Ten-Word List Performance in Healthy Athletes and Athletes at 3-to-5 Days Following Concussion.

OBJECTIVE: Although the word recall component of the Sport Concussion Assessment Tool (SCAT) was updated from 5-to-10 words, its clinical utility across athletic populations remains unknown. The purpose of this study was to provide normative data on the SCAT-5 10-word test and examine its discriminative ability between healthy university level athletes and those with sport-related concussion (SRC). DESIGN: Cross-sectional. SETTING: University. PARTICIPANTS: Three hundred sixty-three (363, M = 220, F = 153) healthy athletes and 49 (M = 30, F = 19) athletes following SRC. INDEPENDENT VARIABLE: Healthy athletes measured preseason were compared with athletes following an SRC (median = 4.0 days postinjury). MAIN OUTCOME MEASURE: Ten-word list performance from the SCAT-5. RESULTS: There were no significant differences in either immediate ( P = 0.228, Cohen's D = 0.18) or delayed ( P = 0.908, Cohen's D = 0.02) recall tests between athletes with SRC and healthy athletes; the null findings extended to both the male and female subset comparisons. Among healthy athletes, females outperformed males on both immediate (mean difference = 1.0, P < 0.001) and delayed (mean difference = 0.5, P = 0.006) recall tasks. CONCLUSION: Concussion does not seem to impact immediate or delayed recall of the 10-word list in the subacute period following injury. Practitioners should be mindful of sex differences and the time point of administration following injury.

Cannabis, alcohol and cigarette use during the acute post-concussion period.

Objective: To document the prevalence of acute post-concussion cannabis, alcohol and cigarette use and their association with clinical recovery and symptom burden.Methods: A prospective cohort study was conducted. Concussions were physician-diagnosed and presented to the emergency department and concussion clinic within 7 days post-injury. Participants were assessed weekly and followed for a minimum 4 weeks. A survival analysis (using physician-determined recovery to both cognitive and physical activities) in addition to a weekly symptom score analysis was conducted.Results: A total of 307 acute concussions with a mean age of 33.7 years (SD, 13.0) were included. Acute post-concussion cannabis, alcohol and cigarette use were identified in 43 (14.0%), 125 (40.7%) and 61 (19.9%) individuals. Acute cannabis, alcohol and cigarette use were not associated with recovery to cognitive (p > .05) or physical activity (p > .05). Acute cigarette use was associated with a higher unadjusted symptom severity score at week1 (p = .003). Acute cannabis use was associated with lower symptom severity scores at week-3 (p = .061) and week-4 (p = .029).Conclusion: In conclusion, cannabis, alcohol and cigarette use were prevalent in the acute period post-concussion; however, were not observed to impact recovery within the first 4 weeks post-injury. Amongst unrecovered individuals, acute cannabis use was associated with lower symptom burden, while cigarette use was associated with greater initial symptom burden.

Branched Chain Amino Acids (BCAAs) and Traumatic Brain Injury: A Systematic Review.

BACKGROUND: Despite the prevalence of traumatic brain injury (TBI), pharmaceutical treatment options for brain injury remain limited. However, nutritional intervention (such as with branched chain amino acids [BCAAs]) has emerged as a promising treatment option for TBI. OBJECTIVES: (1) To determine whether TBI patients have lower levels of endogenous BCAAs postinjury; and (2) to evaluate whether post-TBI BCAA supplementation improves clinical outcome. DESIGN: A systematic review of primary research articles examining the relationship between BCAAs and TBI recovery indexed in Ovid/MEDLINE, EMBASE, and PsycINFO. RESULTS: Of the 11 studies identified, 3 examined the effects of TBI on endogenous BCAA levels and consistently reported that BCAA concentrations were depressed postinjury. The remaining 8 studies examined the effects of BCAA supplementation on TBI outcome in animals (n = 3) and humans (n = 5). The animal studies (in mild-to-moderate TBI) showed that BCAAs improved post-TBI outcome. Similar results were found in human trials (conducted primarily in patients with severe TBI), with 4 of the 5 studies reporting improved outcome with BCAA supplementation. CONCLUSION: Although our review demonstrates an overall positive association between BCAAs and TBI outcome, the evidence of the efficacy of supplementation has been limited to severe TBI. To date, there is insufficient evidence to determine the benefits of BCAAs in mild TBI. Given the high frequency of mild TBI and the promise of BCAAs as an intervention in severe TBI, future research should examine the effects of BCAAs in milder brain injury.

