of impacts can be estimated using computational models of strain within the brain. Here, we investigate the strain and strain rates produced by professional American football impacts that led to loss of consciousness, posturing or no neurological signs. We reviewed 1280 National Football League American football games and selected cases where the team's medical personnel made a diagnosis of concussion. Videos were then analysed for signs of neurological events. We identified 20 head impacts that showed clear video signs of loss of consciousness and 21 showing clear abnormal posturing. Forty-one control impacts were selected where there was no observable evidence of neurological signs, resulting in 82 videos of impacts for analysis. Video analysis was used to guide physical reconstructions of these impacts, allowing us to estimate the impact kinematics. These were then used as input to a detailed 3D high-fidelity finite element model of brain injury biomechanics to estimate strain and strain rate within the brain. We tested the hypotheses that impacts producing loss of consciousness would be associated with the highest biomechanical forces, that loss of consciousness would be associated with high forces in brainstem nuclei involved in arousal and that dystonic posturing would be associated with high forces in motor regions. Impacts leading to loss of consciousness compared to controls produced higher head acceleration (linear acceleration; 81.5 g ± 39.8 versus 47.9 ± 21.4; P = 0.004, rotational acceleration; 5.9 krad/s2 ± 2.4 versus 3.5 ± 1.6; P < 0.001) and in voxel-wise analysis produced larger brain deformation in many brain regions, including parts of the brainstem and cerebellum. Dystonic posturing was also associated with higher deformation compared to controls, with brain deformation observed in cortical regions that included the motor cortex. Loss of consciousness was specifically associated with higher strain rates in brainstem regions implicated in maintenance of consciousness, including following correction for the overall severity of impact. These included brainstem nuclei including the locus coeruleus, dorsal raphé and parabrachial complex. The results show that in head impacts producing loss of consciousness, brain deformation is disproportionately seen in brainstem regions containing nuclei involved in arousal, suggesting that head impacts produce loss of consciousness through a biomechanical effect on key brainstem nuclei involved in the maintenance of consciousness.

Cranial Bone Changes Induced by Mild Traumatic Brain Injuries: A Neglected Player in Concussion Outcomes?

Mild traumatic brain injuries (TBIs), particularly when repetitive in nature, are increasingly recognized to have a range of significant negative implications for brain health. Much of the ongoing research in the field is focused on the neurological consequences of these injuries and the relationship between TBIs and long-term neurodegenerative conditions such as chronic traumatic encephalopathy and Alzheimer's disease. However, our understanding of the complex relationship between applied mechanical force at impact, brain pathophysiology, and neurological function remains incomplete. Past research has shown that mild TBIs, even below the threshold that results in cranial fracture, induce changes in cranial bone structure and morphology. These structural and physiological changes likely have implications for the transmission of mechanical force into the underlying brain parenchyma. Here, we review this evidence in the context of the current understanding of bone mechanosensitivity and the consequences of TBIs or concussions. We postulate that heterogeneity of the calvarium, including differing bone thickness attributable to past impacts, age, or individual variability, may be a modulator of outcomes after subsequent TBIs. We advocate for greater consideration of cranial responses to TBI in both experimental and computer modeling of impact biomechanics, and raise the hypothesis that calvarial bone thickness represents a novel biomarker of brain injury vulnerability post-TBI.

The Most Cited and Influential Publications Relating to Ice Hockey Since 2000 Focus Primarily on Concussion and Traumatic Brain Injuries

Purpose

To determine the most frequently cited articles relating to ice hockey since 2000 and conduct a bibliometric analysis of these publications.

Methods

The Clarivate Web of Knowledge database was used to gather data and generate a list of publications relating to "ice hockey" on June 20, 2022. Articles were filtered by the total number of citations accrued and were included or excluded on the basis of relevance to ice hockey; no date of publication, language, or journal restrictions. After the 50 most highly cited articles were identified, articles published before the year 2000 were excluded to avoid bias. The information analyzed from each article included author name (first and last), publication year, country of origin, institutional affiliation (of the first and last author), journal name, research design, main research topic, competition level, and the level of evidence.

Results

Ultimately, 46 studies were included in this analysis. The total number of citations was 8,267 times with an average of 179.7 citations per article. The most cited article was cited 926 times. The articles came from 5 different countries, with the United States and Canada comprising 27 and 13 articles, respectively. All articles were published in English. The American Journal of Sports Medicine published the greatest number of articles. The most studied topic was concussion/traumatic brain injury (n = 26). Professional hockey was the most studied level of competition (n = 15), while college followed (n = 13). Three institutions, University of Calgary, Dartmouth School of Medicine, and University of North Carolina at Chapel Hill were responsible for 32.6% of the top articles (n = 15).

Conclusions

The majority of the most cited articles relating to ice hockey are cohort studies, review articles, and epidemiological studies originating from the United States or Canada. The majority of publications included in the analysis focused on concussion and traumatic brain injury prevalence, identification, diagnosis, outcomes, and prevention, as well as the most studied level of competition was professional, but the greatest number of participants arose from the youth and high school level.

Level of Evidence

Level IV, cross-sectional study.

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

Objectives

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

Design

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

Outcome measures

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

Results

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

Conclusions

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

Do Sports-related Concussions Induce Subsequent Injuries in Elite Male Football Players?

To assess the players' risk of a subsequent injury after sustaining concussive injuries and their return-to-competition in German professional men's football. A prospective injury database in the 1^st Bundesliga was created encompassing 7 seasons (2014/15-2020/21). Cox proportional hazard model analyzed whether a concussive injury increased the risk of a subsequent injury in the first year after the index injury. 6,651 injuries were reported (n=182 concussive injuries). The incidence rate was 0.15 (95% CI 0.13-0.17) per 1000 football hours. A concussive injury was associated with only a slightly numerical higher risk of 7% (HR=1.07, 95% CI 0.78-1.47) in the subsequent year after the injury compared to a randomly selected non-concussive injury, but the effect was not significant. The risk was higher after 6-12 months post-SRC reaching 70% (HR=1.70, 95% CI 1.15-2.52). For 0-3 months (HR=0.76, 95% CI 0.48-1.20) and 3-6 months (HR=0.97, 95% CI 0.62-1.50) the injury risk was lower. The present data do not confirm previously published investigations about an increased injury risk after SRC. Contrasting effects of lower hazard ratios were found early after SRC, followed by an increase after 6-12 months. Further research should look into compliance rates with regards to return-to-competition protocols.

