Effect of sport-related concussion on clinicallymeasured simple reaction timeJames T Eckner,1,2 Jeffrey S Kutcher,2,3 Steven P Broglio,2,4 James K Richardson1

▸ Additional material ispublished online only. To viewplease visit the journal online(http://dx.doi.org/10.1136/bjsports-2012-091579).1Department of PhysicalMedicine & Rehabilitation,University of Michigan,Ann Arbor, Michigan, USA2Michigan NeuroSport,University of Michigan, AnnArbor, Michigan, USA3Department of Neurology,University of Michigan,Ann Arbor, Michigan, USA4School of Kinesiology,University of Michigan,Ann Arbor, Michigan, USA

Correspondence toJames T Eckner,Department of PhysicalMedicine & Rehabilitation,University of Michigan, 325 E,Eisenhower Pkwy, Ann Arbor,MI 48108, USA;jeckner@med.umich.edu

Received 16 July 2012Revised 19 October 2012Accepted 4 December 2012Published Online First11 January 2013

To cite: Eckner JT,Kutcher JS, Broglio SP, et al.Br J Sports Med2014;48:112–118.

ABSTRACTBackground Reaction time (RT) is a valuablecomponent of the sport concussion assessment battery.RT is typically measured using computers runningspecialised software, which limits its applicability insome athletic settings and populations. To address this,we developed a simple clinical test of RT (RTclin) thatinvolves grasping a falling measuring stick.Purpose To determine the effect of concussion onRTclin 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 within48 h of injury. Repeated measures analysis of variancecompared mean baseline and follow-up RTclin valuesbetween groups. Sensitivity and specificity werecalculated over a range of reliable change confidencelevels.Results RTclin differed significantly between groups(p<0.001): there was significant prolongation frombaseline to postinjury in the concussed group(p=0.003), with a trend towards improvement in thecontrol group (p=0.058). Sensitivity and specificity weremaximised when a critical change value of 0 ms wasapplied (ie, any increase in RTclin from baseline wasinterpreted as abnormal), which corresponded to asensitivity of 75%, specificity of 68% and a 65%reliable change confidence level.Conclusions RTclin appears sensitive to the effects ofconcussion and distinguished concussed and non-concussed athletes with similar sensitivity and specificityto other commonly used concussion assessment tools.Given its simplicity, low cost and minimal timerequirement, RTclin should be considered a viablecomponent of the sports medicine provider’smultifaceted concussion assessment battery.

INTRODUCTIONSport-related concussion (SRC) is common1 andthere is increasing concern regarding possible long-term effects.2–4 While concussed athletes typicallyrecover symptomatically within 1–2 weeks,5 6 anathlete whose concussion is unrecognised or whoreturns to play prematurely is put at risk for moresignificant injury.7 Thus, prompt recognition ofSRC and accurate determination of its resolutionare important. However, SRC remains a diagnosticchallenge. Presentations are variable and oftensubtle, and athletes may minimise their symptoms.8

While a growing number of assessment tools havebeen developed, the diagnosis of SRC remains aclinical one.Current consensus opinion advocates a multifa-

ceted approach to concussion assessment.9–11

Clinical tools are available to evaluate many aspects

of concussion including symptoms,12 neurocogni-tive function13 and balance.14 Computer-basedneurocognitive assessment tools capable of measur-ing reaction time (RT), attention, working memoryand problem solving are also available.15–17 Suchtools can be valuable, but their computer-dependence, time requirement and cost limit theirapplicability in some situations (eg, acute concus-sion diagnosis) and environments (eg, communitieswith limited financial resources).A prolonged RT is common following SRC, and

is one of the most sensitive indices of neurocognitivechange following injury.18 19 In addition RT hasbeen shown to have prognostic value20 and com-monly parallels other concussion symptoms.21–24

Moreover, a prolonged RT can persist beyondsymptom resolution, suggesting incremental valueover solely tracking postconcussive symptoms.5 25 26

