James T. Eckner

Cumulative head impact burden in high school football

Impacts to the head are common in collision sports such as football. Emerging research has begun to elucidate concussion tolerance levels, but sub-concussive impacts that do not result in clinical signs or symptoms of concussion are much more common, and are speculated to lead to alterations in cerebral structure and function later in life. We investigated the cumulative number of head impacts and their associated acceleration burden in 95 high school football players across four seasons of play using the Head Impact Telemetry System (HITS). The 4-year investigation resulted in 101,994 impacts collected across 190 practice sessions and 50 games. The number of impacts per 14-week season varied by playing position and starting status, with the average player sustaining 652 impacts. Linemen sustained the highest number of impacts per season (868); followed by tight ends, running backs, and linebackers (619); then quarterbacks (467); and receivers, cornerbacks, and safeties (372). Post-impact accelerations of the head also varied by playing position and starting status, with a seasonal linear acceleration burden of 16,746.1g, while the rotational acceleration and HIT severity profile burdens were 1,090,697.7 rad/sec(2) and 10,021, respectively. The adolescent athletes in this study clearly sustained a large number of impacts to the head, with an impressive associated acceleration burden as a direct result of football participation. These findings raise concern about the relationship between sub-concussive head impacts incurred during football participation and late-life cerebral pathogenesis, and justify consideration of ways to best minimize impacts and mitigate cognitive declines.

Pilot Evaluation of a Novel Clinical Test of Reaction Time in National Collegiate Athletic Association Division I Football Players

CONTEXT Evidence suggests that concussion prolongs reaction time (RT). We have developed a simple, reliable clinical tool for measuring reaction time that may be of value in the assessment of concussion in athletes. OBJECTIVE To compare baseline values of clinical RT (RT(clin)) obtained using the new clinical reaction time apparatus with computerized RT (RT(comp)) obtained using a validated computerized neuropsychological test battery. DESIGN Cross-sectional study. SETTING Data were collected during a National Collegiate Athletic Association Division I collegiate football teams preparticipation physical examination session. PATIENTS OR OTHER PARTICIPANTS Ninety-four Division I collegiate football players. MAIN OUTCOME MEASURE(S) The RT(clin) was measured using a 1.3-m measuring stick embedded in a weighted rubber disk that was released and caught as quickly as possible. The RT(comp) was measured using the simple RT component of CogState Sport. RESULTS For the 68 athletes whose CogState Sport tests passed the programs integrity check, RT(clin) and RT(comp) were correlated (r = 0.445, P < .001). Overall, mean RT(clin) was shorter and less variable than mean RT(comp) (203 +/- 20 milliseconds versus 268 +/- 44 milliseconds; P < .001). When RT(clin) and RT(comp) were compared between those athletes with (n = 68) and those without (n = 26) valid CogState Sport test sessions, mean RT(clin) was similar (202 +/- 19 milliseconds versus 207 +/- 23 milliseconds; P = .390), but mean RT(comp) was different (258 +/- 35 milliseconds versus 290 +/- 55 milliseconds; P = .009). CONCLUSIONS The RT(clin) was positively correlated with RT(comp) and yielded more consistent reaction time values during baseline testing. Given that RT(clin) is easy to measure using simple, inexpensive equipment, further prospective study is warranted to determine its clinical utility in the assessment of concussion in athletes.

Post-concussion cognitive declines and symptomatology are not related to concussion biomechanics in high school football players

Concussion is a major public health concern with nearly 4 million injuries occurring each year in the United States. In the acute post-injury stage, concussed individuals demonstrate cognitive function and motor control declines as well as reporting increased symptoms. Researchers have hypothesized that the severity of these impairments is related to impact magnitude. Using the Head Impact Telemetry System (HITS) to record head impact biomechanics, we sought to correlate pre- and post-concussive impact characteristics with declines in cognitive performance and increases in concussion-related symptoms. Over four seasons, 19 high school football athletes wearing instrumented helmets sustained 20 diagnosed concussions. Each athlete completed a baseline computer-based symptom and cognitive assessment during the pre-season and a post-injury assessment within 24 h of injury. Correlational analyses identified no significant relationships between symptoms and cognitive performance change scores and impact biomechanics (i.e., time from session start until injury, time from the previous impact, peak linear acceleration, peak rotational acceleration, and HIT severity profile [HITsp]). Nor were there any significant relationships between change scores and the number of impacts, cumulative linear acceleration, cumulative rotational acceleration, or cumulative HITsp values associated with all impacts prior to or following the injury. This investigation is the first to examine the relationship between concussion impact characteristics, including cumulative impact profiles, and post-morbid outcomes in high school athletes. There appears to be no association between head impact biomechanics and post-concussive outcomes. As such, the use of biomechanical variables to predict injury severity does not appear feasible at this time.

Cognitive decline and aging: The role of concussive and subconcussive impacts

Concussion has been viewed historically as a transient injury with no evidence supporting the existence of persistent effects. However, our recent work demonstrates electroencephalographic and motor control changes in otherwise healthy individuals with a history of concussion. We therefore hypothesize that concussive and subconcussive head impacts set about a cascade of pathological events that accelerates declines in cognitive function typically associated with the aging process.

At-risk populations in sports-related concussion.

Concussion is a physiological injury to the extremely complex and dynamic human brain. Individual variability adds to the challenge of concussion management, and sports medicine practitioners recently have begun to realize the need for an individualized approach. Adequately assessing an athlete with concussion requires consideration of many risk factors, including age, gender, and certain comorbid conditions. Understanding how these factors may affect concussion risk and outcome is becoming an essential aspect of management. This article reviews what is known or assumed about how some of these risk factors affect concussion. We conclude by providing several key concepts that we feel are important to keep in mind when managing an athlete with concussion.

