Cumulative Head Research Articles

Chronic Traumatic Encephalopathy in Sports Practice: A Literature Review

AbstractChronic traumatic encephalopathy (CTE) is a neurodegenerative syndrome caused by repetitive and cumulative head trauma. Due to the widespread practice of contact and collision sports, a discussion of the long-term repercussions of repeated head trauma is imperative. The present literature review, performed through the SciELO, PUBMED, and BVS-Bireme databases, includes studies conducted since the year 2000, which established the relationship between CTE and the practice of sports. The diagnosis of CTE was notably present in individuals practicing sports that involve repeated traumatic brain injuries. The noticeable changes triggered by CTE include a series of clinical and neuropathological manifestations that can help in the differentiation from other tauopathies.

Dual-Task Gait Performance Following Head Impact Exposure in Male and Female Collegiate Rugby Players.

BackgroundGait impairments have been well-studied in concussed athletes. However, the sex-specific effect of cumulative head impacts on gait is not well understood. When a cognitive task is added to a walking task, dual-task gait assessments can help amplify deficits in gait and are representative of tasks in everyday life. Dual-task cost is the difference in performance from walking (single-task) to walking with a cognitive load (dual-task).PurposeThe objectives of this study were to explore the differences between sexes in 1) dual-task gait metrics, 2) gait metric changes from pre-season to post-concussion and post-season, and 3) the dual-task costs associated with gait metrics.Study DesignCross-sectional studyMethodsOver two seasons, 77 female athlete-seasons and 64 male athlete-seasons from collegiate club rugby teams participated in this study. Subjects wore inertial sensors and completed walking trials with and without a cognitive test at pre-season, post-season, and post-concussion (if applicable).ResultsFemales athletes showed improvement in cadence (mean = 2.7 step/min increase), double support time (mean = -0.8% gait cycle time decrease), gait speed (mean = 0.1 m/s increase), and stride length (mean = 0.2 m increase) in both task conditions over the course of the season (p < 0.030). Male athletes showed no differences in gait metrics over the course of the season, except for faster gait speeds and longer stride lengths in the dual-task condition (p < 0.034). In all four gait characteristics, at baseline and post-season, females had higher dual-task costs (mean difference = 4.4, p < 0.003) than the males.ConclusionsThis results of this study showed little evidence suggesting a relationship between repetitive head impact exposure and gait deficits. However, there are sex-specific differences that should be considered during the diagnosis and management of sports-related concussion.Level of EvidenceLevel 2b

Salivary S100 calcium-binding protein beta (S100B) and neurofilament light (NfL) after acute exposure to repeated head impacts in collegiate water polo players

Blood-based biomarkers of brain injury may be useful for monitoring brain health in athletes at risk for concussions. Two putative biomarkers of sport-related concussion, neurofilament light (NfL), an axonal structural protein, and S100 calcium-binding protein beta (S100B), an astrocyte-derived protein, were measured in saliva, a biofluid which can be sampled in an athletic setting without the risks and burdens associated with blood sampled by venipuncture. Samples were collected from men’s and women’s collegiate water polo players (n = 65) before and after a competitive tournament. Head impacts were measured using sensors previously evaluated for use in water polo, and video recordings were independently reviewed for the purpose of validating impacts recorded by the sensors. Athletes sustained a total of 107 head impacts, all of which were asymptomatic (i.e., no athlete was diagnosed with a concussion or more serious). Post-tournament salivary NfL was directly associated with head impact frequency (RR = 1.151, p = 0.025) and cumulative head impact magnitude (RR = 1.008, p = 0.014), while controlling for baseline salivary NfL. Change in S100B was not associated with head impact exposure (RR < 1.001, p > 0.483). These patterns suggest that repeated head impacts may cause axonal injury, even in asymptomatic athletes.

