Head Impact Exposure and Mechanisms in Female High School Lacrosse via an Instrumented Mouthguard

ObjectiveTo quantify the head impact biomechanics, by impact mechanism, of female high school lacrosse players during games using an instrumented mouthguard.BackgroundThere is growing concern for the neurologic effects of repetitive head impacts in sports, which have been linked with several short-term neurophysiologic deficits. Girls' lacrosse represents a popular but understudied sport with regard to head impact exposure and current debate exists as to the need for enhanced protective equipment.Design/MethodsA female high school varsity lacrosse team wore the Stanford Instrumented Mouthguard during competitive games for the 2019 season. Video footage was reviewed to confirm head impact events and remove false-positive recordings. For each impact event, the mechanism was coded as stick contact, player contact, fall, or ball contact. Head impact rates were calculated per athlete exposure (AE, defined as a single player participating in a single game).ResultsSensor data were recorded for 15 female varsity lacrosse players for 14 games and 97 AEs. During games, 31 sensor-recorded head impacts were video-confirmed resulting in a pooled average head impact rate of 0.32 impacts/AE. The video-confirmed impacts were distributed between stick contact (17, 54.8%), player contact (12, 38.7%), and falls (2, 6.5%). There were no ball impacts. Overall peak kinematics were 34.0 ± 26.6 g, 12.0 ± 9.1 rad/s, and 3,666.5 ± 2,987.6 rad/s2. Stick contacts had the highest peak linear acceleration (42.7 ± 32.2 g), angular velocity (14.5 ± 11.1 rad/s), and angular acceleration (4,242.4 ± 3,634.9 rad/s2).ConclusionsStick impacts were the most common impact mechanism and resulted in the highest peak linear and angular kinematics, which may help explain why they are the most common cause of head injury in female lacrosse. By quantifying the head impact exposure, kinematics and mechanisms in female high school lacrosse, targeted injury preventions can be developed, such as rule changes and protective equipment.

The Influence of Headform/Helmet Friction on Head Impact Biomechanics in Oblique Impacts at Different Tangential Velocities

Oblique impacts of the helmet against the ground are the most frequent scenarios in real-world motorcycle crashes. The combination of two factors that largely affect the results of oblique impact tests are discussed in this work. This study aims to quantify the effect of the friction at the interface between the headform and the interior of a motorcycle helmet at different magnitudes of tangential velocity. The helmeted headform, with low friction and high friction surface of the headform, was dropped against three oblique anvils at different impact velocities resulting in three different magnitudes of the tangential velocity (3.27 m/s, 5.66 m/s, 8.08 m/s) with the same normal component of the impact velocity (5.66 m/s). Three impact directions (front, left-side and right-side) and three repetitions per impact condition were tested resulting in 54 impacts. Tangential velocity variation showed little effect on the linear acceleration results. On the contrary, the rotational results showed that the effect of the headform’s surface depends on the magnitude of the tangential velocity and on the impact direction. These results indicate that a combination of low friction with low tangential velocities may result into underprediction of the rotational headform variables that would not be representative of real-world conditions.

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, 5.69 g; 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 3.78 g 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.

Analysis of Head Impact Biomechanics in Youth Female Soccer Players Following the Get aHEAD Safely in Soccer™ Heading Intervention

The effects of repetitive head impacts associated with soccer heading, especially in the youth population, are unknown. The purpose of this study was to examine balance, neurocognitive function, and head impact biomechanics after an acute bout of heading before and after the Get aHEAD Safely in Soccer™ program intervention. Twelve youth female soccer players wore a Triax SIM-G head impact sensor during two bouts of heading, using a lightweight soccer ball, one before and one after completion of the Get aHEAD Safely in Soccer™ program intervention. Participants completed balance (BESS and SWAY) and neurocognitive function (ImPACT) tests at baseline and after each bout of heading. There were no significant changes in head impact biomechanics, BESS, or ImPACT scores pre- to post-season. Deficits in three of the five SWAY positions were observed from baseline to post-season. Although we expected to see beneficial changes in head impact biomechanics following the intervention, the coaches and researchers observed an improvement in heading technique/form. Lightweight soccer balls would be a beneficial addition to header drills during training as they are safe and help build confidence in youth soccer players.

