Rotational Head Kinematics in Football Impacts: An Injury Risk Function for Concussion

Proper evaluation of ski helmet designs and safety standards should rely on head impact conditions involved in skiing and snowboarding head injuries. To study these impacts, main crash scenarios involving head injuries are numerically replicated. Multibody models of skiers and snowboarders were developed to investigate five common crash scenarios involved in traumatic brain injury: forward and sideways skiing falls, snowboarding backward falls, collisions between users and collisions with obstacles. For each scenario, the influence of crash conditions on head impact (location, speed, linear and rotational accelerations) and risk of injury are evaluated. Crash conditions were initial velocity, user height, position and approach angle, slope steepness, obstacles, and snow stiffness. One thousand one hundred forty-nine crashes were simulated and three significant levels of impact conditions were discriminated over the investigated crash scenarios: 1) the smallest normal-to-slope impact velocities (6 km·h; 22 km·h) and peak linear accelerations (42g; 75g) were obtained during forward and sideways skiing falls; 2) snowboarding backward falls and collisions between users were associated with high normal-to-surface impact velocities (26 km·h; 32 km·h) and head accelerations (80g; 149g) above one published threshold for mild traumatic brain injury but below the pass/fail criteria of helmet standard tests; 3) collisions with obstacles were associated with high normal-to-surface impact velocities (19 km·h; 35 km·h) and the highest head accelerations (626g; 1885g). Current impact conditions of helmet standard evaluations consistently replicate collisions with obstacles, but need to be revised to better reflect other significant crash scenarios leading to traumatic brain injury.

Future Advances and Areas of Future Focus in the Treatment of Sport-Related Concussion

<div class="section abstract"><div class="htmlview paragraph">Recent studies have investigated head injury metrics, including mild traumatic brain injury (mTBI), or concussion risks, in low- to moderate-speed rear-end collisions, with linear and angular head accelerations contributing to the risk of developing a concussion. The present study analyzes head acceleration values in rear-end collisions at an impact severity of 5–30 km/h delta-V. Biomechanical data was obtained from HIII 50th percentile male anthropomorphic test devices (ATDs) seated in the target subject vehicles and utilizing safety restraints and head rests. Concussion risks were calculated from resultant linear and angular head accelerations recorded in the ATDs, and a linear regression model was used to determine what, if any, relationship existed between these head injury metrics and impact severity. The results indicate that there is a significant and positive relationship between head acceleration metrics and impact severity, particularly in the sagittal plane, with F-values < 0.05. Additionally, there is a positive relationship between concussion risks and impact severity, but results also determine that the concussion risks are less than 0.1% and indistinguishable from 0 at this range of impact severity. An outlier test that included head impact with a rear-seated passenger ATD yielded a less than 2% risk of sustaining a concussion. It is expected that the results of this study will aid in accident reconstruction and biomechanical analysis for restrained occupants involved in low- to moderate-speed rear-end collisions.</div></div>

Abstract:Sport-related concussion (SRC) is a common injury in recreational and organized sport. Over the past 30 years, there has been significant progress in our scientific understanding of SRC, which in turn has driven the development of clinical guidelines for diagnosis, assessment, and managemen

Objectives: This study sought to measure the head accelerations induced from upper extremity to head and head to head impact during the game of football and relate this to the...

Sport-related concussion (SRC) is a common and complex injury in athletic populations. Linear head acceleration (LHA) and rotational head acceleration (RHA) are key biomechanical factors believed to contribute to SRC, each through distinct mechanisms. Evaluating head impact magnitudes across different sports, athlete populations, and measurement methods is essential for advancing SRC injury prevention and risk assessment. We aimed to examine linear and rotational head acceleration magnitudes associated with SRC impacts in athletes participating in team sports across all ages and both sexes. We conducted a systematic review and meta-analysis adhering to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. We searched three databases (MEDLINE, Scopus, SPORTDiscus) until 4 September, 2024, and the literature search was updated on the 10 November, 2025. Observational and experimental studies reporting peak LHA and/or RHA during SRC impacts in team sport athletes were included. Data were extracted on study characteristics, instrumentation, and head impact magnitudes. The risk of bias was assessed using the National Institutes of Health Quality Assessment Tool, and the certainty of the evidence was evaluated using GRADE. Random-effects meta-analyses were conducted to compare SRC and non-concussive impacts, and subgroup analyses were performed by sport type, age group, sex, session type, and instrumentation type, reporting standardized mean difference and mean difference. Between-group differences were assessed using Qb statistics, and heterogeneity was evaluated using the I2 statistics. Sensitivity and publication bias analyses were also performed. Data from 30 articles representing 3262 athletes (12% female) were included. Sport-related concussion impacts produced significantly greater head acceleration magnitudes than non-concussive impacts, with large differences for both LHA (69.6g vs 25.3g; standardized mean difference = 2.42; 95% confidence interval 1.73-3.12) and RHA (4931rad/s2 vs. 1966rad/s2; standardized mean difference = 1.99; 95% confidence interval 1.17-2.81). For SRC impacts, subgroup analyses revealed significant differences across sports (p < 0.001), age groups (LHA only, p = 0.01), sexes (LHA only, p < 0.001), and instrumentation types (LHA p < 0.001; RHA p = 0.02). The highest LHA values were observed in American Football (83.2g), while the highest RHA values were recorded in rugby (7627rad/s2). Higher LHA values were recorded for male athletes (78.2g) compared with female athletes (44.2g), and for high school athletes (88.3g) compared with youth (61.4g) and adult athletes (72.2g). Helmet-mounted sensors recorded the highest LHA (79.0g), and skin patches recorded the highest RHA (6938rad/s2). No significant differences were found between games and practices. In team sports, SRC impacts are associated with significantly higher LHA and RHA than non-concussive impacts. The observed overlap and contextual variability in head acceleration magnitudes highlight the importance of considering individual-specific and context-specific interpretation in SRC risk assessment and provide a foundation for improving head impact monitoring, injury prevention strategies, and athlete safety. PROSPERO CRD42024584070.