Despite these advantages, computer-independentmethods for assessing RT are not available. Toaddress this, we developed a simple, inexpensivemethod for clinically assessing RT, referred to asclinical RT (RTclin). RTclin is a visuomotor test inwhich the subject arrests a falling object by handclosure after it is released by an examiner. Pilotwork demonstrated the short-term and long-termreliability of RTclin,27 28 and its validity with rela-tion to a computerised measure or RT in athletes.29

Furthermore, the task appears to be intrinsicallymotivating,30 an important characteristic for situa-tions in which an athlete’s after-injury performanceis compared to preseason baseline.31 Unlike othertests of RT, RTclin has demonstrated functional rele-vance by showing a strong correlation with an ath-lete’s ability to protect their head in a laboratorysimulated athletic environment.32 Recently, wereported a 13.5% prolongation of RTclin in ninecollegiate athletes tested within 72 h of SRC ascompared with baseline.33 Although the results aresuggestive, a larger, controlled study is needed tofurther elucidate the clinical usefulness of RTclin.Therefore, the purpose of this study is to determinethe effect of concussion on RTclin in a largersample of high school and collegiate athletesthrough a controlled study design. We hypothesisedthat RTclin would be prolonged in concussed ath-letes as compared to baseline and non-concussedcontrol athletes.

METHODSSubjectsMale and female athletes participating in multiplesports at two universities and one high school wererecruited during preparticipation physical examina-tions over two consecutive seasons. Potential sub-jects were excluded if they were recovering from a

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concussion or had an upper limb injury preventing the comple-tion of the RTclin task. Adult athletes provided institutionalreview board (IRB) approved informed written consent andminor athletes provided IRB-approved assent with accompany-ing parental consent. For the purposes of this study, concussionwas diagnosed by the athlete’s treating physician as defined inthe 2008 Zurich Consensus Statement on Concussion in Sport.9

Testing scheduleRTclin was measured in all athletes at baseline during prepartici-pation examinations. RTclin was determined again within 48 hof injury in athletes who sustained a physician-diagnosed con-cussion. For each injured athlete, a control athlete was who wasa member of the same team and was present in the trainingroom for a reason other than concussion was also retested.Athletes with a dominant upper limb injury preventing comple-tion of the RTclin task were again excluded, analogous to duringbaseline testing.

Measuring RTclinThe protocol for RTclin testing has been previously described28 29

and is illustrated in figure 1. The RTclin apparatus is an 80 cmrigid measuring stick coated in friction tape with a weightedrubber disk affixed to one end. Athletes sat with their dominantforearm resting on a table with their hand positioned over itsedge. The hand was open surrounding, without touching, theweighted disk portion of the RTclin apparatus. The examinersuspended the device vertically such that the top face of the diskwas aligned in the plane defined by the top of the athlete’s openhand. After predetermined randomly assigned delays rangingfrom 2 to 5 s, the examiner released the apparatus and theathlete caught it as quickly as possible by hand closure. For eachtrial, an RTclin value (in ms) was calculated from the distance (incm) that the device fell using the formula for a body fallingunder the influence of gravity (d=0.5 gt2). After two practicetrials, each athlete completed eight data acquisition trials and amean RTclin value was calculated for the test session. The meanRTclin value was used for analysis. RTclin change scores were

determined by the difference between baseline and follow-upvalues (follow-up RTclin−baseline RTclin) so that a positive RTclinchange score represents a decline from baseline, while a negativescore represents improvement.

