Head Impact Magnitude Research Articles

Individual Impact Magnitude vs. Cumulative Magnitude for Estimating Concussion Odds.

Helmeted impact devices have allowed researchers to investigate the biomechanics of head impacts in vivo. While increased impact magnitude has been associated with greater concussion risk, a definitive concussive threshold has not been established. It is likely that concussion risk is not determined by a single impact itself, but a host of predisposing factors. These factors may include genetics, fatigue, and/or prior head impact exposure. The objective of the current paper is to investigate the association between cumulative head impact magnitude and concussion risk. It is hypothesized that increased cumulative magnitudes will be associated with greater concussion risk. This retrospective analysis included participants that were recruited from regional high-schools in Illinois and Michigan from 2007 to 2014 as part of an ongoing study on concussion biomechanics. Across seven seasons, 185 high school football athletes were instrumented with the Head Impact Telemetry system. Out of 185 athletes, 31 (17%) sustained a concussion, with two athletes sustaining two concussions over the study period, yielding 33 concussive events. The system recorded 78,204 impacts for all concussed players. Linear acceleration, rotational acceleration, and head impact telemetry severity profile (HITsp) magnitudes were summed within five timeframes: the day of injury, three days prior to injury, seven days prior to injury, 30days prior to injury, and prior in-season exposure. Logistic regressions were modeled to explain concussive events based on the singular linear acceleration, rotational acceleration, and HITsp event along with the calculated summations over time. Linear acceleration, rotational acceleration, and HITsp all produced significant models estimating concussion (p<0.05). The strongest estimators of a concussive impact were the linear acceleration (OR=1.040, p<0.05), rotational acceleration (OR=1.001, p<0.05), and HITsp (OR=1.003, p<0.05) for the singular impact rather than any of the cumulative magnitude calculations. Moreover, no cumulative count measure was significant for linear or rotational acceleration. Results from this investigation support the growing literature indicating cumulative magnitude is not related to concussion likelihood. Cumulative magnitude is a simplistic measure of the total exposure sustained by a player over a given period. However, this measure is limited as it assumes the brain is a static structure unable to undergo self-repair. Future research should consider how biological recovery between impacts may influence concussion risk.

Biomechanical head impact characteristics during sparring practice sessions in high school taekwondo athletes.

OBJECTIVE The purpose of this study was to monitor head impact magnitude and characteristics, such as impact location and frequency, at high school taekwondo sparring sessions. METHODS Eight male high school taekwondo athletes participated in this study. The head impact characteristics were recorded by X-Patch, a wireless accelerometer and gyroscope, during 6 taekwondo sparring sessions. The outcome measures were the peak linear acceleration ( g = 9.81 msec2), peak rotational acceleration, rotational velocity, and Head Injury Criterion. RESULTS A total of 689 impacts occurred over 6 sessions involving the 8 athletes. There was an average of 24 impacts per 100 minutes, and there were significant differences in the frequency of impacts among both the sessions and individual athletes. In order of frequency, the most commonly hit locations were the side (38.2%), back (35.7%), and front (23.8%) of the head. CONCLUSIONS The data indicate that there is a relatively high number of head impacts experienced by taekwondo athletes during sparring practice. According to the rotational acceleration predicting impact severity published in previous research, 17.1% of the impacts were deemed to be a moderate and 15.5% were deemed to be severe.

Head Impact Biomechanics in Women's College Soccer.

