Jason P. Mihalik

Concussion in Sports: Postconcussive Activity Levels, Symptoms, and Neurocognitive Performance

CONTEXT Evidence suggests that athletes engaging in high-intensity activities after concussion have more difficulties with cognitive recovery. OBJECTIVE To examine the role postinjury activity level plays in postconcussive symptoms and performance on neurocognitive tests in a population of student-athletes. DESIGN Retrospective cohort study with repeated measures of neurocognitive performance and symptom reporting. SETTING University-based sports concussion clinic. PATIENTS OR OTHER PARTICIPANTS Ninety-five student-athletes (80 males, 15 females: age = 15.88 +/- 1.35 years) were retrospectively assigned to 1 of 5 groups based on a postinjury activity intensity scale. MAIN OUTCOME MEASURE(S) We employed a regression analysis for repeated measures to evaluate the relationship of activity intensity to symptoms and neurocognitive outcome up to 33 days after concussion. Postconcussion symptom scores and neurocognitive (verbal memory, visual memory, visual motor speed, and reaction time) scores served as the primary outcome measures. RESULTS Level of exertion was significantly related to all outcome variables (P < .02 for all comparisons). With multivariate analysis, activity intensity remained significant with respect to visual memory (P = .003) and reaction time (P < .001). CONCLUSIONS Activity level after concussion affected symptoms and neurocognitive recovery. Athletes engaging in high levels of activity after concussion demonstrated worse neurocognitive performance. For these tasks, those engaging in moderate levels of activity demonstrated the best performance.

Measurement of head impacts in collegiate football players: An investigation of positional and event-type differences

OBJECTIVEThere exists a need to better understand the biomechanical forces associated with head impacts in American football. The purpose of this study was to investigate whether or not differences in head accelerations existed between different player positions and different event types in collegiate football. We also sought to identify whether or not any associations existed between high-magnitude impacts and location of head impacts. METHODSWe conducted a prospective field study in which accelerometers were embedded in the football helmets of 72 collegiate football players. Linear accelerations of all head impacts sustained over the course of the 2005 and 2006 National Collegiate Athletic Association football seasons were collected. One-way analyses of variance and χ2 tests of association assessed positional, event type, and location of head impact differences. RESULTSFootball players consistently sustained head impacts between 21 and 23 g. Positional differences were identified within our sample. Impacts sustained during helmets-only practices were greater than those sustained in games or scrimmages. There was an association between position and high-magnitude impacts, as well as between high-magnitude impacts and location of head impact, with the likelihood of impacts to the top of the head much higher than those to the front, back, left, and right sides. CONCLUSIONLess than 0.35% of impacts exceeding theoretical injury thresholds resulted in concussion. More injury data are required before any theoretical thresholds for injury can be confirmed. Coaches and sports medicine professionals should recognize that head impacts sustained in helmets-only practices are as severe as games or scrimmages; there seem to be no “light” days for football players.

Biomechanics of Sport Concussion: Quest for the Elusive Injury Threshold

Previous concussion biomechanics research has relied heavily on the animal model or laboratory reconstruction of concussive injuries captured on video footage. Real-time data collection involves a novel approach to better understanding the medical issues related to sport concussion. Recent studies suggest that a concussive injury threshold is elusive and may, in fact, be irrelevant when predicting the clinical outcome.

Return of Postural Control to Baseline After Anaerobic and Aerobic Exercise Protocols

CONTEXT With regard to sideline concussion testing, the effect of fatigue associated with different types of exercise on postural control is unknown. OBJECTIVE To evaluate the effects of fatigue on postural control in healthy college-aged athletes performing anaerobic and aerobic exercise protocols and to establish an immediate recovery time course from each exercise protocol for postural control measures to return to baseline status. DESIGN Counterbalanced, repeated measures. SETTING Research laboratory. PATIENTS OR OTHER PARTICIPANTS Thirty-six collegiate athletes (18 males, 18 females; age = 19.00 +/- 1.01 years, height = 172.44 +/- 10.47 cm, mass = 69.72 +/- 12.84 kg). INTERVENTION(S) Participants completed 2 counterbalanced sessions within 7 days. Each session consisted of 1 exercise protocol followed by postexercise measures of postural control taken at 3-, 8-, 13-, and 18-minute time intervals. Baseline measures were established during the first session, before the specified exertion protocol was performed. MAIN OUTCOME MEASURE(S) Balance Error Scoring System (BESS) results, sway velocity, and elliptical sway area. RESULTS We found a decrease in postural control after each exercise protocol for all dependent measures. An interaction was noted between exercise protocol and time for total BESS score (P = .002). For both exercise protocols, all measures of postural control returned to baseline within 13 minutes. CONCLUSIONS Postural control was negatively affected after anaerobic and aerobic exercise protocols as measured by total BESS score, elliptical sway area, and sway velocity. The effect of exertion lasted up to 13 minutes after each exercise was completed. Certified athletic trainers and clinicians should be aware of these effects and their recovery time course when determining an appropriate time to administer sideline assessments of postural control after a suspected mild traumatic brain injury.

