title: Estimation of head impact exposure in high school football: implications for regulating contact practices.
abstract: BACKGROUND
  Increased attention is being placed on the role of subconcussive impacts to the head during football participation and long-term cognitive health. Some have suggested that mitigating impacts to the head can be achieved by reducing or eliminating contact football practices. The effect that this might have on the number and magnitude of impacts is unknown.
  
  
  OBJECTIVE
  To estimate the effect of limiting contact practices on the frequency and magnitude of head impacts through the retrospective assessment of in vivo head impact data.
  
  
  METHODS
  Cross-sectional study; Level of evidence, 3.
  
  
  METHODS
  Data on impact magnitude and frequency were collected with the Head Impact Telemetry System during the 2009 football season among 42 varsity high school football athletes (mean age, 16.2 ± 0.6 years; mean height, 180.9 ± 7.2 cm; mean weight, 89.8 ± 20.1 kg). Head impacts were compared between player positions and session types (noncontact practice, contact practice, and game). These results were used to estimate the frequency and magnitude of head impacts when contact sessions were restricted.
  
  
  RESULTS
  The participants collectively sustained 32,510 impacts over the 15-week season. The typical athlete sustained a mean of 774 ± 502 impacts during the season, with linemen (center, guard, and offensive or defensive tackle positions) sustaining the highest number of impacts per athlete (1076 ± 541), followed by tight ends, running backs, and linebackers (779 ± 286); wide receivers, cornerbacks, and safeties (417 ± 266); and quarterbacks (356 ± 433). When viewed by session type, noncontact practices (n = 21) accounted for 1998 total impacts (2.4 ± 1.4 per athlete per session), contact practices (n = 36) accounted for 16,346 impacts (10.5 ± 7.7 per athlete per session), and games (n = 14) accounted for 14,166 impacts (24.1 ± 19.1 per athlete per session). Significantly more impacts occurred during games when compared with contact (P = .02) and noncontact practices (P < .001), and contact practices yielded significantly more impacts than noncontact practices (P = .02). Limiting contact practices to once per week would result in a 18% reduction in impacts for the duration of a season, while eliminating all contact practices would further reduce seasonal impacts by 39% across all players. Impact magnitudes were significantly highest during game sessions compared with contact and noncontact practices.
  
  
  CONCLUSIONS
  Our findings suggest that limiting or eliminating contact football practices may reduce the number of head impacts sustained by athletes over the course of a season, although the effect that such rule changes may have on the magnitude of head impacts during practice sessions is less clear. As such, the potential effect of reductions in contact practices on athletes' long-term cerebral health remains unknown.
authors.affiliation: Steven P. Broglio, ATC, NeuroSport Research Laboratory, University of Michigan, 401 Washtenaw Avenue, Ann Arbor, MI 48109. broglio@umich.edu.
authors.forename: Steven P
authors.initials: SP
authors.lastname: Broglio
authors.forename: Douglas
authors.initials: D
authors.lastname: Martini
authors.forename: Luke
authors.initials: L
authors.lastname: Kasper
authors.forename: James T
authors.initials: JT
authors.lastname: Eckner
authors.forename: Jeffery S
authors.initials: JS
authors.lastname: Kutcher
mesh_terms: D000054:Acceleration; D000293:Adolescent; D056352:Athletes; D001265:Athletic Injuries / Q000150:complications / Q000517:prevention & control*; D003072:Cognition Disorders / Q000209:etiology / Q000517:prevention & control; D006259:Craniocerebral Trauma / Q000150:complications / Q000517:prevention & control*; D003430:Cross-Sectional Studies; D005538:Football; D006260:Head Protective Devices; D006801:Humans; D008297:Male; D012189:Retrospective Studies; D012574:Schools; D013686:Telemetry
keywords: football (American); head injuries/concussions; impact frequency; impact magnitude