Comparison of Clinical Outcomes Between Athletes With Immediate and Delayed Onset of Symptoms Following Sport-Related Concussion

OBJECTIVE

To compare characteristics and clinical outcomes of adolescent athletes with immediate and delayed onset of symptoms following sport-related concussion (SRC). A secondary objective was to describe the symptoms that are delayed and the timing of symptom onset.

DESIGN

Prospective, repeated measures study.

SETTING

Concussion Specialty Clinic.

PARTICIPANTS

One hundred fifty-two participants (63.3% men) aged 11 to 24 (15.78 ± 3.47) evaluated within 7 days (3.47 ± 1.66) of sustaining an SRC.

INDEPENDENT VARIABLE

Group classification of immediate (IMMEDIATE) or delayed onset of symptoms (DELAYED; >60 seconds following mechanism of injury) through structured clinical interview.

MAIN OUTCOME MEASURES

Group comparisons on demographic and medical history factors, concussion and clinical profile symptom scores, computerized neurocognitive test scores, vestibular/oculomotor screening scores, and days to medical clearance.

RESULTS

24.3% of athletes in the sample were DELAYED. The groups did not differ on demographics and medical history. The DELAYED group had increased likelihood of posttraumatic migraine (PTM) as a primary/secondary clinical profile ( P = 0.03). Groups did not differ on any other clinical profiles ( P > 0.05). Groups did not differ on recovery time ( P = 0.47), the IMMEDIATE group higher dizziness on vestibular/ocular motor screening ( P = 0.016) and increased likelihood of dizziness being the initial symptom experienced ( P < 0 .001).

CONCLUSIONS

The results indicated that delayed onset of symptoms in athletes were relatively common following SRC, supporting continued evaluation of athletes for several days following suspected injuries. Delayed onset of symptoms was associated with PTM, whereas immediate onset was associated with more pronounced vestibular dysfunction, suggesting that clinicians should consider the timing of symptom onset when assessing and treating athletes following SRC.

Concussive Biomechanics in a Women’s Soccer Player: A Validation Clinical Case Report

A concussed 19-year-old female midfielder on an National Collegiate Athletic Association (NCAA) Division III soccer team reported to the athletic training clinic complaining of a headache that began 4 days previously during a game where she headed several long punts. Despite delayed reporting, the patient returned to full participation without complication 13 days after her injury. The biomechanical data for the impacts she received on the day of injury were much lower than those presented in the literature as causing concussion for male athletes. Therefore, impact magnitude should not be used as an indicator for injury, as smaller, seemingly insignificant impacts can cause concussion.

Does Increasing the Severity of Penalties Assessed in Association With the "Zero Tolerance for Head Contact" Policy Translate to a Reduction in Head Impact Rates in Youth Ice Hockey?

OBJECTIVE

The risk of concussion is high in Canadian youth ice hockey. Aiming to reduce this burden, in 2011, Hockey Canada implemented a national "zero tolerance for head contact (HC)" policy mandating the penalization of any player HC. In 2018 to 2020, Hockey Canada further amended this HC policy including stricter enforcement of severe HCs. This study aimed to compare HC rates, head impact location, and HC enforcement prepolicy, postpolicy, and after policy amendments in elite U15 Canadian youth ice hockey.

DESIGN

This is a prospective cohort study.

SETTING

A collection of events with the video camera located at the highest point near center ice in public ice hockey arenas in Calgary, Alberta.

PARTICIPANTS

A convenience sample of 10 AA U15 games prepolicy (2008-2009), 8 games postpolicy (2013-2014), and 10 games after policy amendments (2020-2021).

INDEPENDENT VARIABLES

An analysis of 3 cohort years regarding the HC-policy implementation and amendments.

MAIN OUTCOME MEASURES

Using Dartfish video-analysis software, all player contacts and HCs [direct (HC1), indirect (eg, boards, ice) (HC2)] were tagged using validated criteria. Univariate Poisson regression clustering by team-game offset by game length (minutes) was used to estimate incidence rates (IR) and incidence rate ratios (IRR) between cohorts.

RESULTS

With additional rule modifications, a 30% reduction in HC1s emerged (IRR 2013-2020 = 0.70, 95% CI, 0.51-0.95). Since the HC-policy implementation, HC1s decreased by 24% (IRR 2008-2020 = 0.76, 95% CI, 0.58-0.99). The proportion of HC1s penalized was similar across cohorts (P 2008-2009 = 14.4%; P 2013-2014 = 15.5%; P 2020-2021 = 16.2%).

CONCLUSIONS

The HC-policy amendments have led to decreased HC1 rates. However, referee enforcement can further boost the HC-policy effectiveness. These findings can help future referee training and potential rule modifications to increase player safety nationally.

Evidence to Eliminate Double-Leg Conditions From the Modified Balance Error Scoring System and Balance Error Scoring System

OBJECTIVE

The purpose of our study was to assess the differences between the Balance Error Scoring System (BESS), modified BESS (mBESS), and both measures with the double-leg (DL) stances removed [BESS-revised (BESS-R) and mBESS-revised (mBESS-R)] among healthy and concussed collegiate student-athletes.

DESIGN

Retrospective, repeated-measures cohort study.

SETTING

Clinical.

PATIENTS OR OTHER PARTICIPANTS

Healthy and concussed collegiate athletes (baseline n = 622, postinjury n = 41) from 12 National Collegiate Athletic Association Division I sports cheer and dance at a single university.

INTERVENTION OR INDEPENDENT VARIABLES

Balance Error Scoring System, mBESS, BESS-R, and mBESS-R test versions from baseline and postinjury testing.

MAIN OUTCOME MEASURES

The mBESS and BESS and their revised versions with DL stances removed (mBESS-R and BESS-R) scores were compared at baseline. Baseline and postinjury scores for all 4 BESS variations and the 6 BESS conditions were compared for those who sustained a concussion.

RESULTS

The BESS and BESS-R were statistically different at baseline for the entire sample (99.6% confidence interval 0.32, 0.38, P > 0.0001). None of the other comparisons were significantly different ( P > 0.004).

CONCLUSION

Although our results do suggest statistically significant differences between the BESS and BESS-R test versions, they do not represent clinically meaningful differences. The greatest mean difference between all test versions was <1 error; therefore, these BESS versions may not be specific enough to identify balance deficits at baseline or postinjury. Elimination of the time intensive DL measures in the revised BESS variations may be a more clinically practical alternative.

