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Symptom resolution is a key marker in determining fitness for return to activity following concussion, but in some cases, distinguishing persistent symptoms due to concussion versus symptoms related to other factors can be challenging. To determine base rates of postconcussional syndrome (PCS) diagnostic categorization in healthy cadets and student athletes with no recent concussion. 13,009 cadets and 21,006 student athletes completed baseline preseason testing. After inclusion/exclusion criteria were applied, the final sample included 12,039 cadets [9123 men (75.8%); 2916 women (24.2%)] and 18,548 student athletes [10,192 men (54.9%); 8356 women (45.1%)]. Participants completed the Sport Concussion Assessment Tool–3rd Edition (SCAT3) symptom evaluation as part of baseline preseason testing. The PCS diagnostic categorization was classified by the International Classification of Diseases, 10th Revision (ICD-10) symptom criteria for PCS. In the absence of recent concussion, subgroups of cadets (17.8% of men; 27.6% of women) and student athletes (11.4% of men; 20.0% of women) reported a cluster of symptoms that would meet the ICD-10 symptom criteria for PCS. Participants with insufficient sleep and/or preexisting conditions (e.g., mental health problems), freshmen cadets, and cadets at the U.S. Coast Guard Academy and at the U.S. Air Force Academy (freshmen were tested during basic cadet training) were more likely to report a cluster of symptoms that would meet the ICD-10 symptom criteria for PCS. The ICD-10 symptom criteria for PCS can be mimicked by preexisting conditions, insufficient sleep, and/or stress. Findings support person-specific assessment and management of symptoms following concussion.

ObjectiveTo examine the association between estimated age at first exposure (eAFE) to American football and clinical measures throughout recovery following concussion.MethodsParticipants were recruited across 30 colleges and universities as part of the National Collegiate Athletic Association (NCAA)–Department of Defense Concussion Assessment, Research and Education Consortium. There were 294 NCAA American football players (age 19 ± 1 years) evaluated 24–48 hours following concussion with valid baseline data and 327 (age 19 ± 1 years) evaluated at the time they were asymptomatic with valid baseline data. Participants sustained a medically diagnosed concussion between baseline testing and postconcussion assessments. Outcome measures included the number of days until asymptomatic, Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) composite scores, Balance Error Scoring System (BESS) total score, and Brief Symptom Inventory 18 (BSI-18) subscores. The eAFE was defined as participant's age at the time of assessment minus self-reported number of years playing football.ResultsIn unadjusted regression models, younger eAFE was associated with lower (worse) ImPACT Visual Motor Speed (R2 = 0.031, p = 0.012) at 24–48 hours following injury and lower (better) BSI-18 Somatization subscores (R2 = 0.014, p = 0.038) when the athletes were asymptomatic. The effect sizes were very small. The eAFE was not associated with the number of days until asymptomatic, other ImPACT composite scores, BESS total score, or other BSI-18 subscores.ConclusionEarlier eAFE to American football was not associated with longer symptom recovery, worse balance, worse cognitive performance, or greater psychological distress following concussion. In these NCAA football players, longer duration of exposure to football during childhood and adolescence appears to be unrelated to clinical recovery following concussion.

OBJECTIVES: To test whether 1) concussed athletes demonstrate slower tandem gait times compared to controls and 2) concussed female athletes display greater post-injury deficits than males. DESIGN: Prospective longitudinal METHOD: Fifty concussed collegiate student-athletes (32% female, age= 20.18±1.27 years) completed tandem gait tests during pre-season (Time 1) and acutely (

Context Postconcussion deficits in neurocognitive performance and postural control may persist at the time of return to sport participation. How these deficits, if present, affect athletic performance is largely unknown, with prior studies showing mixed results. Objective To evaluate postconcussion National Hockey League player performance using advanced hockey metrics over short- (5 games), medium- (10 games), and long-term (remainder of the season) seasonal performance. Design Retrospective cohort study. Patients or Other Participants National Hockey League players who sustained a sport-related concussion (SRC; n = 93) and returned during the same season and players (n = 51) who missed time for non–injury-related reasons. Main Outcome Measure(s) Six performance metrics were used: (1) points per 60 minutes, (2) Corsi percentage, (3) personal Fenwick shooting percentage, (4) scoring chances per 60 minutes, (5) penalty difference, and (6) PDO (not an acronym but sometimes referred to as SVSP% [save percentage shooting percentage]). Performance was compared using 2 (group) × 2 (time) repeated-measures analyses of variance for 3 time windows: (1) ±5 games, (2) ±10 games, and (3) the remainder of the season postconcussion. Alpha values were set at a conservative .01 to account for the lack of independence among dependent variables. Results No significant interactions were present for any of the 6 dependent variables at any of the 3 time windows. Overall, none of the secondary variables differed. Conclusions Using advanced, sport-specific metrics, we found that National Hockey League players did not display worse seasonal performance during 3 postinjury time frames after they sustained an SRC. Whereas laboratory studies have identified lingering neurologic deficits after concussion, our results suggest that these deficits, if present, either do not translate to worse athletic performance or were not captured by these 44 metrics. Further, prospective efforts are needed to accurately quantify performance after SRC among professional hockey players.