&lt;div class="htmlview paragraph"&gt;This study explores the dynamics of head and cervical spine impact with the specific goals of determining the effects of head inertia and impact surface on injury risk. Head impact experiments were performed using unembalmed head and neck specimens from 22 cadavers. These included impacts onto compliant and a rigid surfaces with the surface oriented to produce both flexion and extension attitudes. Tests were conducted using a drop track system to produce impact velocities on the order of 3.2 m/s. Multiaxis transduction recorded the head impact forces, head accelerations, and the reactions at T1. The tests were also imaged at 1000 frames/sec.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;Injuries occurred 2 to 30 msec following head impact and prior to significant head motion. Head motions were not found to correlate with injury classification. Decoupling was observed between the head and T1, resulting in a lag in the force histories. Cervical spine loading due to head rebound constituted up to 54±16 percent of the total axial neck load for padded impacts and up to 38±30 percent for the rigid impacts. Dynamic buckling was also observed; including first order modes and transient higher order modes which shifted the structure from a primarily compressive mode of deformation to various bending modes. The average load at failure was 2243±572 N for males and 1061 ± 273 N for females. The difference between male and female tolerance was significant &lt;i&gt;p&lt;/i&gt; = 0.0015). Impacts onto the padded surfaces produced significantly larger neck impulses (&lt;i&gt;p&lt;/i&gt; = 0.00023) and a significantly greater frequency of cervical spine injuries than rigid impacts (&lt;i&gt;p&lt;/i&gt; = 0.043). The impact angle was also correlated with injury risk (&lt;i&gt;p&lt;/i&gt; &amp;lt; 0.00001).&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;These experiments demonstrate that in the absence of head pocketing, the head mass can provide sufficient constraint to cause cervical spine injury. The buckling modes illustrate the kinematic complexity of cervical spine dynamics and may explain why injuries can occur at different vertebral levels and with widely varying mechanism in compressive head impacts. These experiments also suggest that highly deformable padded contact surfaces should be employed carefully in environments where there is the risk for cervical spine injury; however, the orientation of the head, neck, and torso relative to the impact surface is of greater significance.&lt;/div&gt;

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.

Despite increased concern about the health consequences of contact sports, little is known about athletes' understanding of their own risk of sports-related injury. To assess whether college football players accurately estimate their risk of concussion and nonconcussion injury and to identify characteristics of athletes who misestimate their injury risk. In this survey study, questionnaires were given to 296 current college football players on 4 teams from the 3 of the 5 most competitive conferences of the US National Collegiate Athletic Association. Surveys were conducted between February and May 2017. Data were analyzed from June 2017 through July 2020. Multiple approaches were taken to compare athlete perceptions of their risks of concussion and nonconcussion injury with individual probabilities of these risks, which were modeled using logistic regression. Of 296 male college-aged athletes from 4 football teams who participated in the survey, 265 (89%) answered all questions relevant for this study. Participating teams were similar to nonparticipating teams across nearly all measured characteristics. One hundred athletes (34%) had sustained 1 or more concussions, and 197 (68% of the 289 who responded to the question) had sustained 1 or more injuries in the previous football season. Logistic regression models of single-season injury and concussion had reasonably good fit (area under the curve, 0.75 and 0.73, respectively). Of the 265 participants for whom all relevant data were available, 111 (42%) underestimated their risk of concussion (χ2 = 98.6; P = .003). A similar proportion of athletes (113 [43%]) underestimated their risk of injury, although this was not statistically significant (χ2 = 34.0; P = .09). An alternative analytic strategy suggested that 241 athletes (91%) underestimated their risk of injury (Wilcoxon statistic, 7865; P < .001) and 167 (63%) underestimated their risk of concussion (Wilcoxon statistic, 26 768; P < .001). The findings of this survey study suggest that college football players may underestimate their risk of injury and concussion. The implications for informed participation in sport are unclear given that people generally underestimate health risks. It is necessary to consider whether athletes are sufficiently informed and how much risk is acceptable for an athlete to participate in a sport.