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

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

A non-invasive biomechanical model of mild TBI in larval zebrafish

A mild traumatic brain injury is a neurological dysfunction caused by biomechanical forces transmitted to the brain in physical impacts. The current understanding of the neuropathological cascade resulting in the manifested clinical signs and symptoms is limited due to the absence of sensitive brain imaging methods. Zebrafish are established models for the reproduction and study of neurobiological pathologies. However, all available models mostly recreate moderate-to-severe focal injuries in adult zebrafish. The present work has induced a mild brain trauma in larval zebrafish through a non-invasive biomechanical approach. A custom-made apparatus with a commercially available motor was employed to expose larvae to rapidly decelerating linear movements. The neurophysiological changes following concussion were assessed through behavioural quantifications of startle reflex locomotor distance and habituation metrics. Here we show that the injury was followed, within five minutes, by a transient anxiety state and CNS dysfunction manifested by increased startle responsivity with impaired startle habituation, putatively mirroring the human clinical sign of hypersensitivity to noise. Within a day after the injury, chronic effects arose, as evidenced by an overall reduced responsivity to sensory stimulation (lower amplitude and distance travelled along successive stimuli), reflecting the human post-concussive symptomatology. This study represents a step forward towards the establishment of a parsimonious (simple, less ethically concerning, yet sensitive) animal model of mild TBI. Our behavioural findings mimic aspects of acute and chronic effects of human concussion, which warrant further study at molecular, cellular and circuit levels. While our model opens wide avenues for studying the underlying cellular and molecular pathomechanisms, it also enables high-throughput testing of therapeutic interventions to accelerate post-concussive recovery.

Head Impact Exposure in Youth and Collegiate American Football

The relationship between head impact and subsequent brain injury for American football players is not well-defined, especially for youth. The objective of this study is to quantify and assess Head Impact Exposure (HIE) metrics among youth and collegiate football players. This multi-season study enrolled 639 unique athletes (354 collegiate; 285 youth, ages 9-14), recording 476,209 head impacts (367,337 collegiate; 108,872 youth) over 971 sessions (480 collegiate; 491 youth). Youth players experienced 43 and 65% fewer impacts per competition and practice, respectively, and lower impact magnitudes compared to collegiate players (95th percentile peak linear acceleration (PLA, g) competition: 45.6 vs 61.9; 95th percentile PLA practice: 42.6 vs 58.8; 95th percentile peak rotational acceleration (PRA, rad·s^-2) competition: 2262 vs 4422; 95th percentile PRA practice: 2081 vs 4052; 95th percentile HITsp competition: 25.4 vs 32.8; 95th percentile HITsp practice: 23.9 vs 30.2). Impacts during competition were more frequent and of greater magnitude than during practice at both levels. Quantified comparisons of head impact frequency and magnitude between youth and collegiate athletes reveal HIE differences as a function of age, and expanded insight better informs the development of age-appropriate guidelines for helmet design, prevention measures, standardized testing, brain injury diagnosis, and recovery management.

‘Falling heads’: investigating reflexive responses to head–neck perturbations

Background

Reflexive responses to head–neck perturbations affect the injury risk in many different situations ranging from sports-related impact to car accident scenarios. Although several experiments have been conducted to investigate these head–neck responses to various perturbations, it is still unclear why and how individuals react differently and what the implications of these different responses across subjects on the potential injuries might be. Therefore, we see a need for both experimental data and biophysically valid computational Human Body Models with bio-inspired muscle control strategies to understand individual reflex responses better.

Methods

To address this issue, we conducted perturbation experiments of the head–neck complex and used this data to examine control strategies in a simulation model. In the experiments, which we call ’falling heads’ experiments, volunteers were placed in a supine and a prone position on a table with an additional trapdoor supporting the head. This trapdoor was suddenly released, leading to a free-fall movement of the head until reflexive responses of muscles stopped the downwards movement.

Results

We analysed the kinematic, neuronal and dynamic responses for all individuals and show their differences for separate age and sex groups. We show that these results can be used to validate two simple reflex controllers which are able to predict human biophysical movement and modulate the response necessary to represent a large variability of participants.

Conclusions

We present characteristic parameters such as joint stiffness, peak accelerations and latency times. Based on this data, we show that there is a large difference in the individual reflexive responses between participants. Furthermore, we show that the perturbation direction (supine vs. prone) significantly influences the measured kinematic quantities. Finally, ’falling heads’ experiments data are provided open-source to be used as a benchmark test to compare different muscle control strategies and to validate existing active Human Body Models directly.

Career Head Impact Exposure Profile of Canadian University Football Players

This study quantified head impact exposures for Canadian university football players over their varsity career. Participants included 63 players from one team that participated in a minimum of 3 seasons between 2013 and 2018. A total of 127,192 head impacts were recorded from 258 practices and 65 games. The mean (SD) number of career impacts across all positions was 2023.1 (1296.4), with an average of 37.1 (20.3) impacts per game and 7.4 (4.4) impacts per practice. The number of head impacts that players experienced during their careers increased proportionally to the number of athletic exposures (P < .001, r = .57). Linebackers and defensive and offensive linemen experienced significantly more head impacts than defensive backs, quarterbacks, and wide receivers (P ≤ .014). Seniority did not significantly affect the number of head impacts a player experienced. Mean linear acceleration increased with years of seniority within defensive backs and offensive linemen (P ≤ .01). Rotational velocity increased with years of seniority within defensive backs, defensive and offensive linemen, running backs, and wide receivers (P < .05). These data characterize career metrics of head impact exposure for Canadian university football players and provide insights to reduce head impacts through rule modifications and contact regulations.

Quantification of Head Acceleration Events in Rugby League: An Instrumented Mouthguard and Video Analysis Pilot Study

Instrumented mouthguards (iMG) were used to collect head acceleration events (HAE) in men's professional rugby league matches. Peak linear acceleration (PLA), peak angular acceleration (PAA) and peak change in angular velocity (ΔPAV) were collected using custom-fit iMG set with a 5 g single iMG-axis recording threshold. iMG were fitted to ten male Super League players for thirty-one player matches. Video analysis was conducted on HAE to identify the contact event; impacted player; tackle stage and head loading type. A total of 1622 video-verified HAE were recorded. Approximately three-quarters of HAE (75.7%) occurred below 10 g. Most (98.2%) HAE occurred during tackles (59.3% to tackler; 40.7% to ball carrier) and the initial collision stage of the tackle (43.9%). The initial collision stage resulted in significantly greater PAA and ΔPAV than secondary contact and play the ball tackle stages (p < 0.001). Indirect HAE accounted for 29.8% of HAE and resulted in significantly greater ΔPAV (p < 0.001) than direct HAE, but significantly lower PLA (p < 0.001). Almost all HAE were sustained in the tackle, with the majority occurring during the initial collision stage, making it an area of focus for the development of player protection strategies for both ball carriers and tacklers. League-wide and community-level implementation of iMG could enable a greater understanding of head acceleration exposure between playing positions, cohorts, and levels of play.