Between-Seasons Test-Retest Reliability of Clinically Measured Reaction Time in National Collegiate Athletic Association Division I Athletes

CONTEXT Reaction time is typically impaired after concussion. A clinical test of reaction time (RT(clin)) that does not require a computer to administer may be a valuable tool to assist in concussion diagnosis and management. OBJECTIVE To determine the test-retest reliability of RTclinmeasured over successive seasons in competitive collegiate athletes and to compare these results with a computerized measure of reaction time (RT(comp)). DESIGN Case series with repeated measures. SETTING Preparticipation physical examinations for the football, womens soccer, and wrestling teams at a single university. PATIENTS OR OTHER PARTICIPANTS 102 National Collegiate Athletic Association Division I athletes. INTERVENTION(S) The RT(clin) was measured using a measuring stick embedded in a weighted rubber disk that was released and caught as quickly as possible. The RT(comp) was measured using the simple reaction time component of CogState Sport. MAIN OUTCOME MEASURE(S) Data were collected at 2 time points, 1 season apart, during preparticipation physical examinations. Outcomes were mean simple RT(clin) and RT(comp). RESULTS The intraclass correlation coefficient estimates from season 1 to season 2 were 0.645 for RT(clin) (n = 102, entire sample) and 0.512 for RT(comp) (n = 62 athletes who had 2 consecutive valid baseline CogState Sport test sessions). CONCLUSIONS The test-retest reliability of RT(clin) over consecutive seasons compared favorably with that of a concurrently tested computerized measure of reaction time and with literature-based estimates of computerized reaction time measures. This finding supports the potential use of RT(clin) as part of a multifaceted concussion assessment battery. Further prospective study is warranted.

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.

Effect of Neck Muscle Strength and Anticipatory Cervical Muscle Activation on the Kinematic Response of the Head to Impulsive Loads

Background: Greater neck strength and activating the neck muscles to brace for impact are both thought to reduce an athlete’s risk of concussion during a collision by attenuating the head’s kinematic response after impact. However, the literature reporting the neck’s role in controlling postimpact head kinematics is mixed. Furthermore, these relationships have not been examined in the coronal or transverse planes or in pediatric athletes. Hypotheses: In each anatomic plane, peak linear velocity (ΔV) and peak angular velocity (Δω) of the head are inversely related to maximal isometric cervical muscle strength in the opposing direction (H1). Under impulsive loading, ΔV and Δω will be decreased during anticipatory cervical muscle activation compared with the baseline state (H2). Study Design: Descriptive laboratory study. Methods: Maximum isometric neck strength was measured in each anatomic plane in 46 male and female contact sport athletes aged 8 to 30 years. A loading apparatus applied impulsive test forces to athletes’ heads in flexion, extension, lateral flexion, and axial rotation during baseline and anticipatory cervical muscle activation conditions. Multivariate linear mixed models were used to determine the effects of neck strength and cervical muscle activation on head ΔV and Δω. Results: Greater isometric neck strength and anticipatory activation were independently associated with decreased head ΔV and Δω after impulsive loading across all planes of motion (all P < .001). Inverse relationships between neck strength and head ΔV and Δω presented moderately strong effect sizes (r = 0.417 to r = 0.657), varying by direction of motion and cervical muscle activation. Conclusion: In male and female athletes across the age spectrum, greater neck strength and anticipatory cervical muscle activation (“bracing for impact”) can reduce the magnitude of the head’s kinematic response. Future studies should determine whether neck strength contributes to the observed sex and age group differences in concussion incidence. Clinical Relevance: Neck strength and impact anticipation are 2 potentially modifiable risk factors for concussion. Interventions aimed at increasing athletes’ neck strength and reducing unanticipated impacts may decrease the risk of concussion associated with sport participation.

Effect of sport-related concussion on clinically measured simple reaction time

Background Reaction time (RT) is a valuable component of the sport concussion assessment battery. RT is typically measured using computers running specialised software, which limits its applicability in some athletic settings and populations. To address this, we developed a simple clinical test of RT (RTclin) that involves grasping a falling measuring stick. Purpose To determine the effect of concussion on RTclin and its sensitivity and specificity for concussion. Materials and methods Concussed athletes (n=28) and non-concussed control team-mates (n=28) completed RTclin assessments at baseline and within 48 h of injury. Repeated measures analysis of variance compared mean baseline and follow-up RTclin values between groups. Sensitivity and specificity were calculated over a range of reliable change confidence levels. Results RTclin differed significantly between groups (p<0.001): there was significant prolongation from baseline to postinjury in the concussed group (p=0.003), with a trend towards improvement in the control group (p=0.058). Sensitivity and specificity were maximised when a critical change value of 0 ms was applied (ie, any increase in RTclin from baseline was interpreted as abnormal), which corresponded to a sensitivity of 75%, specificity of 68% and a 65% reliable change confidence level. Conclusions RTclin appears sensitive to the effects of concussion and distinguished concussed and non-concussed athletes with similar sensitivity and specificity to other commonly used concussion assessment tools. Given its simplicity, low cost and minimal time requirement, RTclin should be considered a viable component of the sports medicine providers multifaceted concussion assessment battery.

Subconcussive head impact biomechanics: comparing differing offensive schemes.

PURPOSE 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. METHODS 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. RESULTS 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. CONCLUSIONS 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.