Effects of Boundary Conditions on the Stress Relaxation of Passively Compressed Skeletal Muscle

Computational models of skeletal muscle are useful to study impact biomechanics and surgical-planning. However, the accuracy of these models comes into question as the behavior of muscle in compression is not well understood, specifically in regard to boundary conditions. In this study, we aim to understand how skeletal muscle behaves in different formsof compression (confined and unconfined) at different strain rates. Data from this study will help to develop physiologicallyaccurate computational models of skeletal muscle.

Comparison of Human Surrogate Responses in Underbody Blast Loading Conditions

Impact biomechanics research in occupant safety predominantly focuses on the effects of loads applied to human subjects during automotive collisions. Characterization of the biomechanical response under such loading conditions is an active and important area of investigation. However, critical knowledge gaps remain in our understanding of human biomechanical response and injury tolerance under vertically accelerated loading conditions experienced due to underbody blast (UBB) events. This knowledge gap is reflected in anthropomorphic test devices (ATDs) used to assess occupant safety. Experiments are needed to characterize biomechanical response under UBB relevant loading conditions. Matched pair experiments in which an existing ATD is evaluated in the same conditions as a post mortem human subject (PMHS) may be utilized to evaluate biofidelity and injury prediction capabilities, as well as ATD durability, under vertical loading. To characterize whole body response in the vertical direction, six whole body PMHS tests were completed under two vertical loading conditions. A series of 50th percentile hybrid III ATD tests were completed under the same conditions. Ability of the hybrid III to represent the PMHS response was evaluated using a standard evaluation metric. Tibial accelerations were comparable in both response shape and magnitude, while other sensor locations had large variations in response. Posttest inspection of the hybrid III revealed damage to the pelvis foam and skin, which resulted in large variations in pelvis response. This work provides an initial characterization of the response of the seated hybrid III ATD and PMHS under high rate vertical accelerative loading.

THE EFFECT OF A BODY CHECKING RULE CHANGE ON HEAD IMPACT BIOMECHANICS IN BANTAM ICE HOCKEY ATHLETES

Background: Body checking is the most common injury mechanism in ice hockey. Rule changes have sought to mitigate body checking exposure among youth players. In 2011, USA Hockey changed the legal body checking age from Pee Wee (11/12-year-olds) to Bantam (13/14-year-olds). Interestingly, Bantam players with checking experience during Pee Wee had a lower concussion risk relative to Bantam players without checking experience in a sample of Canadian youth hockey players. Understanding the head impact biomechanics underlying these findings could further elucidate the consequences of this rule change. Purpose: To determine the association between Pee Wee checking exposure and head impact biomechanics in a cohort of Bantam players. Methods: We prospectively collected data on Bantam ice hockey players during the 2006/07-2009/10 seasons and the 2012-2013 season. The 2006/07-2009/10 cohort (n= 61, age=13.9±0.5 years, height=168.2±8.7 cm, mass=59.9±10.4 kg) was allowed to body check (BC) as a Pee Wee player. The 2012-2013 cohort (n=15, age=13.3±0.4 years, height=167.5±7.4 cm, mass=57.5±8.6 kg) was not permitted to body check (NBC) as a Pee Wee player. Over the course of each season, head impacts were measured using in-helmet accelerometers. Only head impacts with linear acceleration ≥10 g were included in our analysis. Main outcome measures were mean linear acceleration (g) and rotational acceleration (rad/s2). Levene’s tests assessed equality of variance between groups. We employed mixed effects models to assess group differences in mean linear and rotational acceleration between BC and NBC groups. Results: The BC and NBC groups did not differ in height (t74=0.28, p=0.78) or mass (t74=0.84, p=0.40). When assessing group differences in head impact biomechanics, the NBC experienced significantly greater linear acceleration (F1,74=4.36, p=0.04) and greater rotational acceleration (F1,74=21.2, p<0.001) relative to the BC group. On average, the NBC group experienced 23.1 ± 0.87 g linear acceleration and 1993.5 ± 68.4 rad/s2 rotational acceleration compared to the BC group, which experienced 21.2 ± 0.30 g linear acceleration and 1615.9 ± 45.2 rad/s2 rotational acceleration. Conclusions: Bantam ice hockey players without body checking experience during their Pee Wee years experienced greater average linear and rotational acceleration relative to players with Pee Wee body checking experience. While removing body checking from Pee Wee ice hockey may reduce short-term injury risk, these athletes may demonstrate more high-risk head impact biomechanics when legally allowed to body check. Future research should continue to examine the influence of policy changes on head impact biomechanics and injury risk in youth ice hockey. [Figure: see text]