There are limited nonlaboratory soccer head impact biomechanics data. This is surprising given soccer's global popularity. Epidemiological data suggest that female college soccer players are at a greater concussion injury risk than their male counterparts. Therefore, the purposes of our study were to quantify head impact frequency and magnitude during women's soccer practices and games in the National Collegiate Athletic Association and to characterize these data across event type, playing position, year on the team, and segment of game (first and second halves). Head impact biomechanics were collected from female college soccer players (n = 22; mean ± SD age = 19.1 ± 0.1 yr, height = 168.0 ± 3.5 cm, mass = 63.7 ± 6.0 kg). We employed a helmetless head impact measurement device (X2 Biosystems xPatch) before each competition and practice across a single season. Peak linear and rotational accelerations were categorized based on impact magnitude and subsequently analyzed using appropriate nonparametric analyses. Overall, women's college soccer players experience approximately seven impacts per 90 min of game play. The overwhelming majority (~90%) of all head impacts were categorized into our mildest linear acceleration impact classification (10g-20g). Interestingly, a higher percentage of practice impacts in the 20g-40g range compared with games (11% vs 7%) was observed. Head impact biomechanics studies have provided valuable insights into understanding collision sports and for informing evidence-based rule and policy changes. These have included changing the football kickoff, ice hockey body checking ages, and head-to-head hits in both sports. Given soccer's global popularity, and the growing public concern for the potential long-term neurological implications of collision and contact sports, studying soccer has the potential to impact many athletes and the sports medicine professionals caring for them.

Head Impact Magnitude in American High School Football

Head Impact Magnitude in American High School Football

Laboratory Validation of Two Wearable Sensor Systems for Measuring Head Impact Severity in Football Players.

Wearable sensors can measure head impact frequency and magnitude in football players. Our goal was to quantify the impact detection rate and validity of the direction and peak kinematics of two wearable sensors: a helmet system (HITS) and a mouthguard system (X2). Using a linear impactor, modified Hybrid-III headform and one helmet model, we conducted 16 impacts for each system at 12 helmet sites and 5 speeds (3.6-11.2 m/s) (N = 896 tests). Peak linear and angular accelerations (PLA, PAA), head injury criteria (HIC) and impact directions from each device were compared to reference sensors in the headform. Both sensors detected ~96% of impacts. Median angular errors for impact directions were 34° for HITS and 16° for X2. PLA, PAA and HIC were simultaneously valid at 2 sites for HITS (side, oblique) and one site for X2 (side). At least one kinematic parameter was valid at 2 and 7 other sites for HITS and X2 respectively. Median relative errors for PLA were 7% for HITS and -7% for X2. Although sensor validity may differ for other helmets and headforms, our analyses show that data generated by these two sensors need careful interpretation.

Head Impact Exposure and Neurologic Function of Youth Football Players.

Football players are subjected to repetitive impacts that may lead to brain injury and neurologic dysfunction. Knowledge about head impact exposure (HIE) and consequent neurologic function among youth football players is limited. This study aimed to measure and characterize HIE of youth football players throughout one season and explore associations between HIE and changes in selected clinical measures of neurologic function. Twenty-two youth football players (11-13 yr) wore helmets outfitted with a head impact telemetry (HIT) system to quantify head impact frequency, magnitude, duration, and location. Impact data were collected for each practice (27) and game (9) in a single season. Selected clinical measures of balance, oculomotor performance, reaction time, and self-reported symptoms were assessed before and after the season. The median individual head impacts per practice, per game, and throughout the entire season were 9, 12, and 252, respectively. Approximately 50% of all head impacts (6183) had a linear acceleration between 10g and 20g, but nearly 2% were greater than 80g. Overall, the head impact frequency distributions in this study population were similar in magnitude and location as in high school and collegiate football, but total impact frequency was lower. Individual changes in neurologic function were not associated with cumulative HIE. This study provides a novel examination of HIE and associations with short-term neurologic function in youth football and notably contributes to the limited HIE data currently available for this population. Whereas youth football players can experience remarkably similar head impact forces as high school players, cumulative subconcussive HIE throughout one youth football season may not be detrimental to short-term clinical measures of neurologic function.