A review of the neuroprotective role of vitamin D in traumatic brain injury with implications for supplementation post-concussion.

BACKGROUND: Nutritional interventions are promising treatment adjuncts in the management of concussion. Vitamin D (VDH) supplementation has demonstrated neuroprotective properties in multiple models of acquired brain injury. OBJECTIVE: Review the neuroprotective role of VDH supplementation following traumatic brain injury (TBI). METHODS: A Medline search was conducted to review manuscripts investigating the influence of VDH status or supplementation on TBI outcomes. RESULTS: The search identified 165 studies, of which five were included. Four manuscripts studied a rodent model of TBI, while one studied a clinical sample. Vitamin D monotherapy independently reduced inflammation and neuronal injury following TBI, with a more robust effect observed in combination with progesterone (PROG). One study demonstrated VDH deficiency exacerbates post-TBI inflammatory response. One study in a clinical sample found combination therapy superior to PROG alone or placebo in improving outcomes after severe TBI. One study observed a more robust response to low-dose VDH compared to high-dose VDH when given in combination with PROG. CONCLUSION: A protective role for VDH and a vitamin D sufficient status was identified for numerous outcomes following TBI. However, VDH supplementation cannot be recommended at this time to improve outcomes following TBI.

The role of apolipoprotein E episilon (ε)-4 allele on outcome following traumatic brain injury: A systematic review.

BACKGROUND: The apolipoprotein E gene (APOE) has emerged as a candidate for prognosticating traumatic brain injury (TBI) recovery, with APOEε4 identified as a susceptibility marker for poor outcome, despite large discrepancy in its reported influence post-TBI. METHODS: A systematic review was conducted, including all primary articles investigating the role of APOEε4 on TBI outcome. A total of 65 studies were included, including 24 predominantly investigating mild (mTBI), seven moderate (modTBI) and 33 severe (sTBI); severity was not reported in one study. RESULTS: In mTBI studies, the association between APOEε4 and post-TBI outcome was concluded as non-contributory in 14 studies (58.3%), hazardous in nine (37.5%) and protective in one (4.2%). In sTBI studies, the role of APOEε4 was hazardous in 21 (63.6%), non-contributory in nine (27.3%) and protective in three (9.1%). Of the seven studies investigating dementia outcomes, four observed a hazardous association with APOEε4, while three reported no association. Six studies examined Alzheimer's dementia pathology, of which three reported a hazardous influence of APOEε4. CONCLUSIONS: The influence of APOEε4 on neuropsychological testing, functional outcome and in paediatric populations was incongruous. This review supports the majority of research indicating APOEε4 adversely influences recovery following TBI, particularly with respect to dementia-related outcomes and outcomes following sTBI.

Interrater agreement of an observational tool to code knockouts and technical knockouts in mixed martial arts.

OBJECTIVE: Interrater agreement evaluation of a tool to document and code the situational factors and mechanisms of knockouts (KOs) and technical knockouts (TKOs) in mixed martial arts (MMA). DESIGN: Retrospective case series. SETTING: Professional MMA matches from the Ultimate Fighting Championship-2006-2012. PARTICIPANTS: Two nonmedically trained independent raters. MAIN OUTCOME MEASURES: The MMA Knockout Tool (MMA-KT) consists of 20 factors and captures and codes information on match characteristics, situational context preceding KOs and TKOs, as well as describing competitor states during these outcomes. The MMA-KT also evaluates the mechanism of action and subsequent events surrounding a KO. RESULTS: The 2 raters coded 125 unique events for a total of 250 events. The 8 factors of Part A had an average κ of 0.87 (SD = 0.10; range = 0.65-0.98); 7 were considered "substantial" agreement and 1 "moderate." Part B consists of 12 factors with an average κ of 0.84 (SD = 0.16; range = 0.59-1.0); 7 classified as "substantial" agreement, 4 "moderate," and 1 "fair." The majority of the factors in the MMA-KT demonstrated substantial interrater agreement, with an average κ of 0.86 (SD = 0.13; range = 0.59-1.0). CONCLUSIONS: The MMA-KT is a reliable tool to extract and code relevant information to investigate the situational factors and mechanism of KOs and TKOs in MMA competitions.

Premature return to play and return to learn after a sport-related concussion: physician's chart review.