Data analysisA two-way repeated measures analysis of variance, with pairedt tests used post hoc, was used to compare preseason and after-injury RTclin values in concussed versus control athletes. Theeffect sizes of the RTclin changes observed were described usingCohen’s d. Reliable change calculations were performed usingSDs of difference scores (SDdiff ) from the control group.34

An adjusted reliable change equation, controlling for practiceeffects,35 was used:

RC ¼ ½ðx2 $ x1Þ $ ðm2 $ m1Þ&=SDdiff

where x2−x1 is the individual performance difference betweenfollow-up (x2) and baseline (x1) RTclin in a concussed athlete;μ2−μ1 is the mean group difference between follow-up (μ2) andbaseline (μ1) RTclin in the control group; and SDdiff is the SD ofthe change scores for the control group. An adjusted reliablechange index has been demonstrated to perform comparably tomore complex regression-based formulas36–38 and has beenadvocated over regression-based methods.36

Reliable change values can be interpreted by comparing themto the z-distribution critical value associated with a desired one-tailed probability of error. One-tailed critical values were usedbecause the outcome of interest was a decline in performancefrom baseline, rather than any difference, which could representeither decline or improvement.39 40 For example, a critical valueof 1.65 is used when a 5% type I error rate is deemed accept-able. Therefore a reliable change score greater than 1.65 can beinterpreted as an indication that an athlete has experienced asignificant decline in their RTclin performance, with a 5% prob-ability of type I error.

Conversely, once the mean RTclin change score and its asso-ciated SD are calculated in the control group, a cut-off valuecan be generated indicating the RTclin change score that

Figure 1 Demonstration of theclinical reaction time device andprocedure.

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represents significant change at a given level of confidence. Wecalculated reliable change cut-off values over a range of confi-dence levels and determine the combined sensitivity and specifi-city associated with each value.41 In addition, a receiveroperating characteristic curve (ROC curve) was generated tocompare the sensitivity and specificity associated with cut-offvalue over the range of RTclin change scores observed.Sensitivity and specificity values were summed at each cut-offvalue, with the highest summed score interpreted as having thegreatest combined sensitivity and specificity.41 42

RESULTSTwenty-six athletes sustained 28 concussions (with two athletessustaining repeat concussions) over the 2-year study. The major-ity of concussions occurred in male collegiate football players(n=20, 71.4%). The remaining injuries were sustained by ath-letes participating in male high school football (n=2, 7.1%),female collegiate soccer (n=2, 7.1%), male collegiate ice hockey(n=1, 3.6%) and male high school ice hockey (n=1, 3.6%). Ofnote, two injuries which occurred during year 2 involved ath-letes who did not have baseline RTclin results available from thatyear. Therefore, year 1 baseline RTclin results were used forthese subjects and for their matched controls. Eight of the post-concussion testing sessions were completed on the day of injury,

12 were completed 1 day after injury and eight were completed2 days after injury not exceeding 48 h. All concussed athleteswere still reporting postconcussion symptoms at the time oftesting. The time from baseline to follow-up RTclin testing didnot differ between the concussed and control groups (mean±SD=60.5±40.5 and 73.8±51.0 days, respectively; p=0.631).

Concussed and control athletes demonstrated nearly identicalmean (±SD) baseline RTclin values (203±22 ms vs 202±16 ms,respectively; p=0.839). After-injury RTclin values were signifi-cantly greater (longer) as compared with baseline (220±29 ms;p=0.003; effect size, d=0.616), while there was a trendtowards shorter RTclin values in the 28 controls (193±17 ms,p=0.058; effect size, d=−0.373). The group by test interactionwas highly significant (p<0.001). The contrast between baselineand follow-up RTclin in the two groups is illustrated in figure 2.

Reliable change cut-off values for RTclin and the associated sensi-tivity and specificity at each confidence level are presented intable 1. The cut-off values represent the RTclin change values neces-sary to conclude that an athlete has experienced a significant pro-longation in RTclin at a given level of confidence. An ROC curvecomparing the sensitivity and specificity of RTclin at every possiblecut-off value over the observed range of RTclin change values wasalso generated (figure 3). Resulting analysis demonstrated thatcut-off values from 0 to −2 ms (ie, 2 ms of improvement at

Figure 2 Change in mean clinical reaction time in concussion and control groups. Solid line represents concussion group; dotted line representscontrols. Error bars represent standard error.