Head Impact Exposure of a Youth Football Team over Eight Consecutive Seasons

PURPOSE

This study examined HIE of middle school football players over multiple seasons.

METHODS

Head impact exposure was evaluated in 103 football players (11-14 yr) who participated in a community-based youth tackle football program, up to 2 yr, with the same coaching staff over eight consecutive seasons (2012-2019). Head impact exposure was assessed using the Head Impact Telemetry System. Median of individual mean head impacts per session (HIPS) and median of individual 50th and 95th percentile head impact magnitudes were compared across seasons.

RESULTS

There were 33,519 head impacts measured throughout the study. Median HIPS for all sessions decreased every year, with a significant reduction from 2012 to 2019 (11.1 vs 2.3 HIPS; P < 0.05). Median game HIPS were significantly reduced in 2019 compared with 2012-14 (5.00 vs 16.30-17.75 HIPS; P < 0.05). Median practice HIPS were reduced by 81.3%, whereas median game HIPS were reduced by 69.3%. Median 50th and 95th percentile linear and rotational acceleration were lower in 2019 compared with some earlier years but remained unchanged during games.

CONCLUSIONS

Head impacts incurred by youth football players decreased substantially over eight seasons, with players in the final year sustaining approximately one fifth the HIPS as players experienced during the first year. The most prominent decline occurred in practices, although players also had much fewer head impacts in games. These results suggest that coaches' and/or players' behavior can be modified to greatly reduce the head impact burden in youth football.

Quantifying head impacts and neurocognitive performance in collegiate boxers

Head impacts and neurocognition were quantified in 27 intercollegiate male boxers engaged in two, two-minute sparring rounds. Head impacts were measured using Instrumented Boxing Headgear (IBH). Pre and post-sparring neurocognitive performance was compared using two computerized neuropsychological test batteries (CNTs): Immediate Post-concussion Assessment and Cognitive Testing (ImPACT™) and Automated Neuropsychological Assessment Metrics - Military Battery (ANAM4® MIL). An average of 27.63 ± 17.87 impacts above the 9.6 g IBH threshold were recorded per boxer, with average peak linear acceleration of 23.48 ± 15.20 g and average peak rotational acceleration of 1761.40 ± 1064.34 rad/s². Small, but measurable declines in delayed memory and improvement in response time from pre- to post-bout were noted. Number of impacts and concussion history predicted degraded memory performance. This is a runique quantificationof head impacts in collegiate boxing, which were similar in frequency and location, but lower in magnitude as compared to amateur boxing. Improved understanding of impact kinematics may enhance safety in boxing and other contact sports. Subtle post-bout decrements in delayed memory performance and mild improvement in response time reinforce prior research and provide evidence of congruence in our two CNT assessments, which may facilitate comparisons of outcomes across settings utilizing these tests.

Head Games: A Systematic Review and Meta-analysis Examining Concussion and Head Impact Incidence Rates, Modifiable Risk Factors, and Prevention Strategies in Youth Tackle Football

OBJECTIVES

The aims were to (1) examine the rates and mechanisms of concussion and head impact in youth football (high school level or younger); (2) identify modifiable risk factors for concussion and head impact; and (3) evaluate the effectiveness of prevention strategies in tackle football at any level.

METHODS

Nine databases (CINAHL Plus with Full Text; Cochrane Central Register of Controlled Trials; EMBASE; ERIC; Ovid MEDLINE(R) and Epub Ahead of Print, In-Process & Other Non-Indexed Citations and Daily; ProQuest Dissertations & Theses Global Database; PsycINFO; Scopus; and SPORTDiscus with Full Text) were searched using the search strategy focusing on four main concepts: concussion/head impact, tackle football, modifiable risk factors, and primary prevention. Two reviewers completed title, abstract, and full-text screening as well as risk of bias assessment (using the Downs and Black checklist), with a third author available to resolve any disagreements.

MAIN RESULTS

After removing duplicates, 1911 articles were returned. Fifty-eight articles were included in the review and 20 in the meta-analysis. The overall combined rates of concussion (including game and practice-related concussion) based on the meta-analysis were 0.78 concussions/1000 athlete exposures [95% confidence interval (CI) 0.67-0.89] for high school football (ages 13-19) and 1.15 concussions/1000 athlete exposures (95% CI 0.89-1.41) for minor football players (ages 5-15). There is evidence that contact training and practice contact restrictions have reduced the rate of head impacts and concussion. Heads Up Football (an intervention focused on coach education and contact training) has been shown to reduce the rate of concussion by 32% and head impacts by 38% amongst high school football players. Limiting contact practices in high schools to 2 days per week reduced practice head impacts per player-season by 42%, and limiting full contact in practice to 75 min per week in the second week of the season and 60 min in week 3 and beyond resulted in a 54% decrease in the practice-related concussion rate (p = 0.003).

CONCLUSIONS

This review identified a critical need for interventions to address the high rates of concussion and head impact in youth football. To date, contact training and contact restrictions have the strongest evidence supporting their effectiveness at reducing these rates. Future research should use consistent concussion definitions and validated injury surveillance systems, and ensure complete reporting of participant characteristics and sampling details. Prospero ID CRD42020193775.

Head Impact Sensor Triggering Bias Introduced by Linear Acceleration Thresholding

Contact sports players frequently sustain head impacts, most of which are mild impacts exhibiting 10-30 g peak head center-of-gravity (CG) linear acceleration. Wearable head impact sensors are commonly used to measure exposure and typically detect impacts using a linear acceleration threshold. However, linear acceleration across the head can substantially vary during 6-degree-of-freedom motion, leading to triggering biases that depend on sensor location and impact condition. We conducted an analytical investigation with impact characteristics extracted from on-field American football and soccer data. We assumed typical mouthguard sensor locations and evaluated whether simulated multi-directional impacts would trigger recording based on per-axis or resultant acceleration thresholding. Across 1387 impact directions, a 10g peak CG linear acceleration impact would trigger at only 24.7% and 31.8% of directions based on a 10 g per-axis and resultant acceleration threshold, respectively. Anterior impact locations had lower trigger rates and even a 30 g impact would not trigger recording in some directions. Such triggering biases also varied by sensor location and linear-rotational head kinematics coupling. Our results show that linear acceleration-based impact triggering could lead to considerable bias in head impact exposure measurements. We propose a set of recommendations to consider for sensor manufacturers and researchers to mitigate this potential exposure measurement bias.