OBJECTIVE: To determine what proportion of patients experience an exacerbation of their symptoms as a result of premature return to play (RTP) and return to learn (RTL) following sport-related concussions. DESIGN: Retrospective study of electronic medical records from the office-based practice of one family and sport medicine physician who had systematically provided recommendations for cognitive and physical rest based on existing consensus recommendations. Two blinded authors independently reviewed each chart, which included Sport Concussion Assessment Tool (SCAT) and SCAT2 symptom self-report forms to determine whether an athlete had returned to play or learn prematurely. If there was a discrepancy between the 2 reviewers then a third author reviewed the charts. SETTING: A sport medicine and family practice in Ontario. The physician assessed sport-related concussions after self-referral or referral from other primary care physicians, teams, and schools. PARTICIPANTS: A total of 170 charts of 159 patients were assessed for sport-related concussion during a 5-year period (April 2006 to March 2011). All participants were students who were participating in sports at the time of injury. There were 41 concussions in elementary students, 95 concussions in high school students, and 34 concussions in college or university students. MAIN OUTCOME MEASURES: Premature RTP and RTL were defined as chart records documenting the recurrence or worsening of symptoms that accompanied the patients' RTP or RTL. Measures were compared using the earliest available SCAT forms and self-reporting. RESULTS: In 43.5% of concussion cases, the patient returned to sport too soon and in 44.7% of concussion cases, the patient returned to school too soon. Patients with a history of previous concussion required more days of rest before being permitted to participate in any physical activity than those patients without a previous history of concussion. Elementary school students required fewer days of rest before being permitted to return to any physical activity compared with high school students and college or university students. CONCLUSION: Currently, physicians recommend restrictions on mental and physical activity following sport-related concussion. This is done without clear guidelines as to what cognitive rest entails for students. Further research is required to determine how to implement a management plan for student athletes to facilitate complete recovery after concussion.

Top journals publishing articles related to drowning prevention: a bibliometric analysis 2000-2022.

BACKGROUND: Drowning is a worldwide problem. Scholarly publications about drowning prevention play a crucial role in bringing data to policy makers and prevention specialists. This study presents a bibliometric analysis of published articles related to unintentional drowning prevention included in the comprehensive, curated injury literature database, SafetyLit®. METHODS: Thorough searches of drowning-related search terms in English and non- English translations identified articles published in journals between 2000 and 2022. RESULTS: There was a 3-fold increase in publications between 2000 and 2022, with 2,937 articles published in 941 journals. Articles were published in 20 different languages. Five journals published 16% of the articles and sixty-one top journals published 50% of the articles. Eighty-nine percent of the top journals were included in PubMed; 82% were indexed in MEDLINE®; and professional areas of expertise of article authors spanned 18 categories. CONCLUSIONS: This study can facilitate journal selection for drowning researchers to ultimately increase the publication of scientific literature globally.

A Multimodal Exertional Test for concussion: a pilot study in healthy athletes.

Introduction: Exertional tests have become a promising tool to assist clinicians in the management of concussions, however require expensive equipment, extensive spaces, and specialized clinician expertise. As such, we developed a test with minimal resource requirements encompassing key elements of sport and physical activity. The purpose of this study was to pilot test the Multimodal Exertional Test (MET) protocol in a sample of healthy interuniversity athletes. Methods: The MET comprises four stages, each featuring three distinct tasks. The test begins with engaging in squats, alternating reverse lunges, and hip hinges (Stage 1). The next stage progressively evolves into executing these tasks within specified time limits (Stage 2). Following this, the test advances to a stage that incorporates cognitive tasks (Stage 3), and the final stage demands greater levels of physical exertion, cognition, and multi-directional movements (Stage 4). Heart rate (HR) was obtained during each stage of the MET and participants' symptom severity scores were recorded following each task. Results: Fourteen healthy interuniversity athletes (n = 8 female, n = 6 male) participated in the study. HR was obtained for 10 of the 14 athletes (females: n = 6, males: n = 4). Increases in average and maximum HR were identified between pre-MET and Stage 1, and between Stages 3 and 4. Consistent with the tasks in each stage, there were no increases in average and maximum HR observed between MET Stages 1 to 3. Female athletes exhibited higher average and maximum HRs compared to male athletes during all four stages. All 14 athletes reported minimal changes in symptom severity following each task. Conclusion: Among healthy athletes, the MET elicits an increase in average and maximum HR throughout the protocol without symptom provocation. Female athletes exhibit higher HRs during all four stages in comparison to male athletes.

The Toronto Concussion Study: a prospective investigation of characteristics in a cohort of adults from the general population seeking care following acute concussion, 2016-2020.