Table 1 Reliable change cut-off values for RTclin at a variety of confidence levels with the number of concussed and control subjects whodemonstrated greater decline than the cut-off value as well as the corresponding sensitivity and specificity of the RTclin test at each confidencelevel

Confidence level (%) Critical value* RTclin cut-off value (ms) Concussed subjects Control subjects Sensitivity Specificity Combined sens+spec

95 1.65 30.6 11 2 0.39 0.93 1.3290 1.28 21.7 14 4 0.50 0.86 1.3680 0.84 11.2 16 6 0.57 0.79 1.3670 0.052 3.5 18 9 0.64 0.68 1.3260 0.25 −3.0 22 11 0.79 0.61 1.40

*Critical values represent the one-sided z-score associated with each level of confidence.RT, reaction time.

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follow-up) maximised sensitivity and specificity of RTclin with acombined value of 1.43. This corresponds to a critical value of0.375 and an associated one-sided confidence level of 65%.

DISCUSSIONIn this study we observed a significant decline in RTclin perform-ance following SRC in a group of 28 concussed athletes (8.4%slower RT). These results are similar to those previouslyreported.33 The effect size reported here is generally consideredto be moderate in size.43 In contrast, follow-up RTclin perform-ance showed a trend towards improvement in the control ath-letes. Group analyses showed that the contrast betweenpostinjury performance declines observed in the injured athletesversus the improvement in controls was highly significant.

Reliable change analyses allow group data to be applied toindividuals. We found that to be 95% confident an athlete’sRTclin performance has declined, RTclin must be at least 31 msslower during follow-up testing. Using this cut-off value correctlyidentifies 11 of the 28 concussed athletes studied (39% sensitiv-ity), but it incorrectly identifies just 2 of the 28 control athletes ashaving performed worse (93% specificity). Conversely, if wechoose to be 60% confident that an athlete’s follow-up RTclinperformance is worse the cut-off value is 3 ms improvementfrom baseline, due to the non-concussed athletes having fasterRTclin at follow-up. These control athlete data suggest a smalllearning effect, consistent with prior observations.27 Using this3 ms improvement cut-off value correctly identifies 22 of the 28concussed athletes (79% sensitivity), while incorrectly identifying11 of the 28 control athletes (61% specificity).

Screening tests should have high sensitivity so as to identifythe majority of affected individuals. Given the inherent trade-offbetween sensitivity and specificity, an increased sensitivity invari-ably results in an increased false-positive rate. However, giventhe current ‘when in doubt sit them out’ approach with regardto concussion, this trade off seems appropriate. This is especiallytrue in younger athletes, where the consequences of a missed

injury are greatest.7 Moreover, maximising test sensitivity at theexpense of specificity has been advocated by other groups withregard to concussion assessment tools.42 44–47 In our study, achange score of 0 ms (ie, interpreting any follow-up RTclinvalue, that is, slower than baseline as abnormal) was found tomaximise the combined sensitivity (75%) and specificity (68%)of the test and correlated with a reliable change confidence levelof 65%. Therefore we propose an RTclin cut-off value of 0 msbe used when screening an athlete with suspected concussion.