Head Impact Research Using Inertial Sensors in Sport: A Systematic Review of Methods, Demographics, and Factors Contributing to Exposure

BACKGROUND

The number and magnitude of head impacts have been assessed in-vivo using inertial sensors to characterise the exposure in various sports and to help understand their potential relationship to concussion.

OBJECTIVES

We aimed to provide a comprehensive review of the field of in-vivo sensor acceleration event research in sports via the summary of data collection and processing methods, population demographics and factors contributing to an athlete's exposure to sensor acceleration events.

METHODS

The systematic search resulted in 185 cohort or cross-sectional studies that recorded sensor acceleration events in-vivo during sport participation.

RESULTS

Approximately 5800 participants were studied in 20 sports using 18 devices that included instrumented helmets, headbands, skin patches, mouthguards and earplugs. Female and youth participants were under-represented and ambiguous results were reported for these populations. The number and magnitude of sensor acceleration events were affected by a variety of contributing factors, suggesting sport-specific analyses are needed. For collision sports, being male, being older, and playing in a game (as opposed to a practice), all contributed to being exposed to more sensor acceleration events.

DISCUSSION

Several issues were identified across the various sensor technologies, and efforts should focus on harmonising research methods and improving the accuracy of kinematic measurements and impact classification. While the research is more mature for high-school and collegiate male American football players, it is still in its early stages in many other sports and for female and youth populations. The information reported in the summarised work has improved our understanding of the exposure to sport-related head impacts and has enabled the development of prevention strategies, such as rule changes.

CONCLUSIONS

Head impact research can help improve our understanding of the acute and chronic effects of head impacts on neurological impairments and brain injury. The field is still growing in many sports, but technological improvements and standardisation of processes are needed.

Potential Mechanisms of Acute Standing Balance Deficits After Concussions and Subconcussive Head Impacts: A Review

Standing balance deficits are prevalent after concussions and have also been reported after subconcussive head impacts. However, the mechanisms underlying such deficits are not fully understood. The objective of this review is to consolidate evidence linking head impact biomechanics to standing balance deficits. Mechanical energy transferred to the head during impacts may deform neural and sensory components involved in the control of standing balance. From our review of acute balance-related changes, concussions frequently resulted in increased magnitude but reduced complexity of postural sway, while subconcussive studies showed inconsistent outcomes. Although vestibular and visual symptoms are common, potential injury to these sensors and their neural pathways are often neglected in biomechanics analyses. While current evidence implies a link between tissue deformations in deep brain regions including the brainstem and common post-concussion balance-related deficits, this link has not been adequately investigated. Key limitations in current studies include inadequate balance sampling duration, varying test time points, and lack of head impact biomechanics measurements. Future investigations should also employ targeted quantitative methods to probe the sensorimotor and neural components underlying balance control. A deeper understanding of the specific injury mechanisms will inform diagnosis and management of balance deficits after concussions and subconcussive head impact exposure.

Characteristics of potential concussive events in elite male gaelic football players: A descriptive video-analysis

Gaelic football (GF) is a high-impact sport and Sport-Related Concussion (SRC) is an issue within the game. Our aim was to evaluate the characteristics of Potential Concussive Events (PCEs) that occur in the Gaelic Athletic Association National Football League and extrapolate this data to reduce the incidence and severity of SRC. PCEs may or may not lead to a clinical diagnosis of SRC, but represent high-risk events and therefore may be a useful indicator. A video-analysis approach was undertaken to identify PCEs throughout two seasons of play using broadcast footage, and characteristics of each PCE were measured based on previously validated methods. A total of 242 PCEs were identified over 111 matches (2.18 per match, 58.14 per 1000 hours of exposure). PCEs were frequently not anticipated by the player (40.5%, n = 98). The most common impact locations were the mandibular region (33.1%, n = 80) and the temporal region (21.1%, n = 51), and the most frequently observed mechanism was hand/fist to head (27.3%, n = 66). A second-hit was observed in 34 PCEs (14.0%). The findings provide initial guidance for the development of player protection strategies to reduce the incidence and severity of SRC in Gaelic Football.

Immunoglobulin A Autoreactivity toward Brain Enriched and Apoptosis-Regulating Proteins in Saliva of Athletes after Acute Concussion and Subconcussive Impacts

The diagnosis and management of concussion is hindered by its diverse clinical presentation and assessment tools reliant on subjectively experienced symptoms. The biomechanical threshold of concussion is also not well understood, and asymptomatic concussion or "subconcussive impacts" of variable magnitudes are common in contact sports. Concerns have risen because athletes returning to activity too soon have an increased risk of prolonged recovery or long-term adverse health consequences. To date, little is understood on a molecular level regarding concussion and subconcussive impacts. Recent research suggests that neuroinflammatory mechanisms may serve an important role subsequent to concussion and possibly to subconcussive impacts. These studies suggest that autoantibodies may be a valuable tool for detection of acute concussion and monitoring for changes caused by cumulative exposure to subconcussive impacts. Hence, we aimed to profile the immunoglobulin (Ig)A autoantibody repertoire in saliva by screening a unique sport-related head trauma biobank. Saliva samples (n = 167) were donated by male and female participants enrolled in either the concussion (24-48 h post-injury) or subconcussion (non-concussed participants having moderate or high cumulative subconcussive impact exposure) cohorts. Study design included discovery and verification phases. Discovery aimed to identify new candidate autoimmune targets of IgA. Verification tested whether concussion and subconcussion cohorts increased IgA reactivity and whether cohorts showed similarities. The results show a significant increase in the prevalence of IgA toward protein fragments representing 5-hydroxytryptamine receptor 1A (HTR1A), serine/arginine repetitive matrix 4 (SRRM4) and FAS (tumor necrosis factor receptor superfamily member 6) after concussion and subconcussion. These results may suggest that concussion and subconcussion induce similar physiological effects, especially in terms of immune response. Our study demonstrates that saliva is a potential biofluid for autoantibody detection in concussion and subconcussion. After rigorous confirmation in much larger independent study sets, a validated salivary autoantibody assay could provide a non-subjective quantitative means of assessing concussive and subconcussive events.