ObjectiveTo examine neurocognitive performance of persistent concussion symptom patients using a novel sensorimotor technology.BackgroundIn patients with persistent concussion symptoms, neurocognitive deficits have been routinely identified; however, most of the current literature focuses on athletes and military veterans. Middle aged community members face unique challenges related to jobs, family, and transportation which can all be adversely affected by neurocognitive deficits.Design/MethodsThirteen adults (44.3 ± 12.6 years) with self-reported persistent-concussion symptoms (PCS) at least 3 months post-injury, and thirteen sex and age matched healthy controls (37.5 ± 8.8 years) were recruited. Participants performed the Trail-Making Test A (TMT-A) and Trail-Making Test B (TMT-B) on a novel sensorimotor assessment tool, the KINARM (BKIN Technologies, Kingston, ON, Canada). Using their dominant hand, TMT-A required participants to connect numbered dots in ascending order as quickly as possible. TMT-B required connecting dots with either a number or letter inside, in an alternating number-letter fashion (i.e.,: 1-A-2-B-3-C…). Total number of symptoms and a symptom severity score were assessed using the Rivermead Post Concussion Symptoms Questionnaire (RPQ). An independent samples t-test was used to analyze group differences of total time to completion, dwell time, and number of errors.ResultsAs expected, PCS patients had a significantly higher number of symptoms and severity score (PCS: 13.4 ± 2.3 and 36.2 ± 14.5, respectively; Controls: 3.4 ± 3.7 and 5.3 ± 5.6, respectively, p < 0.001). PCS patients were significantly slower on TMT-A (46.3 ± 20.1 sec; and 34.7 ± 6.5 sec respectively, p = 0.047). There were no group differences in TMT-B.ConclusionsOur results suggest that neurocognitive function may remain unaffected by persistent concussion symptoms in working-aged adults. The lack of task performance differences may be a result of neurocognitive function recovery, or the need for a more sensitive task to assess neurocognitive function in this population.

ObjectiveTo determine the effect of concussion history on the electronic version of the Trail Making Test (TMT) A and TMT-B performance.BackgroundThe effects of concussion history on cognitive performance when the individual is still young has received limited attention. There are inconsistent results in prior studies using computerized neurocognitive tests however the TMT assesses divergent neurologic systems including working memory, horizontal and vertical saccades, attention, cognitive processing, and executive function. While the TMT has routinely identified deficits acutely post-concussion, the long-term effect of prior concussions has not been established.Design/MethodsThis study utilized a cross-sectional design of 50 current intercollegiate division I athletes (56% female, age: 19.8 ± 1.3 y.o.). Participants completed a reliable concussion history questionnaire as well as the TMT-A and TMT-B on an iPad at baseline. The independent variable was concussion history and the dependent variables were total time on TMT-A and TMT-B which were compared by independent samples t-tests or Mann-Whitney U test.ResultsOf the 50 student athletes 26 (52%) reported at least one previously diagnosed concussion. There was no significant difference between groups for the TMT-A (No prior concussion: 22.9 + 6.1 sec and Concussion history: 19.7 + 4.1, U = 227.0, p = 0.10) or TMT-B (No prior concussion: 42.1 + 13.2 sec and concussion history: 38.1 + 11.3, t = 1.17, p = 0.25).ConclusionsThe results of this study suggest that while still in college, a history of one or more prior concussions, did not adversely affect neurocognitive performance on either the TMT-A or B test. As concussion history is sometimes associated with later life neurocognitive performance, future studies should assess TMT-A and B across the lifespan.