The test characteristics for RTclin reported here are similar toother recognised concussion assessment tools. For example,McCrea et al47 reported on the sensitivity and specificity offour commonly used assessment tools. Test sensitivities werehighest when testing occurred within 3 h of injury, with theGraded Symptom Checklist (GSC) being the most sensitive(89% sensitive, 100% specific), followed by the StandardizedAssessment of Concussion (SAC; 80% sensitive, 91% specific),and the Balance Error Scoring System (BESS; 34% sensitive,91% specific). The neuropsychological test battery administered2 days following injury had a sensitivity and specificity of 23%and 93%. At the same 2 day postinjury interval the sensitivity/specificity of the GSC, SAC and BESS dropped substantially to27%/100%, 22%/89% and 24%/91%, respectively. Overall amarked reduction in sensitivity was observed for each test overthe first week following injury. The authors also noted that com-binations of tests had greater sensitivity than individual tests.Broglio et al48 later reported on the sensitivity of five differentconcussion assessment tools.48 The most sensitive measure wasthe Immediate Post-concussion Assessment Cognitive Test(ImPACT; 79.2%), with its most sensitive component being thesymptom inventory (62.5%). The combined sensitivity of theremainder of the ImPACT battery was 62.5%, with the memoryand RT composite scores being the most sensitive individualtests (41.7% each). The overall sensitivity of the HeadMinderConcussion Resolution Index was 78.6%, with individual testcomponent sensitivities of 71.4% for simple and complex RTand 50% for processing speed. A nine item concussionsymptom scale was the next most sensitive tool (68%). As wasthe case in McCrea’s study, test batteries demonstrated greatersensitivity than any single component used in isolation. The spe-cificities of these tests were not reported. Other relevant studiesin this regard are summarised in table 2.

In aggregate, the sensitivity and specificity of concussionassessment tools are greater when the test is conducted immedi-ately following injury, with a gradual decline in sensitivity overtime. It also appears that test batteries with multiple componentsare more sensitive than individual measures. With these consid-erations in mind, it is remarkable that RTclin, a single 5 min testthat was performed up to 48 h after injury with equipmentcosting less than five US dollars, has comparable test characteris-tics to other concussion assessment tools currently in use, includ-ing lengthier computerised neuropsychological test batteriescomposed of multiple individual tests (eg, ImPACT and CRI),traditional paper and pencil neuropsychological test batteries(composed of the HVLT, TMT, SDMT, DS, COWATand Stroop),and costly balance assessment tools (eg, SOT). Further researchshould evaluate the test characteristics of a concussion assessmentbattery composed entirely of clinical assessment tools such as asymptom checklist, the SAC, RTclin and the BESS. Such a batteryis likely to have improved sensitivity over its individual compo-nent measures, and could easily be used by sports medicine provi-ders in nearly any location at minimal expense.

The control athletes represent one of the study’s strengths.These athletes were retested at similar time intervals as their

Figure 3 Receiver operating characteristic curve for the clinicalreaction time test. Open markers represent cut-off change scores of 0and −2 ms, where combined sensitivity and specificity weremaximised.

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Table 2 Summary of relevant literature reporting on the test sensitivity and specificity of sport concussion assessment tools

Reference Study population Test admin. time Test(s) administered Number of cases Number of controls Sensitivity (%) Specificity (%) Combined sens+spec

Barr and McCrea42* HS & college Immediately SAC 50 68 94 76 1.70Erlanger et al46† HS & college 1.96±1.5 day CRI battery 26 0 77 n/a n/a

Processing speed index 19Simple RT index 38Complex RT index 54

6.15±4.0 day CRI battery 18 0 50 n/a n/aPS index 11SRT index 28CRT index 28

Iverson et al45‡ HS & college < 72 h ImPACT battery 41 56 76 63 1.39Symptoms 54 88 1.42Verbal memory 44 89 1.33Visual memory 42 89 1.31Reaction time 51 91 1.42Processing speed 42 93 1.35

McCrea et al47§ College Immediately GSC 94 56 89 100 1.89SAC 80 91 1.71BESS 34 91 1.25

2–3 h GSC § § 74 100 1.74SAC 65 93 1.58BESS 31 96 1.27

1 day GSC § § 53 100 1.53SAC 31 95 1.26BESS 16 93 1.09

2 day GSC § § 27 100 1.27SAC 22 89 1.11BESS 24 91 1.15NP battery§ 23 93 1.16

3 day GSC § § 20 100 1.20SAC 18 93 1.11BESS 16 91 1.07

5 day GSC § § 10 100 1.10SAC 18 93 1.11BESS 10 93 1.03

7 day GSC § § 4 100 1.04SAC 2 98 1.00BESS 7 95 1.02NP battery§ 19 91 1.10

Schatz et al49¶ HS <72 h ImPACT battery 72 66 82 89 1.71Broglio et al48** College <24 h Concussion symptom inventory 75 0 68 n/a n/a