Collision Type and Player Anticipation Affect Head Impact Severity Among Youth Ice Hockey Players

OBJECTIVE: The objective was to determine how body collision type and player anticipation affected the severity of head impacts sustained by young athletes. For anticipated collisions, we sought to evaluate different body position descriptors during delivery and receipt of body collisions and their effects on head impact severity. We hypothesized that head impact biomechanical features would be more severe in unanticipated collisions and open-ice collisions, compared with anticipated collisions and collisions along the playing boards, respectively. METHODS: Sixteen ice hockey players (age: 14.0 ± 0.5 years) wore instrumented helmets from which biomechanical measures (ie, linear acceleration, rotational acceleration, and severity profile) associated with head impacts were computed. Body collisions observed in video footage captured over a 54-game season were evaluated for collision type (open ice versus along the playing boards), level of anticipation (anticipated versus unanticipated), and relative body positioning by using a new tool developed for this purpose. RESULTS: Open-ice collisions resulted in greater head linear (P = .036) and rotational (P = .003) accelerations, compared with collisions along the playing boards. Anticipated collisions tended to result in less-severe head impacts than unanticipated collisions, especially for medium-intensity impacts (50th to 75th percentiles of severity scores). CONCLUSION: Our data underscore the need to provide players with the necessary technical skills to heighten their awareness of imminent collisions and to mitigate the severity of head impacts in this sport.

The relationship between subconcussive impacts and concussion history on clinical measures of neurologic function in collegiate football players.

Concussions sustained during college and professional football careers have been associated with both acute and chronic neurologic impairment. The contribution of subconcussive impacts to this impairment has not been adequately studied. Therefore, we investigated the relationship between subconcussive impacts and concussion history on clinical measures of neurologic function. Forty-six collegiate football players completed five clinical measures of neurologic function commonly employed in the evaluation of concussion before and after a single season. These tests included the Automated Neuropsychological Assessment Metrics, Sensory Organization Test, Standardized Assessment of Concussion, Balance Error Scoring System, and Graded Symptom Checklist. The Head Impact Telemetry (HIT) System recorded head impact data including the frequency, magnitude, and location of impacts. College football players sustain approximately 1,000 subconcussive impacts to the head over the course of a season, but for the most part, do not demonstrate any clinically meaningful changes from preseason to postseason on measures of neurologic function. Changes in performance were mostly independent of prior concussion history, and the total number, magnitude and location of sustained impacts over one season as observed R2 values ranged between 0.30 and 0.35. Repetitive subconcussive head impacts over a single season do not appear to result in short-term neurologic impairment, but these relationships should be further investigated for a potential dose–response over a player’s career.

Head impact exposure sustained by football players on days of diagnosed concussion

PURPOSE This study compares the frequency and severity of head impacts sustained by football players on days with and without diagnosed concussion and to identify the sensitivity and specificity of single-impact severity measures to diagnosed injury. METHODS One thousand two hundred eight players from eight collegiate football teams and six high school football teams wore instrumented helmets to measure head impacts during all team sessions, of which 95 players were diagnosed with concussion. Eight players sustained two injuries and one sustained three, providing 105 injury cases. Measures of head kinematics (peak linear and rotational acceleration, Gadd severity index, head injury criteria (HIC15), and change in head velocity (Δv)) and the number of head impacts sustained by individual players were compared between days with and without diagnosed concussion. Receiver operating characteristic curves were generated to evaluate the sensitivity and specificity of each kinematic measure to diagnosed concussion using only those impacts that directly preceded diagnosis. RESULTS Players sustained a higher frequency of impacts and impacts with more severe kinematic properties on days of diagnosed concussion than on days without diagnosed concussion. Forty-five injury cases were immediately diagnosed after head impact. For these cases, peak linear acceleration and HIC15 were most sensitive to immediately diagnosed concussion (area under the curve = 0.983). Peak rotational acceleration was less sensitive to diagnosed injury than all other kinematic measures (P = 0.01), which are derived from linear acceleration (peak linear, HIC15, Gadd severity index, and Δv). CONCLUSIONS Players sustained more impacts and impacts of higher severity on days of diagnosed concussion than on days without diagnosed concussion. In addition, of historical measures of impact severity, those associated with peak linear acceleration are the best predictors of immediately diagnosed concussion.