ObjectiveTo assess the association between the Brief Symptom Inventory 18 (BSI-18) response at post-concussion return to play (RTP) and subsequent lower extremity musculoskeletal injury (LE-MSI).BackgroundConcussion evaluation includes a multifaceted neurologic assessment at baseline and post-injury. Despite emotional sequelae after concussion, psychological assessments have received limited attention thus athletes may RTP despite persistent psychological distress post-concussion. Recent evidence has suggested an ∼2x elevated rate of post-concussion LE-MSI in collegiate athletes; however there is limited understanding of potential mechanisms. As psychological distress has been associated with MSI, the purpose of this study was to assess BSI-18 as a potential predictor of subsequent MSI.Design/MethodsThis analysis utilized a cross-sectional design of 67 NCAA intercollegiate students-athletes with a diagnosed concussion (59.7% female, age: 19.7 ± 1.4 years). Participants completed the BSI-18, an 18-item questionnaire based on a 5-point Likert scale (0–4) used to measure psychological distress at the RTP clinical time-point. Outcome measures were the Global Severity Index (GSI) which is the total score of symptoms (0–72) with higher scores representing greater psychological distress and subsequent MSI (yes or no) collected retrospectively through an electronic medical record in the year following diagnosed concussion. Binary logistic regression was used to assess the predictive capabilities of BSI-18 GSI and subsequent LE-MSI.ResultsThe BSI-18 GSI did not significantly predict subsequent LE-MSI (p = 0.095, Exp(B) = 2.436, Nagelkerke R2 = 0.181).ConclusionsThe BSI-18 GSI at RTP did not predict post-concussion subsequent LE-MSI. While the underlying mechanism for post-concussion MSI remains to be fully elucidated, results suggest that psychological health, as measured by the BSI-18 GSI, at RTP is not associated with subsequent LE-MSI. If MSI risk can be predicted then targeted, established, and clinically feasible injury prevention programs can be implemented to reduce injury risk.

ObjectivesTo determine the effect of heading a soccer ball on serum neurofilament light (NF-L) protein, plasma tau protein and symptom metrics including total number of symptoms reported and symptom severity scores on the Standardized Concussion Assessment Tool— 3rd edition (SCAT3).MethodsEleven male collegiate soccer players were recruited to take part in three experimental conditions including heading, sham and control conditions. Participants were required to perform 40 headers in 20 min in the heading condition, and control 40 soccer balls directed at them with their hands, chest or thigh in the sham condition. No ball contact was made during the control condition. Blood sampling and SCAT3 symptom assessments were completed prior to and 1 hour following conditions. A subset of participants returned 3 weeks following the heading condition for blood sampling.ResultsNF-L was elevated at 1 hour (p=0.004) and 1 month (p=0.04) following the heading condition, and at 1 hour (p=0.02) following the control condition. Tau levels remained unchanged following all conditions. The total number of symptoms (TS) and symptom severity (SS) scores from the SCAT3 were both elevated following the heading condition (p=0.01 and p=0.03, respectively). Both TS and SS decreased following sham (p=0.04 and p=0.04) and control conditions (p=0.04 and p=0.04).ConclusionAn acute bout of soccer heading is associated with increased NF-L concentrations at 1 hour and 1 month following the session and can lead to symptoms commonly reported following sport-related concussion.

Sport-related concussion is known to affect a variety of brain functions. However, the impact of this brain injury on cerebral autoregulation is poorly understood. Thus, the goal of the current study was to determine the acute and cumulative effects of sport-related concussion on indices of dynamic cerebral autoregulation. Towards this end, 179 elite, junior-level (age 19.6 ± 1.5 years) contact sport (ice hockey, American football) athletes recruited for pre-season testing, 42 with zero prior concussions and 31 with three or more previous concussions. Eighteen athletes sustained a concussion during that competitive season, and completed follow-up testing at 72-hours, 2-weeks, and 1-month post-injury. Beat-by-beat arterial blood pressure (BP) and middle cerebral artery blood velocity (MCAv) were recorded using finger photoplethysmography and transcranial Doppler ultrasound, respectively. Five minutes of repetitive squat-stand manoeuvres induced BP oscillations at 0.05 Hz and 0.10 Hz (20-s and 10-s cycles, respectively). The BP-MCAv relationship was quantified using transfer function analysis to estimate Coherence (correlation), Gain (amplitude ratio), and Phase (timing offset). At a group level, repeated-measures ANOVA indicated 0.10 Hz Phase was significantly reduced following an acute concussion, compared to preseason, by 23% (-0.136 ± 0.033 rads) at 72 hours and by 18% (-0.105 ± 0.029 rads) at 2-weeks post-injury, indicating impaired autoregulatory functioning; recovery to preseason values occurred by 1-month. Athletes were cleared to return to competition after a median of 14 days (range 7-35), implying physiologic dysfunction persisted beyond clinical recovery in many cases. When comparing dynamic pressure buffering between athletes with zero prior concussions and those with three or more, no differences were observed. Sustaining an acute sport-related concussion induces transient impairments in the capabilities of the cerebrovascular pressure-buffering system that may persist beyond two weeks, and may be due to a period of autonomic dysregulation. Athletes with a history of three or more concussions did not exhibit impairments relative to those with zero prior concussions, suggesting recovery of function over time. Findings from this study support the potential need to consider physiological recovery in deciding when patients should return-to-play following a concussion.