OBJECTIVE This study evaluated the frequency, magnitude, and location of head impacts in practice drills within a youth football team to determine how head impact exposure varies among different types of drills. METHODS On-field head impact data were collected from athletes participating in a youth football team for a single season. Each athlete wore a helmet instrumented with a Head Impact Telemetry (HIT) System head acceleration measurement device during all preseason, regular season, and playoff practices. Video was recorded for all practices, and video analysis was performed to verify head impacts and assign each head impact to a specific drill. Eleven drills were identified: dummy/sled tackling, install, special teams, Oklahoma, one-on-one, open-field tackling, passing, position skill work, multiplayer tackle, scrimmage, and tackling drill stations. Generalized linear models were fitted to log-transformed data, and Wald tests were used to assess differences in head accelerations and impact rates. RESULTS A total of 2125 impacts were measured during 30 contact practices in 9 athletes (mean age 11.1 ± 0.6 years, mean mass 44.9 ± 4.1 kg). Open-field tackling had the highest median and 95th percentile linear accelerations (24.7 g and 97.8 g, respectively) and resulted in significantly higher mean head accelerations than several other drills. The multiplayer tackle drill resulted in the highest head impact frequency, with an average of 0.59 impacts per minute per athlete, but the lowest 95th percentile linear accelerations of all drills. The front of the head was the most common impact location for all drills except dummy/sled tackling. CONCLUSIONS Head impact exposure varies significantly in youth football practice drills, with several drills exposing athletes to high-magnitude and/or high-frequency head impacts. These data suggest that further study of practice drills is an important step in developing evidence-based recommendations for modifying or eliminating certain high-intensity drills to reduce head impact exposure and injury risk for all levels of play.

Women’s lacrosse is an ‘incidental contact’ sport meaning that intentional contact with an opponent is not permitted by the game’s rules. Despite this, women’s lacrosse played at the high school and collegiate varsity levels of competition carry a risk of repetitive head impact exposure and sport-related concussion. Head impact exposure at the collegiate club level of women’s lacrosse has not yet been described. PURPOSE: To characterize the anticipated and observed incidence of head impacts in women’s collegiate club lacrosse. METHODS: Experienced women’s collegiate club lacrosse players (n=10) filled out questionnaires reporting how often they sustained head impacts (per game exposure) during the past year. Headband-mounted head impact sensors were worn by athletes (n=11) during eight collegiate club lacrosse games sanctioned by the Western Women’s Lacrosse League. The sensors reported the peak linear acceleration (PLA) and peak rotational acceleration (PRA) associated with each recorded accelerative event. Head impacts were confirmed by two researchers independently reviewing competition video time-synced with sensors. Video review was also used to determine the mechanisms of confirmed impacts. RESULTS: Athletes had a median 4 (range: 0.25 - 8) years of lacrosse experience and expected to sustain a median 0 (range: 0 - 3) head impacts per game. 75 accelerative events were recorded by the head impact sensors across 81 total game exposures. Six head impacts were confirmed using video and 69 accelerative events were rejected as false positives. Confirmed impacts had a median PLA of 21.0 g (range: 18.3 g - 48.3 g) and PRA of 1.1 krad/s2 (range: 0.7 krad/s2 - 5.7 krad/s2). Four impacts resulted from contact with an opponent’s body and two impacts resulted from contact with an opponent’s stick. Only one head impact incurred a penalty against the opposing player. CONCLUSIONS: Athletes anticipate and sustain infrequent head impacts in women’s collegiate club lacrosse relative to lacrosse and contact sports played at the high school and collegiate varsity levels of competition. Those impacts that are sustained are of relatively low magnitude. Head impact sensors are prone to high false positive rates and the use of video recordings to filter sensor data is necessary.