Comparison of Head Impact Exposure Measures in Football from Two Different Accelerometry Devices

The Head Impact Telemetry System (HITS) has been used to measure real-time head impact exposure (HIE) in football for the past decade. More recently, several lighter and less expensive head impact sensors have entered the retail market, intended for individual player monitoring of HIE. The ability of these products to accurately measure HIE in the field is largely unknown PURPOSE: To compare measures of HIE in football obtained from the GForce Tracker (GFT), a retail head impact sensor, with those derived simultaneously from HITS. METHODS: Seventeen middle school football players (12-14 yr) wore helmets outfitted concurrently with HITS and GFT during twelve consecutive practices and one game in a season. HITS utilized a six single-axis accelerometer array, whereas GFT used one triaxial accelerometer to measure the frequency, linear acceleration and location of head impacts. RESULTS: Total impacts measured by HITS and GFT were 476 and 3264, respectively. Median head impacts per player were significantly correlated between HITS and GFT (r = 0.77; P < 0.001), but were significantly lower when measured by HITS (28 ± 17 vs. 192 ± 96 impacts/player, respectively)(P < 0.001). The 50th and 95th percentiles of linear acceleration were 21.1g and 55.1g for HITS and 17.8g and 50.5g for GFT. Mean linear acceleration measured by HITS (26.0 ± 14.5g) was significantly greater than that measured by GFT (22.6 ± 13.9g)(P < 0.001). Head impact frequency registered by HITS was highest to the front of the helmet (48%), followed by the back of the helmet (25%), the side of the helmet (15%) and the top of the helmet (11%); whereas GFT measured impacts occurred most frequently to the side of the helmet (33%), followed by the back of the helmet (28%), the front of the helmet (28%) and the top of the helmet (11%). CONCLUSION: This is the first study to compare HIE measured concomitantly with GFT and HITS in football. There were several notable discrepancies in head impact frequency, magnitude and location distribution measured by the two devices that would drastically affect the interpretation of individual player HIE. These findings highlight the need for additional research to determine the on-field validity and practical utility of all sensors used for real-time monitoring of head impacts in football.

B-65 Thematic Poster - Hydration Assessment

Football players experience numerous blows to the head that may increase the risk for brain injury. While the majority of active football players are younger than high school age, investigations of head impact exposure (HIE) among youth players has been limited. Even less is known about the acute effects of HIE on neurological function in this population. PURPOSE: To measure HIE in youth football players over a full season and explore associations between HIE and changes in selected clinical measures of neurological function. METHODS: Twenty-two male middle school football players (11-14 yr) wore helmets outfitted with a Head Impact Telemetry System that uses six single-axis accelerometers to track and quantify head impact frequency, magnitude, duration and location. Impact data were collected for each practice and game during the season (27 practices, 9 games). Selected clinical measures of balance (BAL; AMTI force plate, NeuroCom Balance Master), oculomotor performance (OP; King-Devick Test), and simple reaction time (RT) were also assessed before (PRE) and after (POST) the season. RESULTS: The median number of head impacts per player was 252 (season), 80 (games) and 144 (practices), respectively. The maximum number of head impacts sustained by a single player was 880 for the entire season and 54 for a single session (practice). Approximately 48.8% of all head impacts had a linear acceleration between 10-20 g, 49.5% were between 21-80 g and 1.7% were greater than 80 g. Nearly all BAL, OP and RT measures were unchanged (P = 0.065 - 0.648 [BAL]; P = 0.079 - 0.221 [OP]; P = 0.346 [RT]) at POST. There were no POST deficits in any of the measures evaluated. CONCLUSIONS: This is the first study to examine associations between HIE and clinical measures of neurological function in middle school football players. Overall HIE in these players was found to be intermediate to what has been reported for younger and older (high school) players. Furthermore, these data suggest that the primary difference in HIE between middle school and high school football players is impact frequency. With no observed impairments in selected clinical measures of neurological function or a discernable relation between HIE and post-season deficits, an acute adverse effect of playing football on neurological function cannot be confirmed in this population.