The relation between neck strength and psychological distress: preliminary evidence from collegiate soccer athletes

AIM

To examine whether neck strength and symmetry are associated with psychological function in athletes with exposure to repetitive head impacts.

METHODS

Collegiate soccer (n = 29) and limited/noncontact (n = 63) athletes without a history of concussion completed the Brief Symptom Inventory 18 and assessments of isometric neck strength. Neck strength symmetry was calculated as the difference in strength between opposing muscle groups.

RESULTS

The results demonstrated that lower neck strength was associated with more symptoms of anxiety, whereas asymmetry in neck strength was associated with more symptoms of somatization and depression in soccer athletes only.

CONCLUSION

These preliminary results suggest that greater neck strength/symmetry is related to better psychological function in athletes who have higher exposure to repetitive head impacts.

Postural Control Deficits After Repetitive Soccer Heading

OBJECTIVE

To determine the acute effects of repetitive soccer heading on postural control.

DESIGN

Prospective study; participants were divided into 2 groups: a soccer heading group and a control group.

SETTING

Biomechanics laboratory.

PARTICIPANTS

One hundred sixty participants, including youth (age = 13.0 ± 0.8 years), high school (age = 17.2 ± 1.0 years), and collegiate (age = 20.2 ± 1.3 years) male and female soccer players, participated in this study.

INTERVENTIONS

Participants in the soccer heading group performed 12 soccer headers (initial velocity = 11.2 m/s). Postural control testing was performed both before (PRE) and immediately after (POST) the purposeful soccer headers. Control participants performed postural control testing PRE and POST a 15-minute wait period. During postural control testing, participants were asked to stand on the MobileMat (Tekscan Inc, Boston, Massachusetts) for two 2-minute intervals with their hands on their hips and their feet together with one eyes-open and one eyes-closed trial.

MAIN OUTCOME MEASURES

Using the center-of-pressure data, 95% area, sway velocity, and ApEn were calculated. Multilevel linear models were used to analyze the effects of age, sex, group, condition, and concussion history simultaneously.

RESULTS

Participants in the soccer heading group had significantly higher sway velocity POST than participants in the control group after controlling for age, sex, concussion history, condition, and PRE (t = -3.002; P = 0.003; 95% confidence interval, -0.482 to -0.100). There were no significant differences from PRE to POST for 95% area, M/L ApEn, and A/P ApEn.

CONCLUSIONS

Repetitive soccer heading does not affect most postural control measures, even among youth athletes. However, sway velocity increased after heading relative to control participants independent of age, sex, and concussion history.

A new open-access platform for measuring and sharing mTBI data

Despite numerous research efforts, the precise mechanisms of concussion have yet to be fully uncovered. Clinical studies on high-risk populations, such as contact sports athletes, have become more common and give insight on the link between impact severity and brain injury risk through the use of wearable sensors and neurological testing. However, as the number of institutions operating these studies grows, there is a growing need for a platform to share these data to facilitate our understanding of concussion mechanisms and aid in the development of suitable diagnostic tools. To that end, this paper puts forth two contributions: (1) a centralized, open-access platform for storing and sharing head impact data, in collaboration with the Federal Interagency Traumatic Brain Injury Research informatics system (FITBIR), and (2) a deep learning impact detection algorithm (MiGNet) to differentiate between true head impacts and false positives for the previously biomechanically validated instrumented mouthguard sensor (MiG2.0), all of which easily interfaces with FITBIR. We report 96% accuracy using MiGNet, based on a neural network model, improving on previous work based on Support Vector Machines achieving 91% accuracy, on an out of sample dataset of high school and collegiate football head impacts. The integrated MiG2.0 and FITBIR system serve as a collaborative research tool to be disseminated across multiple institutions towards creating a standardized dataset for furthering the knowledge of concussion biomechanics.

Head impact forces in blind football are greater in competition than training and increased cervical strength may reduce impact magnitude

Paralympic Blind Association Football has the highest rate of injury of any Paralympic sport and head injuries are common. This study aims to quantify head impact incidence and magnitude in Blind Football, and to examine contributing factors. This Observational study based on a Blind Football Team comprising seven male athletes 28.63 years (SD 9.74, range 16-46) over 6 months. Head mounted impact sensors were used to measure the frequency and location of impacts, as well as their linear acceleration and rotational velocity. Cervical isometric strength and proprioception was measured. There were 374 impacts recorded in 212.5 athlete hours. There was a higher rate of impacts in matches than training (Incidence Risk Ratio 2.58, 95% CI 2.01-3.30). Greater cervical strength was associated with reduced linear acceleration of impacts (R² = 0.1912, p = .020). Blind Football players are exposed to a greater number of head impacts in matches than training. Neck muscle strength may influence magnitude of head impact forces in this sport but further study is required to further investigate.

Incidence of Head Contacts, Penalties, and Player Contact Behaviors in Youth Ice Hockey: Evaluating the “Zero Tolerance for Head Contact” Policy Change

Background:

To reduce the risk of concussion in youth ice hockey, Hockey Canada implemented a national “zero tolerance for head contact” (HC) policy in 2011. A previous cohort study revealed higher concussion rates after this implementation in players aged 11 to 14 years. However, it is unknown whether the elevated risk was due to higher HC rates or factors such as increased concussion awareness and reporting.

Purpose:

To compare the rates of primary and secondary HCs and HC policy enforcement in elite U15 ice hockey leagues (players <15 years) before (2008-2009) and after (2013-2014) the zero-tolerance policy change.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

A total of 32 elite U15 games before (n_2008-2009 = 16; 510 players) and after (n_2013-2014 = 16; 486 players) HC policy implementation were video recorded. Videos were analyzed with validated criteria for identifying HC types (primary/direct contact by players [HC1], secondary/indirect contact via boards, glass, or ice surface [HC2]) and other player-to-player contact behavior. Referee-assessed penalties were cross-referenced with the official Hockey Canada casebook, and penalty types were displayed using proportions. Univariate Poisson regression (adjusted for cluster by team game, offset by game length [minutes]) was used to estimate HC incidence rates (IRs) and incidence rate ratios (IRRs) between cohorts.