Purpose: There is limited research regarding the characteristics of those from the general population who seek care following acute concussion. Methods: To address this gap, a large cohort of 473 adults diagnosed with an acute concussion (female participants = 287; male participants = 186) was followed using objective measures prospectively over 16 weeks beginning at a mean of 5.1 days post-injury. Results: Falls were the most common mechanism of injury (MOI) (n = 137, 29.0%), followed by sports-related recreation (n = 119, 25.2%). Male participants were more likely to be injured playing recreational sports or in a violence-related incident; female participants were more likely to be injured by falling. Post-traumatic amnesia (PTA) was reported by 80 participants (16.9 %), and loss of consciousness (LOC) was reported by 110 (23.3%). In total, 54 participants (11.4%) reported both PTA and LOC. Male participants had significantly higher rates of PTA and LOC after their injury compared to their female counterparts. Higher initial symptom burden was associated with a longer duration of recovery for both male and female participants. Female participants had more symptoms and higher severity of symptoms at presentation compared to male participants. Female participants were identified to have a longer recovery duration, with a mean survival time of 6.50 weeks compared to 5.45 weeks in male participants (p < 0.0001). A relatively high proportion of female and male participants in this study reported premorbid diagnoses of depression and anxiety compared to general population characteristics. Conclusion: Although premorbid diagnoses of depression and/or anxiety were associated with higher symptom burden at the initial visit, the duration of symptoms was not directly associated with a pre-injury history of psychological/psychiatric disturbance. This cohort of adults, from the general population, seeking care for their acute concussion attained clinical and functional recovery over a period of 4-12 weeks.

Randomized controlled trial of early aerobic exercise following sport-related concussion: Progressive percentage of age-predicted maximal heart rate versus usual care.

OBJECTIVE: To examine the effect of a readily accessible, structured aerobic exercise intervention on days to asymptomatic status and days to medical clearance compared to usual care exercise prescription in a cohort of adolescents and young adults following sport-related concussion (SRC). METHODS: A longitudinal, randomized, non-blinded clinical trial consisting of a structured aerobic exercise protocol (SAEP) group and a usual care exercise prescription (UCEP) group. Participants in the SAEP group underwent an exercise protocol including 8 sessions over 11 days progressing in duration and intensity stepwise based on participants' age-predicted maximal heart rate. Symptom follow-ups were on days 7, 14, 21, and 28. The primary outcome measures of the study were days to asymptomatic status and days to medical clearance, while the secondary outcome measure was symptom severity on days 7, 14, 21, and 28. RESULTS: 38 participants (SAEP, n = 20; UCEP, n = 19) were recruited and completed all follow-up appointments. Compared to the UCEP group, the SAEP had a faster time to asymptomatic status with 96% posterior probability. In addition, the SAEP group displayed an earlier time to medical clearance with 93% posterior probability. While symptom severity scores did not differ between groups at enrolment (SAEP symptom severity, 30; UCEP, 29), they were subsequently lower in the SAEP group at all assessments throughout the trial with 100% posterior probability. CONCLUSIONS: An aerobic exercise protocol based on percentages of age-predicted maximum heart rate is a safe and effective treatment for reducing symptoms and can be initiated during the first week following SRC. TRIAL REGISTRATION: ClinicalTrials.gov, no. NCT02969824.

Controlled search term vocabularies for finding articles relevant to injury prevention and safety promotion.

OBJECTIVES: To assess the usefulness of the controlled vocabularies of PubMed/MEDLINE and PsycINFO for finding articles on injury prevention and safety promotion (IPSP) topics and to identify specific indexing problems that can contribute to incomplete retrieval. METHODS: Professional reference librarians provided search strategies for finding articles relevant to five topics pertaining to the injury prevention field in the two bibliographic databases. The results of implementing these search strategies were compared with the results of a presumptive gold standard-serial textword searches on the same topics. The index terms assigned to the articles that were missed by the librarian strategies were examined. RESULTS: The search products of the librarian-constructed search strategies identified 34-91% of the IPSP-relevant articles that were identified through serial textword searches of the two databases. Specific indexing issues were found to contribute to this loss. CONCLUSIONS: Librarians bring expertise to searching, but irregular or incomplete indexing can limit the product of even well-constructed searches for articles on IPSP topics.

Can Sport Concussion Assessment Tool (SCAT) Symptom Scores Be Converted to Rivermead Post-concussion Symptoms Questionnaire (RPQ) Scores and Vice Versa? Findings From the Toronto Concussion Study.

