title: Head impact exposure sustained by football players on days of diagnosed concussion.
abstract: OBJECTIVE
  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.
authors.affiliation: Simbex, Lebanon, NH 03766, USA. jbeckwith@simbex.com
authors.forename: Jonathan G
authors.initials: JG
authors.lastname: Beckwith
authors.forename: Richard M
authors.initials: RM
authors.lastname: Greenwald
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Chu
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Crisco
authors.forename: Steven
authors.initials: S
authors.lastname: Rowson
authors.forename: Stefan M
authors.initials: SM
authors.lastname: Duma
authors.forename: Steven P
authors.initials: SP
authors.lastname: Broglio
authors.forename: Thomas W
authors.initials: TW
authors.lastname: McAllister
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Guskiewicz
authors.forename: Jason P
authors.initials: JP
authors.lastname: Mihalik
authors.forename: Scott
authors.initials: S
authors.lastname: Anderson
authors.forename: Brock
authors.initials: B
authors.lastname: Schnebel
authors.forename: P Gunnar
authors.initials: PG
authors.lastname: Brolinson
authors.forename: Michael W
authors.initials: MW
authors.lastname: Collins
mesh_terms: D000293:Adolescent; D001696:Biomechanical Phenomena; D001924:Brain Concussion / Q000175:diagnosis* / Q000453:epidemiology; D016001:Confidence Intervals; D005538:Football / Q000293:injuries* / Q000706:statistics & numerical data; D016489:Head Injuries, Closed / Q000453:epidemiology*; D006801:Humans; D008297:Male; D016017:Odds Ratio; D012372:ROC Curve; D015599:Trauma Severity Indices; D014481:United States / Q000453:epidemiology; D055815:Young Adult