Results:

A total of 506 HCs were analyzed, 261 before HC policy implementation (IR, 16.6/100 team minutes) and 245 after implementation (IR, 15.5/100 team minutes). The HC1 rate (IRR, 1.05; 95% CI, 0.86-1.28) and HC2 rate (IRR, 0.74; 95% CI, 0.50-1.11) did not significantly differ before versus after implementation. Only 12.0% and 13.6% of HC1s were penalized pre- and postimplementation, respectively. Before implementation, HC1s were commonly penalized as roughing or elbowing penalties (59%), while after implementation, HC1s were penalized with the HC penalty (76%), and only 8% as roughing or elbowing.

Conclusion:

Despite implementation of the “zero tolerance for HC” policy, there was no difference in the rate of HC1s and HC2s or the proportion of HC1 penalized from before to after implementation. This research is instrumental in informing Hockey Canada’s future referee training and rule enforcement modifications.

Subtypes of Sport-Related Concussion: a Systematic Review and Meta-cluster Analysis

Objective

Current clinical guidelines provide a unitary approach to manage sport-related concussion (SRC), while heterogeneity in the presentation of symptoms suggests that subtypes of SRC may exist. We systematically reviewed the available evidence on SRC subtypes and associated clinical outcomes.

Data Sources

Ovid Medline, Embase, PsycINFO, and SPORTDiscus

Eligibility Criteria for Selecting Studies

Electronic databases were searched for studies: (i) identifying SRC symptom clusters using classification methodology; or (ii) associating symptom clusters to clinical outcome variables. A total of 6,146 unique studies were identified, of which 75 full texts were independently assessed by two authors for eligibility. A total of 22 articles were included for systematic review.

Data Extraction

Two independent authors performed data extraction and risk of bias analysis using the Cochrane Collaboration tool.

Data Synthesis

Six studies found evidence for existence of SRC symptom clusters. Combining the available literature through Multiple Correspondence Analysis (MCA) provided evidence for the existence of a migraine cluster, a cognitive–emotional cluster, a sleep–emotional cluster, a neurological cluster, and an undefined feelings cluster. Nineteen studies found meaningful associations between SRC symptom clusters and clinical outcomes. Clusters mapping to the migraine cluster were most frequently reported in the literature and were most strongly related to aspects of clinical outcome.

Conclusions

The available literature provides evidence for the existence of at least five subtypes in SRC symptomatology, with clear relevance to clinical outcome. Systematically embedding the differentiation of SRC subtypes into prognosis, clinical management, and intervention strategies may optimize the recovery from SRC.

Electronic supplementary material

The online version of this article (10.1007/s40279-020-01321-9) contains supplementary material, which is available to authorized users.

Relating on-field youth football head impacts to pneumatic ram laboratory testing procedures

A youth-specific football helmet testing standard has been proposed to address the physical and biomechanical differences between adult and youth football players. This study sought to relate the proposed youth standard-defined laboratory impacts to on-field head impacts collected from youth football players. Head impact data from 112 youth football players (ages 9-14) were collected through the use of helmet-mounted accelerometer arrays. These head impacts were filtered to only include those that resided in corridors near prescribed National Operating Committee on Standards for Athletic Equipment (NOCSAE) impact locations. Peak linear head acceleration and peak rotational head acceleration magnitudes collected from pneumatic ram impactor tests as specified by the proposed NOCSAE youth standard were compared to the distribution of on-field head impacts. All laboratory impact tests were among the top 10% in terms of magnitude for Severity Index and peak rotational acceleration of matched location head impacts experienced by youth football players. As concussive head impacts are among the most severe impacts experienced on the field, a safety standard geared toward mitigating concussion should assess the most severe on-field head impacts. This proposed testing standard may be refined as more becomes known regarding the biomechanics of concussion among youth athletes.

Network Analysis of Sport-Related Concussion Research During the Past Decade (2010-2019)

CONTEXT

Research into sport-related concussion (SRC) has grown substantially over the past decade, yet no authors to date have synthesized developments over this critical time period.

OBJECTIVE

To apply a network-analysis approach in evaluating trends in the SRC literature using a comprehensive search of original, peer-reviewed research articles involving human participants published between January 1, 2010, and December 15, 2019.

DESIGN

Narrative review.

MAIN OUTCOME MEASURE(S)

Bibliometric maps were derived from a comprehensive search of all published, peer-reviewed SRC articles in the Web of Science database. A clustering algorithm was used to evaluate associations among journals, organizations or institutions, authors, and key words. The online search yielded 6130 articles, 528 journals, 7598 authors, 1966 organizations, and 3293 key words.

RESULTS

The analysis supported 5 thematic clusters of journals: (1) biomechanics/sports medicine (n = 15), (2) pediatrics/rehabilitation (n = 15), (3) neurotrauma/neurology/neurosurgery (n = 11), (4) general sports medicine (n = 11), and (5) neuropsychology (n = 7). The analysis identified 4 organizational clusters of hub institutions: (1) University of North Carolina (n = 19), (2) University of Toronto (n = 19), (3) University of Michigan (n = 11), and (4) University of Pittsburgh (n = 10). Network analysis revealed 8 clusters for SRC key words, each with a central topic area: (1) epidemiology (n = 14), (2) rehabilitation (n = 12), (3) biomechanics (n = 11), (4) imaging (n = 10), (5) assessment (n = 9), (6) mental health/chronic traumatic encephalopathy (n = 9), (7) neurocognition (n = 8), and (8) symptoms/impairments (n = 5).

CONCLUSIONS

The findings suggest that during the past decade SRC research has (1) been published primarily in sports medicine, pediatric, and neuro-focused journals, (2) involved a select group of researchers from several key institutions, and (3) concentrated on new topical areas, including treatment or rehabilitation and mental health.

The Effects of Headgear in High School Girls' Lacrosse

Background:

Girls’ lacrosse headgear that met the ASTM International performance standard (ASTM F3137) became available in 2017. However, the effects of headgear use on impact forces during game play are unknown.

Purpose:

To evaluate potential differences in rates, magnitudes, and game-play characteristics associated with verified impacts among players with and without headgear during competition.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

A total of 49 female high school participants (mean age, 16.2 ± 1.2 years; mean height, 1.66 ± 0.05 m; mean weight, 61.2 ± 6.4 kg) volunteered for this study, which took place during the 2016 (no headgear; 18 games) and 2017 (headgear; 15 games) seasons. Wearable sensors synchronized with video verification were used. Descriptive statistics, impact rates, and chi-square analyses described impacts and game-play characteristics among players with and without headgear. Differences in mean peak linear acceleration (PLA) and peak rotational velocity (PRV) between the no headgear and headgear conditions were evaluated using a linear generalized estimating equation regression model to control for repeated within-player measurements.