Objective: To determine whether acute sports-related concussion (SRC) exerts differential effects on cerebral autoregulatory properties during systole versus diastole.

Although balance control has been studied extensively following acute concussion, little is known regarding repetitive sub-concussive head impacts or chronic exposure to multiple concussive events. Quiet stance postural control was characterized in contact sport athletes at pre-season (n = 135) and post-season (n = 48) to evaluate the effects of subconcussive trauma to the head. To determine the impact of acute concussion on postural control, athletes diagnosed with a concussion during the season (n = 12) were tested at 72-h, 2-weeks, and 1-month post-injury. Because only 4 of the concussed athletes completed baseline testing, control athletes (n = 12) matched for sport, age, body mass index (BMI), and previous concussion history served as a comparison group. Finally, the effects of previous concussion history on quiet stance postural control were determined by comparing pre-season data in contact sport athletes with either zero (Hx0, n = 50) or three or more (Hx3+, n = 25) previous concussions. A force plate was used to compare changes in centre-of-pressure root-mean-square displacement (RMSdisp) and mean-velocity (COPvel) in the anterior/posterior (AP) and medial/lateral (ML) directions. One-minute trials were performed with feet hip-width apart, hands-on-hips, and A) eyes-open and B) eyes-closed. Biomechanical head-impact exposure (impacts over 10 g) was indexed over the season using mastoid-fixed impact sensors. In acutely injured athletes, repeated-measures ANOVA revealed a significant effect of time for RMSdisp AP with increased displacement at 2 weeks compared to 72 h (p = 0.008, 95% CI: −0.180, −0.310 cm). No other COP variables were affected by acute concussion. Moreover, there was no effect of concussion history or repeated sub-concussive impacts on any quiet stance metric. Additionally, head-impact exposure metrics were not correlated with COP metrics. Taken together, the data suggests alterations in COP sway during quiet stance persist in the acute 2-week period after injury. These findings were not present with either a history of multiple concussions or exposure to sub-concussive head impacts indicating acute concussion does not have appear to have long term effects for these measures.

ObjectiveTo examine sex differences in TG performance among collegiate student-athletes acutely post-concussion relative to pre-injury performance.BackgroundPostural control impairments are common following concussion and traditionally assessed using the Balance Error Scoring System (BESS). Tandem gait (TG) has successfully identified impairments in postural control acutely post-concussion that were undetected by the BESS; thus, TG may be a more robust postural control assessment following concussion. While sex differences in BESS performance after concussion have been explored, there is no literature regarding sex differences in post-concussion TG.Design/MethodsForty-eight concussed collegiate student-athletes (30 females) and twenty-five healthy controls (13 females) completed TG tests during pre-season and again acutely post-concussion. Participants walked heel-to-toe down a 3-meter line, turned, and returned as quickly as possible, completing four single-task (ST) and dual-task (DT) TG trials. During DT trials, they simultaneously answered mini-mental style questions. The best ST and DT times were recorded. A 2 × 2 (group*sex) ANOVA was used to examine TG change between pre-injury and post-injury tests (positive value = slower/worsening; negative value = faster/improving).ResultsThe change in TG time from pre-injury to post-injury was significantly higher for the concussion group relative to the control group during both ST (Concussion: 1.6 ± 2.6 seconds, Controls: −1.1 ± 0.8 seconds, p < 0.001) and DT (Concussion: 2.0 ± 3.8 seconds, Controls: −0.9 ± 1.7 seconds, p < 0.001) TG. There were no significant interactions (ST: p = 0.17, DT: p = 0.23) or main effects for sex (ST: p = 0.63, DT: p = 0.91).ConclusionsThere were no sex-specific differences in TG performance acutely post-concussion. However, all concussed participants, regardless of sex, performed significantly worse on TG than male and female controls after injury relative to baseline, while controls did not demonstrate such a change. These results suggest that TG can appropriately identify postural control impairments following concussion; however, there do not appear to be differences in performance between males and females.