Subconcussive Head Impact Biomechanics

Recent literature suggests that subconcussive impacts may influence cognitive functioning across the life span. These effects are suggested to manifest as functional and possibly structural changes. Head impact biomechanics during American football have been characterized from the high school to professional level, but style of play has not been considered. The aim of this investigation was to quantify and compare head impact frequencies and magnitudes between two different offensive schemes. We investigated the frequencies and magnitudes (linear acceleration [g], rotational acceleration [rad·s], and HITsp) of head impacts sustained by 83 high school football athletes, playing for schools using two different offensive schemes. The two schemes comprised a run-first offense (42 athletes) and a pass-first offense (41 athletes). The Head Impact Telemetry System was used to record head impact measures. A total of 35,620 impacts were recorded across two seasons. Athletes in the run-first offense sustained an average of 456 head impacts per season (41 practices and 9 games), whereas the pass-first offense athletes sustained an average of 304 head impacts per season (44 practices and 9 games). The pass-first offense, however, sustained significantly higher impact magnitudes (P values < 0.05; 28.56g, 1777.58 rad·s, and 16.24) than the run-first offense (25.67g, 1675.36 rad·s, and 15.48) across a season. These data provide a first look at how different offensive strategies may influence head impact exposure in football athletes. In the study population, a run-first offense was associated with more frequent head impacts, of smaller magnitude, than a pass-first offense.

Head Impact Exposure and Magnitude in High School Football by Player Position (IN5-1.004)

Head Impact Exposure and Magnitude in High School Football by Player Position (IN5-1.004)

Head Impact Exposure and Magnitude in High School Football by Player Position (P01.266)

Head Impact Exposure and Magnitude in High School Football by Player Position (P01.266)

The Effect of Play Type and Collision Closing Distance on Head Impact Biomechanics

Football accounts for 55% of concussions to collegiate athletes. In the National Football League, players are at a greater risk for concussion during kickoffs and punts compared to rushing and passing plays. The two primary purposes of this study were to determine if game-related special teams head impacts were greater in magnitude than head impacts sustained during offensive and defensive plays, and to better understand the effect closing distance between players (short vs. long) had on head impact magnitude. Collegiate football players were enrolled in a prospective cohort study assessing head impact biomechanics during special teams, offensive, and defensive collisions; long closing distance (≥ 10 yards) and short closing distance (<10 yards) impacts were also studied. Data were analyzed using random intercepts general linear mixed models. Long closing distance collisions generated more severe head impacts than short closing distances. Collisions occurring on special teams plays over long closing distances were most severe while collisions occurring on special teams and defensive plays over short closing distances resulted in the least severe impacts. Decreasing the impact severity of collisions in collegiate football may be accomplished by reducing the closing distance prior to impact.

No Evidence for a Cumulative Impact Effect on Concussion Injury Threshold

Recent studies using a helmet-based accelerometer system (Head Impact Telemetry System [HITS]) have demonstrated that concussions result from a wide range of head impact magnitudes. Variability in concussion thresholds has been proposed to result from the cumulative effect of non-concussive head impacts prior to injury. We used the HITS to collect biomechanical data representing >100,000 head impacts in 95 high school football players over 4 years. The cumulative impact histories prior to 20 concussive impacts in 19 athletes were compared to the cumulative impact histories prior to the three largest magnitude non-concussive head impacts in the same athletes. No differences were present in any impact history variable between the concussive and non-concussive high magnitude impacts. These analyses included the number of head impacts, cumulative HIT severity profile value, cumulative linear acceleration, and cumulative rotational acceleration during the same practice or game session, as well as over the 30 min and 1 week preceding these impacts. Our data do not support the proposal that impact volume or intensity influence concussion threshold in high school football athletes.

Characteristics of head impacts sustained by youth ice hockey players

This study aimed to measure the magnitude of head impacts sustained by 14 male, youth (13 years old) ice hockey players wearing instrumented helmets, and to compare impacts across event type (practice, game), player position, and location. Head impact magnitudes were captured during 58 games and 51 practices. Mixed linear models were utilized to analyze differences by event type, player position, and location of impact. Game impact magnitudes were significantly greater than practice impacts. Impacts sustained by forwards were similar in magnitude to those sustained by defensemen. Significant differences between head impact locations across all player positions were observed. Impacts to the top of the head were significantly greater than impacts to the back, front, left, and right sides. Youth ice hockey players sustain helmet impacts nearing 20 g on average, similar to measured values in collegiate American football players, and of potential concern because this sample involves younger athletes. Future biomechanical studies are needed to better interpret the finding that there is an increased likelihood of higher magnitude head impacts to the top of the head. The authors' long-term goal is to improve the understanding of impacts that may lead to concussions in young athletes.