Background: The Rivermead Post-Concussion Symptoms Questionnaire (RPQ) and the Sports Concussion Assessment Tool (SCAT) are widely used self-report tools assessing the type, number, and severity of concussion symptoms. There are overlapping symptoms and domains, though they are scored differently. The SCAT consists of 22 questions with a 7-point Likert scale for a total possible score 132. The RPQ has 16 questions and a 5-point Likert scale for a total of 64 possible points. Being able to convert between the two scores would facilitate comparison of results in the concussion literature. Objectives: To develop equations to convert scores on the SCAT to the RPQ and vice versa. Methods: Adults (17-85 years) diagnosed with a concussion at a referring emergency department were seen in the Hull-Ellis Concussion and Research Clinic, a rapid access concussion clinic at Toronto Rehab-University Health Network (UHN) Toronto Canada, within 7 days of injury. The RPQ and SCAT symptom checklists as well as demographic questionnaires were administered to all participants at Weeks 1, 2, 3, 4, 5, 6, 7, 8, 12, 16. Results: 215 participants had 1,168 matched RPQ and SCAT assessments. Total scores of the RPQ and the SCAT had a rho = 0.91 (p < 0.001); correlations were lower for sub-scores of specific symptom domains (range 0.74-0.87, p < 0.001 for all domain comparisons). An equation was derived to calculate SCAT scores using the number and severity of symptoms on the RPQ. Estimated scores were within 3 points of the observed total score on the SCAT. A second equation was derived to calculate the RPQ from the proportion weighted total score of the SCAT. This equation estimated corresponding scores within 3 points of the observed score on the RPQ. Conclusions: The RPQ and SCAT symptom checklists total scores are highly correlated and can be used to estimate the total score on the corresponding assessment. The symptom subdomains are also strongly correlated between the 2 scales however not as strongly correlated as the total score. The equations will enable researchers and clinicians to quickly convert between the scales and to directly compare concussion research findings.

Peripheral blood neuroendocrine hormones are associated with clinical indices of sport-related concussion.

The purpose of this study was to evaluate the relationship between neuroendocrine hormones and clinical recovery following sport-related concussion (SRC). Ninety-five athletes (n = 56 male, n = 39 female) from a cohort of 11 interuniversity sport teams at a single institution provided blood samples; twenty six athletes with SRC were recruited 2-7 days post-injury, and 69 uninjured athletes recruited prior to the start of their competitive season. Concentrations of seven neuroendocrine hormones were quantitated in either plasma or serum by solid-phase chemiluminescent immunoassay. The Sport Concussion Assessment Tool version 5 (SCAT-5) was used to evaluate symptoms at the time of blood sampling in all athletes. Multivariate partial least squares (PLS) analyses were used to evaluate the relationship between blood hormone concentrations and both (1) time to physician medical clearance and (2) initial symptom burden. A negative relationship was observed between time to medical clearance and both dehydroepiandrosterone sulfate (DHEA-S) and progesterone; a positive relationship was found between time to medical clearance and prolactin. Cognitive, somatic, fatigue and emotion symptom clusters were associated with distinct neuroendocrine signatures. Perturbations to the neuroendocrine system in athletes following SRC may contribute to initial symptom burden and longer recovery times.

Influence of Extrinsic Risk Factors on National Football League Injury Rates.

BACKGROUND: The risk of injury associated with American football is significant, with recent reports indicating that football has one of the highest rates of all-cause injury, including concussion, of all major sports. There are limited studies examining risk factors for injuries in the National Football League (NFL). PURPOSE: To identify risk factors for NFL concussions and musculoskeletal injuries. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Injury report data were collected prospectively for each week over the 2012-2013 and 2013-2014 regular seasons for all 32 teams. Poisson regression models were used to identify the relationship between predetermined variables and the risk of the 5 most frequent injuries (knee, ankle, hamstring, shoulder, and concussion). RESULTS: A total of 480 games or 960 team games (TGs) from the 2012-2013 and 2013-2014 regular seasons were included in this study. A trend to an increasing risk of concussion and TG ankle injury with decreasing mean game-day temperature was observed. The risk of TG concussion (incidence rate ratio [IRR], 2.16; 95% CI, 1.35-3.45; P = .001) and TG ankle injury (IRR, 1.48; 95% CI, 1.10-1.98; P = .01) was significantly greater for TGs played at a mean game-day temperature of ≤9.7°C (≤49.5°F) compared with a mean game-day temperature of ≥21.0°C (≥69.8°F). The risk of TG shoulder injury was significantly increased for TGs played on grass surfaces (IRR, 1.36; 95% CI, 1.02-1.81; P = .038) compared with synthetic surfaces. The risk of TG injury was not associated with time in season, altitude, time zone change prior to game, or distance traveled to a game. CONCLUSION: This study evaluated extrinsic risk factors for injury in the NFL. A hazardous association was identified for risk of concussion and ankle injury with colder game-day temperature. Further research should be conducted to substantiate this relationship and its potential implication for injury prevention initiatives.