ObjectiveTo examine the association between concussions and lower extremity musculoskeletal injury (LE-MSI) rates in Reserve Officer Training Corps (ROTC) cadets.BackgroundConcussions have been associated with an increased risk for LE-MSI among high school, collegiate, and professional athletes as well as U.S. Army Soldiers. However, there is a paucity evidence on this relationship among U.S. Army ROTC cadets, future U.S. Army Officers, and a group similar to student-athletes in regards to physical activity levels.Design/MethodsA modified reliable injury questionnaire (ICC = 0.92) was used to identify the total number of reported concussions, intentionally unreported concussions, and potentially unrecognized concussions (e.g., memory loss not diagnosed as a concussion) as well as LE-MSI (e.g., muscle strains, ACL rupture) a cadet had suffered. A chi-square analysis was performed to identify the association between concussion and LE-MSI and any concussive injury and LE-MSI.Results47 cadets (19.9 ± 1.3 years) were recruited from one Army ROTC program. There was not a significant association between reported concussions and LE-MSI (Χ(1) = 3.122, p = 0.077). There was not a significant association between any concussive injury (reported, unreported, or potentially unrecognized) and LE-MSI (Χ(1) = 3.590, p = 0.058). The reported concussion history was 38.3% (18/47), any concussive history was 46.8% (22/47), and 68.1% (32/47) reported history of LE-MSI.ConclusionsPreliminary results showed that there was no statistically significant association between concussion and LE-MSI among ROTC cadets at this university. Future research is warranted on a larger cohort of cadets to determine if this relationship exists since cadets will soon commission, potentially risking injury while serving on active duty, causing limited duty days, reduced Department of Defense readiness, and increased healthcare costs. Cadets showed a high incidence of concussion and LE-MSK injury, and future research should target reducing these injuries among ROTC cadets prior to commissioning.

Objective To examine how a season of sub-concussive head-impact exposures influence a measure of response-inhibition in contact-sport athletes. Design Prospective cohort Setting Laboratory Participants Twenty-five contact-sport athletes (20.3±1.3 years) performed a response-inhibition task prior to and following the competitive season. Each player wore an adhesive accelerometer (X2Biosystems) during games. Players were excluded if they sustained a concussion during the season. Interventions To probe response-inhibition, an object hit-and-avoid sensorimotor task (KINARM) was performed. This 2.5 minute task entailed the successful hitting of two target shapes while avoiding six other distractor shapes. Players were divided into tertiles (high, medium, low; n=8) based on cumulative number of 20g+ head impacts, cumulative peak linear acceleration (cPLA), and cumulative peak rotational acceleration (cPRA). Comparisons of response-inhibition performance were made between high and low tertiles. Outcome measures Pre-post changes in number of targets hit, distractors hit, total cancelled movements towards pursued distractors (CPDs), and total task accuracy (percent) were recorded for the KINARM task. Results Independent t-tests indicated no significant differences between the high and low tertiles on the KINARM task despite the high tertile group experiencing 4-times greater head impacts throughout the season. There was a trend for greater KINARM task improvement from pre-to-post-season in the bottom tertile, as reflected by the increase in CPDs in their post-season measures (cumulative number: p=0.06, CI=[−16.2148519, 0.7148519]). Conclusions These findings reveal that one season of repetitive sport-related head impacts does not appear to have a significant effect on an athlete’s ability to inhibit a motor response. Competing interests All authors have no competing interests to declare.