ImPACT battery 24 0 79 n/a n/aSymptom inventory 63Verbal memory 42Visual memory 21Visual motor speed 21Reaction time 42Impulse control 4

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Table 2 Continued

Reference Study population Test admin. time Test(s) administered Number of cases Number of controls Sensitivity (%) Specificity (%) Combined sens+spec

CRI battery 28 0 78.6 n/a n/aProcessing speed index 50Simple RT index 71Complex RT index 71

SOT 63 0 62 n/a n/aComposite balance 37Somatosensory ratio 37Visual ratio 32Vestibular ratio 24

NP battery** 23 0 43.5 n/a n/aBroglio et al41†† College <24 h SOT battery 63 66 57 80 1.38

Composite balance 44 91 1.35Somatosensory ratio 11 91 1.02Visual ratio 18 89 1.07Vestibular ratio 24 96 1.19

Eckner et al (2013)‡‡ HS & college <48 h RTclin 28 28 75 68 1.43

*Based on classification of a one-point decline from baseline as abnormal.† Regression-based analysis classifying impaired (5th percentile) and borderline (5th–15th percentile) performance as abnormal.‡Based on reliable change index adjusted for practice effects at 80% confidence level.§Regression-based analysis employing a 90% CI for GSC, SAC, and BESS. Individual components of NP battery included HVLT Immediate Memory, HVLT Delayed Recall, HVLT Recognition, Trail Marking Test (Part B), SDMT, Stroop CW Trial and COWAT;significantly decreased score on 2 or more components was considered abnormal. Attrition rates at each follow-up time point not directly reported.¶Based on a stepwise discriminant analysis including postconcussion symptom checklist, processing speed composite, visual memory composite and impulse control composite scores. Results of an analysis including the verbal memory and reaction timecomposite scores, as well as the sensitivities/specificities associated with the individual test components are not presented.**Concussion symptom inventory was classified as abnormal when a 1 SD increase above baseline symptom severity and/or duration score was present. Significant declines in ImPACT and CRI scores were interpreted based on the reliable change indexscore calculations embedded within each programme. SOT variables were classified as abnormal when a 1 SD decline from baseline was present. Individual components of the NP battery included the HVLT, TMT (Parts A and B), SDMT, DST and COWAT;a 1 SD decline in two or more components was considered abnormal.††Based on a reliable change index adjusted for practice effects at 75% confidence level.‡‡Results presented herein based on reliable change index adjusted for practice effects at 65% confidence level.ImPACT, Immediate Post-concussion Assessment Cognitive Test; RT, reaction time; SAC, Standardized Assessment of Concussion.

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concussed team-mates and were typically receiving treatment fornon-concussive injuries at the time of follow-up assessment.This is important and suggests that the concussed athletes’altered RTclin performance is more likely related to their concus-sions than to other in-season factors affecting the team thatwere not measured or directly controlled for in our studydesign. In addition, the results are more compelling given priorwork finding RTclin to be valid, intrinsically motivating andfunctionally relevant.27–30 32 The study also has limitations thatmerit discussion. The majority of concussed athletes were malecollegiate football players, and so the generalisability of thisstudy’s findings to other populations is uncertain. Also, the ath-letes underwent after-injury testing at a single time point within48 h of concussion, and so no information regarding a postin-jury ‘recovery curve’ is available. Furthermore, since additionalconvergent and divergent measures were not simultaneouslyassessed during this study and final athlete outcomes were notrecorded, this study does not fully address the convergent,divergent or predictive validity of RTclin for concussion. In add-ition, in some cases the follow-up tests on control athletes werenot conducted on the exact same day as the after-injury tests intheir concussed team-mates. We do not suspect that these gener-ally small differences in time until follow-up testing have intro-duced significant bias, however their effect is not known.Finally, examiners were not blinded to athletes’ concussionstatus during follow-up testing and so the introduction of meas-urement bias is possible. This is less likely given the nature ofthe task, which occurs on a millisecond scale, and given thatexaminers were not aware of the athlete’s baseline performance.