Exposure to Head Impacts and Cognitive and Behavioral Outcomes in Youth Tackle Football Players Across 4 Seasons

Repetitive head impacts have been posited to contribute to neurocognitive and behavioral difficulties in contact sport athletes. To identify associations between cognitive and behavioral outcomes and head impacts measured in youth tackle football players over 4 seasons of play. This prospective cohort study was conducted from July 2016 through January 2020, spanning 4 football seasons. The setting was a youth tackle football program and outpatient medical clinic. Players were recruited from 4 football teams composed of fifth and sixth graders, and all interested players who volunteered to participate were enrolled. Data analysis was performed from March 2020 to June 2021. Impacts were measured using helmet-based sensors during practices and games throughout 4 consecutive seasons of play. Impacts were summed to yield cumulative head impact gravitational force equivalents per season. Ten cognitive and behavioral measures were completed before and after each football season. There were 70 male participants aged 9 to 12 years (mean [SD] age, 10.6 [0.64] years), with 18 completing all 4 years of the study. At the post-season 1 time point, higher cumulative impacts were associated with lower self-reported symptom burden (β = -0.6; 95% CI, -1.0 to -0.2; P = .004). After correcting for multiple comparisons, no other associations were found between impacts and outcome measures. At multiple times throughout the study, premorbid attention-deficit/hyperactivity disorder, anxiety, and depression were associated with worse cognitive or behavioral scores, whereas a premorbid headache disorder or history of concussion was less often associated with outcomes. In this cohort of youth tackle football players, premorbid conditions, including attention-deficit/hyperactivity disorder, anxiety, and depression, were associated with cognitive and behavioral outcomes more often than cumulative impact.

Age at League Entry and Early All-Cause Mortality among National Football League Players

Background: A growing body of research suggests that American football players are exposed to higher cumulative head impact risk as competition level rises. Related literature finds that head impacts absorbed by youth, adolescent, and emerging adult players are associated with elevated risk of long-term health problems (e.g., neurodegenerative disease onset). Most National Football League (NFL) players enter the League as emerging adults (18–24 years old), a period of continued cognitive and overall physical development. However, no prior research has studied the effect of age-at-entry on long-term NFL player health. Hypothesis/Purpose: This study assesses whether early NFL player age-at-entry is associated with increased risk of early all-cause mortality, controlling for player position, BMI, year-of-entry, birth year, and NFL Draft round (expected ability upon League entry). Study Design: This retrospective cohort study included 9049 players who entered the NFL from 1970–2017 and subsequently played at least one game. The variables whether deceased, age-at-death, age-at-entry, and controls were collected from Pro Football Reference website, a leading data site for American football that has been used extensively in the literature. Data collection began on 13 July 2017, and follow-up ended on 1 July 2018. Statistical analysis was performed from 10 March 2020 to 3 August 2020. Data was validated by checking a large sub-sample of data points against alternative sources such as NFL.com and NFLsavant.com. Methods: Cox proportional hazards regression models were used to examine variation in death hazard by NFL player age-at-entry, conditional upon a full set of controls. Results: Conditional on controls, Cox regression results indicate that a one-year increase in age-at-entry was significantly associated with a 14% decreased hazard-of-death (H.R., 0.86; 95% CI, 0.74–0.98). Among relatively young entering players, the increased hazard appears to be concentrated in the first quartile of players by age at League entry (20.2 to 22.3 years). Players not in this quartile exhibited a decreased hazard-of-death (H.R., 0.74; 95% CI, 0.57–0.97) compared with players who entered at a relatively young (first quartile) age. Conclusion: An earlier age-at-entry is associated with an increased hazard-of-death among NFL players. Currently, the NFL regulates age-at-entry only indirectly by requiring players to be 3 years removed from high school before becoming NFL Draft-eligible. Implementing a minimum age at entry for NFL players of 22 years and 4 months at beginning of season is expected to result in reduced mortality. What is known about this subject? There are no prior studies on the effects of NFL player age-at-entry on early mortality risk. What this study adds to existing knowledge: This study determines whether entering the NFL at an age of physical and physiological development is related to early mortality risk.