The National Football League Combine: Performance Differences Between Drafted and Nondrafted Players Entering the 2004 and 2005 Drafts

The purpose of this study was to examine performance differences between drafted and nondrafted athletes (N = 321) during the 2004 and 2005 National Football League (NFL) Combines. We categorized players into one of 3 groups: Skill, Big skill, and Linemen. Skill players (SP) consisted of wide receivers, cornerbacks, free safeties, strong safeties, and running backs. Big skill players (BSP) included fullbacks, linebackers, tight ends, and defensive ends. Linemen (LM) consisted of centers, offensive guards, offensive tackles, and defensive tackles. We analyzed player height and mass, as well as performance on the following combine drills: 40-yard dash, 225-lb bench press test, vertical jump, broad jump, pro-agility shuttle, and the 3-cone drill. Student t-tests compared performance on each of these measures between drafted and nondrafted players. Statistical significance was found between drafted and nondrafted SP for the 40-yard dash (P < 0.001), vertical jump (P = 0.003), pro-agility shuttle (P < 0.001), and 3-cone drill (P < 0.001). Drafted and nondrafted BSP performed differently on the 40-yard dash (P = 0.002) and 3-cone drill (P = 0.005). Finally, drafted LM performed significantly better than nondrafted LM on the 40-yard dash (P = 0.016), 225-lb bench press (P = 0.003), and 3-cone drill (P = 0.005). Certified strength and conditioning specialists will be able to utilize the significant findings to help better prepare athletes as they ready themselves for the NFL Combine.

The effects of an exercise intervention on forward head and rounded shoulder postures in elite swimmers

Objectives To examine the correction of posture, increase in strength and decrease in shoulder pain and dysfunction in varsity swimmers. Design and Setting Randomised clinical trial. Participants Twenty-eight National Collegiate Athletic Association division I varsity swimmers. Measurements Two testing sessions were conducted before and after an 8-week time period. Posture, strength and shoulder pain and function were assessed. Forward head angle was measured using a digital inclinometer, forward head translation was measured using a ruler and total scapular distance was measured with unmarked string. Average and peak values (N) of strength were measured with the hand-held dynamometer. The intervention subjects then participated in an 8-week exercise training programme to correct posture. The procedures were then repeated in the post-test. Results Significant group by time interactions (p<0.05) were found in forward head angle and forward shoulder translation indicating a decrease in forward head angle and forward shoulder translation. Significant main effects for time (p<0.05) were found in strength measures for all muscle groups indicating increased strength for shoulder girdle muscles tested. Conclusions The exercise intervention was successful at decreasing forward head and rounded shoulder postures in elite swimmers. This study supports the theoretical basis for clinical rehabilitation of posture and the shoulder.

MEASUREMENT OF HEAD IMPACTS IN COLLEGIATE FOOTBALL PLAYERS: CLINICAL MEASURES OF CONCUSSION AFTER HIGH- AND LOW-MAGNITUDE IMPACTS

OBJECTIVEIt has been speculated that a theoretical injury threshold of 70 to 75 g may exist for concussions in football players. We aimed to investigate acute balance and neurocognitive performance after head impacts exceeding a theoretical injury threshold in the absence of both self-reported symptoms and a concussion diagnosis 24 hours before testing. METHODSForty-three Division I collegiate football players participated in this double-blind, repeated-measures study. Subjects participated in three test sessions (baseline, low impact, and high impact) separated by at least 2 weeks. The Head Impact Telemetry System (Simbex, Lebanon, NH) recorded real-time head impacts sustained during practices and games. The Automated Neuropsychological Assessment Metrics assessed neurocognitive performance. The NeuroCom Sensory Organization Test (NeuroCom International Inc., Clackamas, OR) assessed postural stability. The Graded Symptom Checklist evaluated symptom presence and severity in our participants. RESULTSAfter the low-impact test session (<60 g), we observed improvements in the Math Processing (F1, 26 = 9.797; P = 0.004), Matching to Sample (F1, 26 = 6.504; P = 0.017), and Sternberg Procedure (F1, 26 = 5.323; P = 0.030) Automated Neuropsychological Assessment Metrics test modules. Statistically significant differences were also observed after the high-impact test session (>90g) with improvements in Math Processing (F1, 22 = 16.629; P < 0.001), Procedural Reaction Time (F1, 22 = 14.668; P < 0.001), and the total number of symptoms reported (F1, 22 = 10.267; P = 0.004). Neurocognitive improvements were likely attributed to a learning effect. CONCLUSIONOur findings suggest that sustaining an impact greater than 90 g does not result in acute observable balance and neurocognitive deficits within 24 hours of sustaining the impact. Although previous studies have suggested a theoretical injury threshold, none have been founded on empirical data collected on the playing field in real-time. Future studies should consider the cumulative effects of impacts of varying magnitudes.