Objective To determine the influence of a history of 3+ previous concussions on quiet stance. Design Retrospective cohort. Setting Laboratory. Participants Eighty-seven male (age range 17–22) contact-sport athletes (football and hockey) entered the study. Participants were recruited from the same sport teams and tested during the pre-season. Exclusion criteria: concussion in the prior 6 months, or history of 1 or 2 concussions. Forty-four met the inclusion criteria: thirty-one had no previous concussions, and thirteen had a history of 3+ concussions. Interventions Participants held quiet upright stance on a force plate (NDI True Impulse) with feet hip-width apart and hands on hips with eyes-open (1 min), and closed (1 min). Independent variables included condition (2) and concussion history (2). Outcome measures Root-mean-square displacement (RMSd), and mean velocity of centre-of-pressure (COP) in the anterior/posterior (AP) and medial/lateral (ML) directions. Main results Mixed ANOVA indicated a significant condition effect in ML-RMSd (p=0.015, 95% CI: 0.032–0.277) between eyes-open and eyes-closed conditions. ML mean velocity also displayed a significant condition effect (p=0.025, 95% CI: 0.025–0.358). In contrast to the effect of visual input, there was no main effect of concussion history on these metrics. Conclusions A history of 3+ concussions does not appear to result in long-term deficits controlling in quiet stance. Those ML variables were sensitive to condition and indicate that frontal plane COP movements may be more sensitive than those in the sagittal plane. These findings are important as a history of concussion does not appear to alter quiet stance balance control mechanisms. Competing interests None.

Objective To examine the effects of concussion history on an index of cerebral autoregulation in a healthy athlete population. Design Retrospective Cohort. Setting Laboratory. Participants 136 male contact sport athletes (19.1±1.4 years, 66 football, 70 hockey) were recruited; 39 presented with 0 previous concussions, 16 with 3+ previous concussions; exclusion criteria included history of concussion within 6 months. Intervention Participants completed baseline testing prior to the athletic season. Squat-stand manoeuvres at 0.05 and 0.10 Hz were used to enhance blood pressure (BP) variation. BP and cerebral blood velocity (CBV) in the middle cerebral artery were indexed non-invasively via finger photoplethysmography and transcranial Doppler ultrasound, respectively. Independent variables included sport (2) and concussion history (2). Outcomes Transfer function analysis point estimates at 0.05 and 0.10 Hz characterised the coherence (correlation), phase (synchronisation), and gain (amplitude buffer) between BP and CBV waveforms during the squat-stand manoeuvres. Results These findings suggest that, despite reductions in 0.10 Hz phase lead being reported acutely after concussion, multiple concussions do not appear to induce long-term impairments in dynamic cerebral autoregulation metrics. This is an important revelation as it indicates that the cerebrovasculature is able to adequately recover following the acutely diminished buffering capacity associated with a concussive injury Conclusions These findings suggest that, despite reductions in 0.10 Hz phase lead being reported acutely after concussion, multiple concussions do not appear to induce long-term impairments in dynamic cerebral autoregulation metrics. This is an important revelation as it indicates that the cerebrovasculature is able to adequately recover following the acutely diminished buffering capacity associated with a concussive injury Competing interests None.

Objective To examine the effect of multiple previous concussions on heart rate variability (HRV) in contact-sport athletes. Design Retrospective Cohort. Setting Laboratory. Participants 136 male elite contact-sport (hockey and football) athletes were recruited for this study. Forty-one had no previous concussion history (Hx-), while nineteen had a history of three or more concussions (Hx+). All testing was preformed prior to the start of the competitive season Interventions HRV was assessed during 5-minutes of quiet stance, and while actively squatting at 0.10 Hz via a 3-lead electrocardiogram, using Kubios software. Independent variables included condition (rest vs active) and group (Hx+ vs Hx-) Outcome measures Time-Domain: square root of mean squared differences of successive R-R intervals (RMSSD), percentage of successive R-R intervals that differ by more than 50 milliseconds (pNN50). Frequency-Domain: total power. Main results Mixed ANOVA revealed repeated squat-stand manoeuvres challenged the autonomic system, increasing total power by 2477 milliseconds2 (95% CI: 1153–3801, p Conclusions A history of multiple sport-related concussions impairs the ability of the autonomic system to respond to an everyday stressor applied to the cardiovascular system (squatting and standing). This is an important finding, as it reveals that cumulative concussions may impart long-term impairments in the ability to accurately regulate the autonomic system. Competing interests None.