Assessment Of Neurologic Function In Mixed Martial Arts Athletes

Mixed martial arts (MMA) is a combat sport in which participants routinely incur head impacts that may put them at risk for acute brain injury and/or neurodegenerative brain disease. MMA athletes compete rather infrequently, though often train year-round; thus, their brain injury risk is a function of discrete and cumulative head impact exposure during training and competition. Despite MMA athletes being at increased risk for brain injury, their neurologic health has not been well characterized. PURPOSE: To examine if MMA participation is associated with neurologic impairment. METHODS: Seventeen amateur and professional MMA athletes (14 men, 3 women; 25.4 ± 3.5 yr) and seventeen age- and sex-matched healthy control subjects (14 men, 3 women; 26.4 ± 3.3 yr) participated in this study. All participants completed a baseline evaluation using several objective assessments of neurologic function: eye movement speed and accuracy (King-Devick test; KD); near point convergence (Vestibular / Ocular-Motor Screening; NC), eye-hand reaction time (FitLight Trainer; RT), visuomotor ability (FitLight Trainer; VM), static balance (Wii Balance Board; SB), and multiple object tracking speed (NeuroTracker; MOT). MMA athletes completed follow-up assessments at various times post-baseline, including up to three post-fight assessments and/or up to two post-training assessments. Control subjects were tested at time points similar to that of MMA athletes’ post-fight assessments. RESULTS: MMA athletes performed significantly worse than controls on all three vision-related tests (KD [P < 0.001], NC [P = 0.013], and MOT [P < 0.001]) at baseline. MMA athletes also had significantly slower RT (P = 0.008) and VM (P = 0.017) at baseline, while their SB was poorer compared to controls (P ≤ 0.033). Finally, MMA athletes had attenuated improvements in KD and RT (P = 0.013 and P = 0.003 - 0.024, respectively) over time, though both groups improved similarly on all other assessments when controlling for baseline measures. CONCLUSIONS: MMA athletes had deficits in several measures of neurologic function at baseline and throughout serial evaluations compared to age- and sex-matched control participants. These results suggest that MMA participation may be associated with impaired neurologic function.

Head Impact Biomechanics in Youth Flag Football: A Prospective Cohort Study

Background: Youth flag football participation has rapidly grown and is a potentially safer alternative to tackle football. However, limited research has quantitatively assessed youth flag football head impact biomechanics. Purpose: To describe head impact biomechanics outcomes in youth flag football and explore factors associated with head impact magnitudes. Study Design: Cross-sectional study; Level of evidence, 3. Methods: We monitored 52 player-seasons among 48 male flag football players (mean ± SD; age, 9.4 ± 1.1 years; height, 138.6 ± 9.5 cm; mass, 34.7 ± 9.2 kg) across 3 seasons using head impact sensors during practices and games. Sensors recorded head impact frequencies, peak linear (g) and rotational (rad/s2) acceleration, and estimated impact location. Impact rates (IRs) were calculated as 1 impact per 10 player-exposures; IR ratios (IRRs) were used to compare season, event type, and age group IRs; and 95% CIs were calculated for IRs and IRRs. Weekly and seasonal cumulative head impact frequencies and magnitudes were calculated. Mixed-model regression models examined the association between player characteristics, event type, and seasons and peak linear and rotational accelerations. Results: A total of 429 head impacts from 604 exposures occurred across the study period (IR, 7.10; 95% CI, 4.81-10.50). Weekly and seasonal cumulative median head impact frequencies were 1.00 (range, 0-2.63) and 7.50 (range, 0-21.00), respectively. The most frequent estimated head impact locations were the skull base (n = 96; 22.4%), top of the head (n = 74; 17.2%), and back of the head (n = 66; 15.4%). The combined event type IRs differed among the 3 seasons (IRR range, 1.45-2.68). Games produced greater IRs (IRR, 1.24; 95% CI, 1.01-1.53) and peak linear acceleration (mean difference, 5.69g; P = .008) than did practices. Older players demonstrated greater combined event–type IRs (IRR, 1.46; 95% CI, 1.12-1.90) and increased head impact magnitudes than did younger players, with every 1-year age increase associated with a 3.78g and 602.81-rad/s2 increase in peak linear and rotational acceleration magnitude, respectively (P≤ .005). Conclusion: Head IRs and magnitudes varied across seasons, thus highlighting multiple season and cohort data are valuable when providing estimates. Head IRs were relatively low across seasons, while linear and rotational acceleration magnitudes were relatively high.

Exposure to Repetitive Head Impacts Is Associated With Corpus Callosum Microstructure and Plasma Total Tau in Former Professional American Football Players.