In conclusion, the results suggest that RTclin performance isimpaired following concussion, while in-season follow-up RTclintesting of non-concussed (but often injured) control athletes isassociated with a small learning effect. Reliable change calcula-tions indicate that a critical RTclin change score of 0 ms (ie,interpreting any decline from baseline as indicative of impair-ment) is 75% sensitive and 68% specific for concussion. Thesetest characteristics compare favourably with most currently avail-able concussion assessment tools, many of which are associatedwith significantly more time, equipment, and expense thanRTclin. Furthermore, RTclin may have even greater utility whenused as part of a concussion assessment battery, in concert witha symptom assessment, and clinical cognitive and balance assess-ments. RTclin, like any concussion assessment tool, cannot diag-nose concussion in isolation and must be interpreted by aknowledgeable sports medicine provider in the greater clinicalcontext of the athlete being assessed. The results of this studysupport the potential use of RTclin as part of a multifaceted clin-ical concussion assessment battery.

New findings

▸ In this study, clinically measured reaction time (RT)distinguished between concussed and non-concussedathletes.

▸ When any increase in clinically measured RT compared withthe athlete’s own baseline was considered abnormal (ie, acritical cut-off value of 0 ms was used), the test sensitivityand specificity were 75% and 68%, respectively.

▸ These findings support the use of clinically measured RT aspart a multifaceted sports medicine concussion assessmentbattery.

Acknowledgements The authors would like to thank all of the athletic trainers,team physicians, residents and students at Eastern Michigan University, theUniversity of Michigan, and Ann Arbor Skyline and Pioneer High Schools whoassisted with data collection for this study. Special thanks go to Steve Nordwall,Paul Schmidt, Rick Bancroft, Lenny Navitskis, Phil Johnson, Melissa Pohorence, BillShinavier, Jennifer Garcia, Dave Cotner, Allyson Calhoun, Nate Santoni, ShaileshReddy, Andy Schuldt and Tyler Ladue. We would also like to thank all of theathletes and coaches whose teams participated in this study. Dr Eckner also thanksthe Rehabilitation Medicine Scientist Training Program for its support of his effort onthis project through a K-12 career development award.

Contributors Dr JTE contributed to the study conception and design, as well asthe analysis and interpretation of data. He drafted the article and provided finalapproval of the submitted manuscript. Dr JSK contributed to the study conceptionand design, as well as the interpretation of data. He revised the article critically forimportant intellectual content and provided final approval of the submittedmanuscript. Dr SPB contributed to the analysis and interpretation of data. He revisedthe article critically for important intellectual content and provided final approval ofthe submitted manuscript. Dr JKR contributed to the study conception and design,as well as the analysis and interpretation of data. He revised the article critically forimportant intellectual content and provided final approval of the submittedmanuscript.

Funding Dr Eckner received a K-12 career development award from theRehabilitation Medicine Scientist Training Program which supported his effort on thisproject (grant number 5K12HD001097).

Competing interests An ICMJE conflict of interest form has been submitted byeach author.

Ethics approval University of Michigan-IRBMED.

Provenance and peer review Not commissioned; externally peer reviewed.

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Original article

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clinically measured simple reaction timeEffect of sport-related concussion on

RichardsonJames T Eckner, Jeffrey S Kutcher, Steven P Broglio and James K

doi: 10.1136/bjsports-2012-0915792013

2014 48: 112-118 originally published online January 11,Br J Sports Med

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