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Petit et al. 2015 and Lebarbé et al. 2016 reported on two studies where the injury mechanism and threshold of the sacroiliac joint were investigated in two slightly oblique crash test conditions from 18 Post Mortem Human Subjects (PMHS) tests. They concluded that the sacroiliac joint fractures were associated with pubic rami fractures. These latter being reported to occur first in the time history. Therefore it was recommended not to define a criterion specific for the sacroiliac joint.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;In 2012, injury risk curves were published for the WorldSID dummy by Petitjean et al. For the pelvis, dummy and PMHS paired tests from six configurations were used (n = 55). All of these configurations were pure lateral impacts. In addition, the sacroiliac joint and femur neck loads were not recorded, and the dummy used was the first production version (WorldSID revision 1). Since that time, the WorldSID was updated several times, including changes in the pelvis area.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;In the present study, the two slightly oblique PMHS test configurations of 2015 and 2016 (n = 18) as well as three of the reference configurations used in the 2012 IRC (n = 43) plus one impactor configuration from WSU (n = 9) were duplicated using the 50th percentile male WorldSID dummy build level F. In these tests, the dummy was systematically equipped with the SI-joint and femur neck load cells.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;The results show that the sacroiliac Fy is a better pelvic ring injury predictor than the pubic load. The aim of the paper is to provide an analysis of the paired test results and to propose both an updated pelvic injury criterion and the injury risk curve (IRC).&lt;/div&gt;&lt;/div&gt;

Falls are commonly used as a false history by caregivers to conceal child abuse. Determining biomechanical compatibility is a key aspect in differentiating abuse from accident. Current forensic approaches are limited in assessing biomechanical compatibility of short-distance falls involving children due to a lack of reliable witnessed falls with known injury outcomes. The goals of this pilot study were to characterize biomechanical measures and to examine differences in biomechanical measures based on child and fall characteristics in reliable witnessed video-recorded falls involving children. The results of this study will serve as preliminary data for an on-going larger study with the aim of improving forensic investigations with a fall history. Children between the ages of 1-3 years in a video monitored childcare center were equipped with a biometric measuring device that collected head accelerations and velocities during falls. Additionally, Head Injury Criteria (HIC) values and impact durations were determined. Video surveillance was used to capture fall dynamics and to provide reliable witnessed falls. For each fall event, whole-body impact biomechanics were determined using fall characteristics, coefficient of restitution measurements, and child anthropometric measurements. The results of the study indicate that fall characteristics had an effect on biomechanical measures. Falls with head impact were associated with greater head accelerations and shorter impact durations and thus, would be associated with an increased likelihood of injury risk compared to falls without head impacts. Head biomechanical measures also increased for falls onto stiffer surfaces than falls onto less stiff surfaces. Falls from height resulted in an increase in whole-body biomechanical measures compared to ground based falls. Fall events that resulted in head impacts with objects prior to impacting the ground were associated with greater biomechanical measures and injury risk than any other falls. However, no injuries requiring medical care occurred to any child and biomechanical measures obtained indicated that there was a low level of injury risk. To our knowledge, this was the first study of video-recorded pediatric falls that included biometric measurement of head biomechanics. Findings from this study address the on-going question as to whether short-distance falls can cause severe or fatal injuries, and can potentially aid forensic investigations in determining if a fall history could account for a child’s presenting injuries. Future work will expand the fall sample size to further advance our understanding of fall biomechanics and injury risk in children.

Accounting for sampling variability, injury under-reporting, and sensor error in concussion injury risk curves

Sports-related concussion is the most common athletic head injury with football having the highest rate among high school athletes. Traditionally, research on the biomechanics of football-related head impact has been focused at the collegiate level. Less research has been performed at the high school level, despite the incidence of concussion among high school football players. The objective of this study is to twofold: to quantify the head impact exposure in high school football, and to develop a cumulative impact analysis method. Head impact exposure was measured by instrumenting the helmets of 40 high school football players with helmet mounted accelerometer arrays to measure linear and rotational acceleration. A total of 16,502 head impacts were collected over the course of the season. Biomechanical data were analyzed by team and by player. The median impact for each player ranged from 15.2 to 27.0 g with an average value of 21.7 (±2.4) g. The 95th percentile impact for each player ranged from 38.8 to 72.9 g with an average value of 56.4 (±10.5) g. Next, an impact exposure metric utilizing concussion injury risk curves was created to quantify cumulative exposure for each participating player over the course of the season. Impacts were weighted according to the associated risk due to linear acceleration and rotational acceleration alone, as well as the combined probability (CP) of injury associated with both. These risks were summed over the course of a season to generate risk weighted cumulative exposure. The impact frequency was found to be greater during games compared to practices with an average number of impacts per session of 15.5 and 9.4, respectively. However, the median cumulative risk weighted exposure based on combined probability was found to be greater for practices vs. games. These data will provide a metric that may be used to better understand the cumulative effects of repetitive head impacts, injury mechanisms, and head impact exposure of athletes in football.