Exposure to repetitive head impacts (RHI) is associated with an increased risk of later-life neurobehavioral dysregulation and neurodegenerative disease. The underlying pathomechanisms are largely unknown. To investigate whether RHI exposure is associated with later-life corpus callosum (CC) microstructure and whether CC microstructure is associated with plasma total tau and neuropsychological/neuropsychiatric functioning. Retrospective cohort study. Seventy-five former professional American football players (age 55.2 ± 8.0 years) with cognitive, behavioral, and mood symptoms. Diffusion-weighted echo-planar MRI at 3 T. Subjects underwent diffusion MRI, venous puncture, neuropsychological testing, and completed self-report measures of neurobehavioral dysregulation. RHI exposure was assessed using the Cumulative Head Impact Index (CHII). Diffusion MRI measures of CC microstructure (i.e., free-water corrected fractional anisotropy (FA), trace, radial diffusivity (RD), and axial diffusivity (AD)) were extracted from seven segments of the CC (CC1-7), using a tractography clustering algorithm. Neuropsychological tests were selected: Trail Making Test Part A (TMT-A) and Part B (TMT-B), Controlled Oral Word Association Test (COWAT), Stroop Interference Test, and the Behavioral Regulation Index (BRI) from the Behavior Rating Inventory of Executive Function, Adult version (BRIEF-A). Diffusion MRI metrics were tested for associations with RHI exposure, plasma total tau, neuropsychological performance, and neurobehavioral dysregulation using generalized linear models for repeated measures. RHI exposure was associated with increased AD of CC1 (correlation coefficient (r)=0.32, P< 0.05) and with increased plasma total tau (r= 0.34, P< 0.05). AD of the anterior CC1 was associated with increased plasma total tau (CC1: r= 0.30, P< 0.05; CC2: r= 0.29, P< 0.05). Higher trace, AD, and RD of CC1 were associated with better performance (P< 0.05) in TMT-A (trace, r= 0.33; AD, r= 0.31; and RD, r= 0.28) and TMT-B (trace, r= 0.31; RD, r= 0.34). Higher FA and AD of CC2 were associated with better performance (P< 0.05) in TMT-A (FA, r= 0.36; AD, r= 0.28), TMT-B (FA, r= 0.36; AD, r= 0.27), COWAT (FA, r= 0.36; AD, r= 0.32), and BRI (AD, r= 0.29). These results suggest an association among RHI exposure, CC microstructure, plasma total tau, and clinical functioning in former professional American football players. 3 Technical Efficacy Stage: 1.

Altered Vestibular Balance Function in Combat Sport Athletes.

Combat sports pose a risk for accumulative injuries to the nervous system, yet fighters have remained an understudied population. Here, our purpose was to determine whether repetitive blows to the head have an effect on vestibular balance reflexes in combat sports athletes. We compared lower-limb muscle responses evoked with electrical vestibular stimuluation (EVS) between fighters (boxing/muay thai) and non-fighter controls. Each participant received stochastic vestibular stimulation (0-25 Hz, ±3 mA) over their mastoid processes while they stood relaxed with their head to the left or right. Surface electromyography was recorded from the medial gastrocnemius and soleus muscles bilaterally. Short and medium latency response (SLR/MLR) peaks were significantly delayed in the fighter group compared to controls. SLR and MLR peak amplitudes were also significantly lower in fighters. Fighter-estimated cumulative repetitive head impact (RHI) events demonstrated strong positive correlations with the timing of SLR and MLR peaks. Cumulative RHI events also negatively correlated with peak MLR amplitude and response gain at frequencies above 5 Hz. Our results provide evidence of a progressive vestibular impairment in combat sports athletes, potentially resulting from blows to the head accumulated in sparring practice and competitive bouts throughout their careers. Taken together, EVS-based vestibular assessments may provide a valuable clinical diagnostic tool and help better inform "return-to-play" and career-length decisions for not only combat sports athletes, but potentially other populations at risk of RHIs.