Results:

Overall, 649 sensor-instrumented player-games were recorded. A total of 204 impacts ≥20g recorded by the wearable sensors were verified with video analysis (102 no headgear; 102 headgear). Most impacts were imparted to the player’s body (n = 152; 74.5%) rather than to the player’s head (n = 52; 25.5%). Impact rates per player-game did not vary between the no headgear and headgear conditions (0.30 vs 0.34, respectively; impact rate ratio, 0.88 [95% CI, 0.37-2.08]). There was no association between impact frequency by mechanism or penalties administered between the no headgear and headgear conditions for overall or direct head impacts. The generalized estimating equation model estimated a significant reduction in mean impact magnitudes overall (PLA: –7.9g [95% CI, –13.3 to –2.5]; PRV: –212 deg/s [95% CI, –359 to –64]) with headgear relative to no headgear. No game-related concussions were reported during this study.

Conclusion:

Lacrosse headgear use was associated with a reduction in the magnitude of overall impacts but not a significant change in the rate of impacts, how they occur, or how penalties were administered for impacts sustained during competition. Further research is needed with a larger sample and different levels of play to evaluate the consequences of headgear use in girls’ lacrosse.

The Hammer and the Nail: Biomechanics of Striking and Struck Canadian University Football Players

This study sought to evaluate head accelerations in both players involved in a football collision. Players on two opposing Canadian university teams were equipped with helmet mounted sensors during one game per season, for two consecutive seasons. A total of 276 collisions between 58 instrumented players were identified via video and cross-referenced with sensor timestamps. Player involvement (striking and struck), impact type (block or tackle), head impact location (front, back, left and right), and play type were recorded from video footage. While struck players did not experience significantly different linear or rotational accelerations between any play types, striking players had the highest linear and rotational head accelerations during kickoff plays (p ≤ .03). Striking players also experienced greater linear and rotational head accelerations than struck players during kickoff plays (p = .001). However, struck players experienced greater linear and rotational accelerations than striking players during kick return plays (p ≤ .008). Other studies have established that the more severe the head impact, the greater risk for injury to the brain. This paper's results highlight that kickoff play rule changes, as implemented in American college football, would decrease head impact exposure of Canadian university football athletes and make the game safer.

The Effect of Sub-Concussive Impacts during a Rugby Tackling Drill on Brain Function

Concussion is known to detrimentally affect brain health. Rugby tackles commonly occur with high collision force between tackler and ball carrier, and low impact head contact is not uncommon. Cognitive deficits following a bout of soccer ball heading has been attributed to the impact and termed sub-concussion. Although soccer ball heading studies provide evidence for acute effects of sub-concussion, it is unknown whether this phenomenon occurs following rugby tackles. This study investigates the acute effects of rugby tackles on brain function and balance in rugby players. Twenty-six volunteers were assigned to either the ball carrier (9), tackler (9) or control (8) group. Controls performed running without the tackle. Outcome measures included corticomotor function using transcranial magnetic brain stimulation (TMS) and balance was assessed by a series of tasks performed on a NeuroCom Balance Master before and immediately after a tackle training drill. Following the tackling bout, the cortical silent period (cSP) increased for the tacklers with no change for ball carrier and control groups, and no differences between groups for balance measures were observed. Lengthening of cSP observed in the tacklers following the bout has been reported in studies of concussion and may indicate long term detrimental effects.

Future Directions in Sports-Related Concussion Management

This article focuses on 3 concepts that continue to be investigated in the search for the holy grail of concussion-a valid diagnostic test. Imaging advances are discussed with optimism that functional MRI and diffusion tensor imaging may be available clinically. Biomarkers and the use of genetic tests are covered. Sideline accelerometer use may help steer discussions of head trauma risk once technology exists to accurately estimate acceleration of the brain. In the meantime, strategies including allowing athletes to be substituted out of games for an evaluation and video review in elite sports can improve recognition of sports-related concussion.

Do Head Injury Biomechanics Predict Concussion Clinical Recovery in College American Football Players?

Identifying the associations between head impact biomechanics and clinical recovery may inform better head impact monitoring procedures and identify athletes who may benefit from early treatments aimed to enhance recovery. The purpose of this study was to test whether head injury biomechanics are associated with clinical recovery of symptom severity, balance, and mental status, as well as symptom resolution time (SRT) and return-to-participation (RTP) time. We studied 45 college American football players (n = 51 concussions) who sustained an incident concussion while participating in a multi-site study. Player race/ethnicity, prior concussion, medical history, position, body mass index, event type, and impact location were covariates in our multivariable analyses. Multivariable negative binomial regression models analyzed associations between our study outcomes and (1) injury-causing linear and rotational head impact severity, (2) season repetitive head impact exposure (RHIE), and (3) injury day RHIE. Median SRT was 6.1 days (IQR 5.8 days, n = 45) and median RTP time was 12.3 days (IQR 7.8 days, n = 36) across our study sample. RTP time was 86% (Ratio 1.86, 95% CI [1.05, 3.28]) longer in athletes with a concussion history. Offensive players had SRTs 49% shorter than defensive players (Ratio 0.51, 95% CI [0.29, 0.92]). Per-unit increases in season RHIE were associated with 22% longer SRT (Ratio 1.22, 95% CI [1.09, 1.36]) but 28% shorter RTP time (Ratio 0.72, 95% CI [0.56, 0.93]). No other head injury biomechanics predicted injury recovery.

The possible role of hydration in concussions and long-term symptoms of concussion for athletes. A review of the evidence

The purpose of this review is to address what is known, speculated, and hypothesized regarding the issue of hydration and concussions. Based on the question, “What impact does hydration have on the relative risk for suffering concussive injuries along with long-term ramifications that have been associated with concussive (and repeated subconcussive) traumas to the cerebral cortex?,” a search of available literature was performed through June 2019. Deducing from the available literature, we can stipulate that changes in hydration within the cerebral cortex increase the likelihood for disruption of neurofilament proteins, dysregulation of membrane dynamics of the neurons and exacerbate inflammation responses following head trauma. As such, it can be speculated that differences in incidence rates may be attributed to difference in tissue fluid based on athlete demographics, level of whole-body water balance, and degree of tissue dehydration more than selection of sport. Moreover, tissue hydration in combination with other inflammation factors provides the scaffolding for the development of long-term issues (e.g. chronic traumatic encephalopathy) associated with repetitive head trauma in athletes.