Objective To determine how a history of 3+ concussions alters elevations in cerebral blood velocity (CBV) in the posterior cerebral artery (PCA) during visual tasks. Design Retrospective Cohort. Setting Laboratory. Participants 136 male contact-sport athletes (19.1±1.4 years, 66 football, 70 hockey) were recruited; 39 presented with 0 previous concussions, 16 with 3+ previous concussions; exclusion criteria included history of concussion within 6 months. Intervention Transcranial Doppler ultrasound indexed PCA-CBV during a series of visual tasks. Participants closed their eyes (20-seconds) and, when prompted, opened their eyes to complete a visual task (40-seconds). Testing occurred prior to the start of their athletic season. The visual trial raw traces were averaged together to enhance the signal-to-noise ratio of outcome measurements. The independent variable tested was concussion history. Outcomes Eyes-closed CBV (cm/s), peak elevation in CBV after eyes-open (cm/s), relative change in CBV (%), and total activation during the first 30 seconds of the task (indexed via area under the curve-AUC) Main results Independent samples T-Tests indicated there were no effects of concussion history on any outcome: Eyes-closed CBV (p=0.950), peak CBV (p=0.903), % CBV elevation (p=0.593), and AUC (p=0.718). Conclusions A history of multiple concussions does not alter the cerebrovasculature’s ability to maintain nutrient delivery required for visual challenges in cortical areas supplied by the PCA. This is an important finding; despite the long-term neurocognitive deficits associated with a history of concussions, the transcranial Doppler assessment of neurovascular coupling appears intact for this population of younger adult contact-sport athletes. Competing interests None.

Objective To determinethe extentto which an acute sport-related concussion disrupts elevations in cerebral blood velocity (CBV) in the posterior cerebral artery (PCA) during visual tasks. Design Prospective Cohort. Setting Laboratory. Participants 136 male contact-sport athletes (19.1±1.4 years) recruited, subset of 14 participants (19±1.4 years) sustained concussions. Intervention Transcranial Doppler ultrasound was used to index CBV in the PCA during a series of visual tasks. Participants closed their eyes (20 seconds), and when prompted, opened their eyes and completed a visual task (40 seconds). Testing was completed prior to the start of their athletic season (T0), and again (if concussed) at 72-hours (T1), 2-weeks (T2), and 1-month (T3) post-injury. The raw traces from each trial were averaged to enhance the signal-to-noise ratio of the outcome measurements. Independent variable tested was time (4 points). Outcome measures Eyes-closed CBV (cm/s), peak elevation in CBV (cm/s), relative change in CBV (%) and total activation during the first 30 seconds of the task (indexed via area under the curve-AUC) Main results RM-ANOVA indicated there were no time effects forany of the outcome metrics: Eyes-closed CBV (p=0.473), peak CBV (p=0.541),% CBV elevation (p=0.603) and AUC (p=0.972). Conclusions These negative findings are important, as they indicate the PCA is able to maintain nutrient delivery required for visual challenges. Thus, neurovascular coupling is maintained despite the reported impairments in indices of cerebral autoregulation in the same population. Competing interests None.

Objective Examine how the frequency-dependent relationship between blood pressure (BP) and cerebral blood velocity (CBV) is affected by acute sport-related concussion. Design Prospective Cohort. Setting Laboratory. Participants: 136 male contact-sport athletes (19.1±1.4 years) recruited, subset of 14 sustained concussions (19±1.4 years). Intervention Participants completed baseline (T0) and post-injury testing at 72-hours (T1), 2-weeks (T2), and 1-month (T3). BP was monitored via finger photoplethysmography, and transcranial Doppler ultrasound indexed CBV in the middle cerebral artery. Squat-stand manoeuvers were performed at 0.05 and 0.10Hz to enhance BP variation. RM-ANOVA independent variables included time (4) and frequency (2). Outcome measures Transfer function analysis point estimates quantified coherence (correlation), phase (synchronisation) and gain (amplitude buffer) metrics between BP and CBV waveforms. Results Significant frequency-time interactions for phase (p=0.007) and gain (p=0.049). Simple effects analysis revealed time effects for phase at 0.10 Hz, indicating reductions at T1 (95% CI: 0.033 – 0.24 rads, p=0.008) and T2 (95% CI: 0.014–0.196 rads, p=0.02) compared to T0. On average, return-to-play occurred at T2 (median 14 days). Phase reductions at T1 were correlated with Standardised Assessment of Concussion performance (r=0.659, p=0.02). Conclusions These results reveal transient post-concussion impairments in the capacity of the cerebrovasculature to buffer BP oscillations, which exceeded clinical recovery duration. Phase reductions at 0.10Hz suggest the presence of a cerebrovascular autonomic dysregulation, which could leave the brain less protected to BP surges. This key finding may help explain why the brain is more vulnerable to additional trauma during the post-injury recovery period. Competing interests None.