Capillary, Film, and Vapor Flow in Transient Bare Soil Evaporation (1): Identifiability Analysis of Hydraulic Conductivity in the Medium to Dry Moisture Range

AbstractEvaporation experiments are frequently used to determine soil hydraulic properties. We simulated laboratory evaporation experiments with a coupled water, vapor, and heat flow model which includes the surface energy balance. The simulations are performed with different parametrizations of soil hydraulic properties with a focus on soil hydraulic conductivity in medium to dry soil. In previous studies, conductivity in this moisture range has been shown to be influenced not only by water flow in completely filled capillaries (“capillary flow”) but also by film and corner flow (“film flow”). Our forward simulations highlight the strong influence of an increased conductivity caused by film flow on evaporation rate, cumulative water loss, soil temperature, and soil water pressure head during evaporation. Film flow extends the duration of stage‐1 evaporation and increases the evaporation rate during stage‐2 even if all other physical material properties are the same. The simulated data were used in inverse simulations with the Richards equation to test whether soil hydraulic properties can be identified without bias. This is a priori questionable because the Richards equation is an isothermal flow model and simplifies the true physics considerably, by ignoring thermal liquid and thermal vapor fluxes, as well as temperature effects on the hydraulic properties. Our results show that the identification of the water retention and hydraulic conductivity curves is bias‐free for media with and without film flow. We conclude that the Richards equation can be safely used to identify hydraulic properties from evaporation experiments by inverse modeling.

Subconcussive Head Impacts and Neurocognitive Function Over 3 Seasons of Youth Football.

To determine the association between repetitive subconcussive head impacts and neurobehavioral outcomes in youth tackle football players. Using helmet-based sensors, we measured head impacts for 3 consecutive seasons of play in 29 male players age 9-11. Cumulative impact g's were calculated. Players completed a battery of outcome measures before and after each season, including neuropsychological testing, vestibular-ocular sensitivity, and self- and parent-reported measures of symptoms and attention-deficit hyperactivity disorder (ADHD). Average cumulative impact over 3 seasons was 13 900g. High-intensity hits predicted worse change for self-reported social adjustment (P = .001). Cumulative impact did not predict change in any of the outcome measures. History of ADHD, anxiety, and depression predicted worse change for self-reported symptoms and social adjustment, independent of head impacts. When players were stratified into 3 groups based on cumulative impact across all 3 seasons, differences in outcome measures existed prior to the start of the first season. These differences did not further increase over the course of the 3 seasons. Over 3 consecutive seasons of youth tackle football, we found no association between cumulative head impacts and neurobehavioral outcomes. Larger sample sizes and longer follow-up times would further assist in characterizing this relationship.

Disparate Associations of Years of Football Participation and a Metric of Head Impact Exposure with Neurobehavioral Outcomes in Former Collegiate Football Players.

Years of sport participation (YoP) is conventionally used to estimate cumulative repetitive head impacts (RHI) experienced by contact sport athletes. The relationship of this measure to other estimates of head impact exposure and the potential associations of these measures with neurobehavioral functioning are unknown. We investigated the association between YoP and the Head Impact Exposure Estimate (HIEE), and whether associations between the two estimates of exposure and neurobehavioral functioning varied. Former American football players (N = 58; age = 37.9 ± 1.5 years) completed in-person evaluations approximately 15 years following sport discontinuation. Assessments consisted of neuropsychological assessment and structured interviews of head impact history (i.e., HIEE). General linear models were fit to test the association between YoP and the HIEE, and their associations with neurobehavioral outcomes. YoP was weakly correlated with the HIEE, p = .005, R2 = .13. Higher YoP was associated with worse performance on the Symbol Digit Modalities Test, p = .004, R2 = .14, and Trail Making Test-B, p = .001, R2 = .18. The HIEE was associated with worse performance on the Delayed Recall trial of the Hopkins Verbal Learning Test-Revised, p = .020, R2 = .09, self-reported cognitive difficulties (Neuro-QoL Cognitive Function), p = .011, R2 = .10, psychological distress (Brief Symptom Inventory-18), p = .018, R2 = .10, and behavioral regulation (Behavior Rating Inventory of Executive Function for Adults), p = .017, R2 = .10. YoP was marginally associated with the HIEE, a comprehensive estimate of head impacts sustained over a career. Associations between each exposure estimate and neurobehavioral functioning outcomes differed. Findings have meaningful implications for efforts to accurately quantify the risk of adverse long-term neurobehavioral outcomes potentially associated with RHI.

