title: Measurement of head impacts in collegiate football players: an investigation of positional and event-type differences.
abstract: OBJECTIVE
  There 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.
  
  
  METHODS
  We 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 chi tests of association assessed positional, event type, and location of head impact differences.
  
  
  RESULTS
  Football 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.
  
  
  CONCLUSIONS
  Less 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.
authors.affiliation: Department of Exercise and Sport Science, Curriculum in Human Movement Science, The University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Jason P
authors.initials: JP
authors.lastname: Mihalik
authors.forename: David R
authors.initials: DR
authors.lastname: Bell
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Marshall
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Guskiewicz
mesh_terms: D000054:Acceleration; D000293:Adolescent; D000328:Adult; D001265:Athletic Injuries / Q000209:etiology*; D001696:Biomechanical Phenomena; D001924:Brain Concussion / Q000209:etiology* / Q000473:pathology*; D005538:Football; D006260:Head Protective Devices; D006801:Humans; D008297:Male; D010812:Physical Stimulation; D011446:Prospective Studies; D012189:Retrospective Studies; D018570:Risk Assessment; D014495:Universities