Descriptive Epidemiology of Musculoskeletal Injuries and Concussions in the National Football League, 2012-2014.

BACKGROUND: The risk of all-cause injury and concussion associated with football is significant. The National Football League (NFL) has implemented changes to increase player safety warranting investigation into the incidence and patterns of injury. PURPOSE: To document the incidence and patterns of all-cause injury and concussions in the NFL. STUDY DESIGN: Descriptive epidemiology study. METHODS: Injury data were collected prospectively from official NFL injury reports over 2 regular seasons from 2012 to 2014, with identification of injury incidence rates and patterns. Concussion rate ratios were calculated using previously reported NFL rates. RESULTS: A total of 4284 injuries were identified, including 301 concussions. The all-cause injury rate was 395.8 per 1000 athletes at risk (AAR) and concussion incidence was 27.8 per 1000 AAR. Only 2.3% of team games were injury free. Wide receivers, tight ends, and defensive backs had the highest incidence of injury and concussion. Concussion incidence was 1.61-fold higher in 2012 to 2014 compared with 2002 to 2007. The knee was injured most frequently, followed by the ankle, hamstring, shoulder, and head. CONCLUSION: The incidence of all-cause injury and concussion in the NFL is significant. Concussion injury rates are higher than previous reports, potentially reflecting an improvement in recognition and awareness. Injury prevention efforts should continue to reduce the prevalence of injury associated with football.

Head Trauma in Mixed Martial Arts.

BACKGROUND: Mixed martial arts (MMA) is a full combative sport with a recent global increase in popularity despite significant scrutiny from medical associations. To date, the empirical research of the risk of head injuries associated with this sport is limited. Youth and amateur participation is growing, warranting investigation into the burden and mechanism of injuries associated with this sport. PURPOSE: (1) To determine the incidence, risk factors, and characteristics of knockouts (KOs) and technical knockouts (TKOs) from repetitive strikes in professional MMA; and (2) to identify the mechanisms of head trauma and the situational factors that lead to KOs and TKOs secondary to repetitive strikes through video analysis. STUDY DESIGN: Descriptive epidemiology study. METHODS: Competition data and video records for all KOs and TKOs from numbered Ultimate Fighting Championship MMA events (n = 844) between 2006 to 2012. Analyses included (1) multivariate logistic regression to investigate factors associated with an increased risk of sustaining a KO or TKO secondary to repetitive strikes and (2) video analysis of all KOs and TKOs secondary to repetitive strikes with descriptive statistics. RESULTS: During the study period, the KO rate was 6.4 per 100 athlete-exposures (AEs) (12.7% of matches), and the rate of TKOs secondary to repetitive strikes was 9.5 per 100 AEs (19.1% of matches), for a combined incidence of match-ending head trauma of 15.9 per 100 AEs (31.9% of matches). Logistic regression identified that weight class, earlier time in a round, earlier round in a match, and older age were risk factors for both KOs and TKOs secondary to repetitive strikes. Match significance and previously sustained KOs or TKOs were also risk factors for KOs. Video analysis identified that all KOs were the result of direct impact to the head, most frequently a strike to the mandibular region (53.9%). The average time between the KO-strike and match stoppage was 3.5 seconds (range, 0-20 seconds), with losers sustaining an average of 2.6 additional strikes (range, 0-20 strikes) to the head. For TKOs secondary to strikes, in the 30-second interval immediately preceding match stoppage, losers sustained, on average, 18.5 strikes (range, 5-46 strikes), with 92.3% of these being strikes to the head. CONCLUSION: Rates of KOs and TKOs in MMA are higher than previously reported rates in other combative and contact sports. Public health authorities and physicians should be cognizant of the rates and mechanisms of head trauma. Preventive measures to lessen the risks of head trauma for those who elect to participate in MMA are described.