Reduced wear in vitamin E-infused highly cross-linked polyethylene cups: 5-year results of a randomized controlled trial

Background and purpose — Vitamin E-infused polyethylene is a relatively new material in joint arthroplasty; there are no long-term reports, and only few mid-term results. Using radiostereometric analysis (RSA), we primarily determined whether vitamin E-infused highly cross-linked polyethylene (HXLPE/VitE) acetabular cups show less wear than ultra-high molecular weight polyethylene (UHMWPE) acetabular cups at 5 years after total hip arthroplasty (THA). We also assessed whether wear rates correlate with increasing cup inclination angles or cup sizes. Patients and methods — This is a 5-year follow-up of our previously reported randomized controlled trial of 62 patients with 3 years’ follow-up, who received THA with either an HXLPE/VitE or a UHMWPE acetabular cup. At 5 years, 40 patients were analyzed (22 in the HXLPE/VitE and 18 in the UHMWPE group). Results — HXLPE/VitE cups continued to show less cumulative femoral head penetration than UHMWPE cups (HXLPE/VitE: 0.24 mm, UHMWPE: 0.45 mm; p < 0.001). Distribution of wear was also more even with HXLPE/VitE cups than with UHMWPE cups (p = 0.002). Moreover, the difference in PE wear between 1 and 5 years in both groups showed no statistically significant correlation with increasing cup inclination angles or cup sizes. Finally, no osteolysis and implant loosening occurred, and no revision surgeries were required. Interpretation — Wear rates continue to be lower in HXLPE/VitE cups than in UHMWPE cups at 5 years of follow-up without correlation with increasing cup inclination angles or cup sizes. Finally, HXLPE/VitE cups may have the potential to prevent osteolysis and implant loosening.

Chronic alcohol exposure differentially modulates structural and functional properties of amygdala: A cross‐sectional study

AbstractAnimal models have shown that chronic alcohol exposure is associated with persistent neuroadaptations in amygdala synaptic function, whereas human studies have consistently reported amygdala grey‐matter volume (GMV) reductions in alcohol dependent patients (ADP). We hypothesised that chronic alcohol use associated with neuroadaptations may entail a reconfiguration of the amygdala's functional interactions and that these mechanisms may be affected by structural atrophy. We compared amygdala resting state functional connectivity (RSFC) using a whole brain seed‐based approach and amygdala GMV in abstinent ADP (n = 20) and healthy controls (HC; n = 39), balanced for age, gender and levels of head motion. The potential moderating influence of age, cumulative alcohol exposure, abstinence length and head motion was further examined in the two groups separately using correlational analyses. We found increased amygdala RSFC with substantia nigra/ventral tegmental area (SN/VTA) in ADP compared with HC. As expected, amygdala GMV was lower in ADP. Multiple regression analyses of the ADP group showed that amygdala‐SN/VTA RSFC increases were primarily associated with cumulative alcohol exposure rather than age, whereas amygdala GMV reductions were primarily associated with age rather than cumulative alcohol exposure. The same association between age and amygdala GMV was not observed amongst HC. Importantly, amygdala GMV and amygdala‐SN/VTA RSFC were uncorrelated in ADP, and neither measure was correlated with abstinence length. These results suggest that chronic alcohol exposure is associated with persistent elevations in amygdala‐SN/VTA RSFC and accelerated age‐related grey‐matter atrophy through potentially distinct mechanisms.

Chronic traumatic encephalopathy associated with cumulative soccer heading exposure: A review of the recent literature

Chronic traumatic encephalopathy associated with cumulative soccer heading exposure: A review of the recent literature

Subconcussive head impact exposure between drill intensities in U.S. high school football.

USA Football established five levels-of-contact to guide the intensity of high school football practices. The objective of this study was to examine head impact frequency and magnitude by levels-of-contact to determine which drills had the greatest head impact exposure. Our primary hypothesis was that there would be an incremental increase in season-long head impact exposure between levels-of-contact: air<bags<control<thud<live. This observational study included 24 high-school football players during all 46 practices, 1 scrimmage, 9 junior varsity and 10 varsity games in the 2019 season. Players wore a sensor-installed mouthguard that monitored head impact frequency, peak linear acceleration (PLA), and rotational acceleration (PRA). Practice/game drills were filmed and categorized into five levels-of-contact (air, bags, control, thud, live), and head impact data were assigned into one of five levels-of-contact. Player position was categorized into lineman, hybrid, and skill. A total of 6016 head impacts were recorded during 5 levels-of-contact throughout the season. In the overall sample, total number of impacts, sum of PLA, and PRA per player increased in a near incremental manner (air<bags<control = thud<live), where live drills had significantly higher cumulative frequency (113.7±17.8 hits/player) and magnitude [2,657.6±432.0 g (PLA), and 233.9 ± 40.1 krad/s2 (PRA)] than any other levels-of-contact, whereas air drills showed the lowest cumulative frequency (7.7±1.9 hits/player) and magnitude [176.9±42.5 g (PLA), PRA 16.7±4.2 krad/s2 (PRA)]. There was no significant position group difference in cumulative head impact frequency and magnitude in a season. Although there was no difference in average head impact magnitude across five levels-of-contact and by position group PLA (18.2-23.2g) and PRA (1.6-2.3krad/s2) per impact], high magnitude (60-100g and >100g) head impacts were more frequently observed during live and thud drills. Level-of-contact influences cumulative head impact frequency and magnitude in high-school football, with players incurring frequent, high magnitude head impacts during live, thud, and control. It is important to consider level-of-contact to refine clinical exposure guidelines to minimize head impact burden in high-school football.

Age Of First Exposure Influences Cerebrovascular Reactivity In High School Football Athletes

Late-life physiological and clinical impairments are associated with age of first exposure (AFE) to tackle football. There is a dearth of literature describing how AFE may influence physiological outcomes in current high school football athletes. Cerebrovascular reactivity (CVR) measures the cerebral blood flow response to variations in carbon dioxide partial pressures. Understanding how AFE affects cerebrovascular function in high school athletes may offer insight into potential long-term deficits following cumulative head impact exposure. PURPOSE: To investigate how the age at which high school football athletes began playing tackle football influences baseline CVR. METHODS: High school football athletes [n=29; age=15.8 ± 1.1 yrs; height=175.8 ± 8.1cm; mass=75.1 ± 12.6kg] self-reported AFE (median AFE=13 years old, range=5-15). Transcranial Doppler (TCD) ultrasound was used to assess middle cerebral artery velocity (MCAv) prior to beginning the competitive season. Baseline MCAv was collected for 2 minutes. Changes in MCAv were measured in response to 5 breath-holding trials (20s breath-hold/40s rest) and 5 hyperventilation trials (20s hyperventilation/40s rest). We employed separate mixed effects models with quadratic mean structures to assess group differences in MCAv response to breath-holding and hyperventilation tasks. RESULTS: The AFE significantly predicted CVR during breath-holding (F1,1709=5.27, p=0.02) and hyperventilation (F1,1709=4.08, p=0.04). One-year increases in AFE were associated with a 0.69% reduction in average CVR response during breath-holding and a 0.58% increase in average CVR during hyperventilation. CONCLUSIONS: Though AFE is associated with CVR in high school football players, the underlying mechanisms driving the observed results are unclear. The effect of cumulative head impact exposure at the high school level is understudied despite long-term neurophysiological deficits reported in retired professional football players. Studying neurophysiological responses in young football players may provide important insights into addressing cerebrovascular function and other late-life physiological health in athletes.

Head Impact Burden Differs Between Seasons in Youth and High School US Football Players.

Retrospective estimates of head impact burden in contact sports are often used in studies assessing for correlation of head impact exposure with neurocognitive outcomes later in life. These estimations assume a consistent impact burden from year to year. We monitored head impacts in youth tackle football players in the 6th-8th grades and high school varsity players using helmet-based sensors during two consecutive seasons. Helmet-based pressure sensors were used to measure head impacts, and estimates of peak linear acceleration (g's) were then grouped and summed for cumulative impact. After each season, players estimated whether they experienced an average, below average, or above average head impact burden in relation to their teammates. Of the 98 players who participated, 54 played in both seasons and sustained a median of 102.5 impacts (2206 cumulative g's) in season 1 and 161 impacts (3682 cumulative g's) in season 2. Using pairwise comparisons, number of impacts and cumulative g's increased in the youth players from season 1 to season 2 (p = 0.0021 and p = 0.0018, respectively), but there was a trend towards a decrease in number of impacts and g's at the high school level. In an exploratory analysis, perceived cumulative head impact and measured cumulative g's weakly correlated (Pearson's correlation coefficient = 0.26 for season 1 and 0.02 for season 2). In conclusion, cumulative head impacts differ significantly from one season to the next, and players have difficulty estimating their cumulative head impacts in relation to their team mates, especially at the youth level. Retrospective estimations of head impact burden should account for this variability.

Association of Professional Football Cumulative Head Impact Index Scores With All-Cause Mortality Among National Football League Players

Long-term adverse health outcomes, particularly those associated with repetitive head impacts, are of growing concern among US-style football players in the US and Canada. To assess whether exposure to repetitive head impacts during a professional football career is associated with an increase in the risk of all-cause mortality. This retrospective cohort study included 13 912 players in the 1969 to 2017 National Football League (NFL) seasons. All cause-mortality up until July 1, 2018, was included. Data collection was performed from July 13, 2017, to July 1, 2018, as reported in the Pro Football Reference. The main exposure was a professional football cumulative head impact index (pfCHII). The pfCHII was measured by combining cumulative padded practice time and games played summed during seasons of play reported in the Pro Football Reference and a player position risk adjustment from helmet accelerometer studies. Demographic characteristics except for the pfCHII were calculated for 14 366 players with complete follow-up. The pfCHII was calculated for 13 912 players (eliminating the 454 specials teams players). Cox proportional hazards regression was used to compare hazard ratios (HRs) of death by repetitive head impacts. Analyses were unadjusted and adjusted for birth year, body mass index, and height. Among 14 366 NFL players who had follow-up for analysis, the mean (SD) age was 47.3 (14.8) years, the mean (SD) body mass index was 29.6 (3.9), and 763 of 14 366 players (5.3%) had died. Among 13 912 players in the pfCHII analysis, the median pfCHII was 32.63 (interquartile range, 13.71-66.12). A 1-log increase in pfCHII was significantly associated with an increased hazard of death for the 1969 to 2017 seasons (HR, 2.02; 95% CI, 1.21-3.37; P = .01) after adjustment. The quadratic pfCHII was also statistically significant (HR, 0.91; 95% CI, 0.85-0.98; P = .01), indicating that the hazard of death increased at a decreasing rate, whereas the pfCHII increased. The findings suggest that an increase in repetitive head impacts is associated with an increased hazard of death among NFL players. Reduction in repetitive head impacts from playing football or other activities through additional rule and equipment changes may be associated with reduced mortality.

A Dose Relationship Between Brain Functional Connectivity and Cumulative Head Impact Exposure in Collegiate Water Polo Players.

A growing body of evidence suggests that chronic, sport-related head impact exposure can impair brain functional integration and brain structure and function. Evidence of a robust inverse relationship between the frequency and magnitude of repeated head impacts and disturbed brain network function is needed to strengthen an argument for causality. In pursuing such a relationship, we used cap-worn inertial sensors to measure the frequency and magnitude of head impacts sustained by eighteen intercollegiate water polo athletes monitored over a single season of play. Participants were evaluated before and after the season using computerized cognitive tests of inhibitory control and resting electroencephalography. Greater head impact exposure was associated with increased phase synchrony [r(16) > 0.626, p < 0.03 corrected], global efficiency [r(16) > 0.601, p < 0.04 corrected], and mean clustering coefficient [r(16) > 0.625, p < 0.03 corrected] in the functional networks formed by slow-wave (delta, theta) oscillations. Head impact exposure was not associated with changes in performance on the inhibitory control tasks. However, those with the greatest impact exposure showed an association between changes in resting-state connectivity and a dissociation between performance on the tasks after the season [r(16) = 0.481, p = 0.043] that could also be attributed to increased slow-wave synchrony [F(4, 135) = 113.546, p < 0.001]. Collectively, our results suggest that athletes sustaining the greatest head impact exposure exhibited changes in whole-brain functional connectivity that were associated with altered information processing and inhibitory control.