Head Impact Exposure in College Football after a Reduction in Preseason Practices

Brian D. Stemper; Alok S. Shah; Jason P. Mihalik; Jaroslaw Harezlak; Steven Rowson; Stefan Duma; Larry D. Riggen; Alison Brooks; Kenneth L. Cameron; Christopher C. Giza; Joshua Goldman; Megan N. Houston; Jonathan Jackson; Gerald Mcginty; Steven P. Broglio; Thomas W. Mcallister; Michael Mccrea


Med Sci Sports Exerc. 2020;52(7):1629-1638. 

In This Article

Abstract and Introduction


Introduction: Regulatory efforts toward reducing concussion risk have begun to focus on decreasing the number of head impacts (i.e., head impact burden) sustained by athletes in contact sports. To that end, in 2018, the NCAA decreased the number of preseason on-field team activities for Division I teams from 29 to 25. The objective of the current study was to quantify changes in practice schedule and head impact exposure between the 2017 and 2018 football preseasons.

Methods: Athletes from five NCAA Division I football teams (n = 426) were consented and enrolled.

Results: On average, athletes participated in 10% fewer contact practices in 2018. However, the effect of this ruling on preseason head impact burden was mixed. Across all athletes, the total preseason head impact burden was essentially the same from 2017 to 2018. However, this study revealed significant team-by-team differences in preseason head impact burden, with one team demonstrating a 35% increase in the average number of recorded head impacts from 2017 to 2018, despite a modest decrease in the number of contact practices. Other teams had similar or decreased head impact burden.

Conclusions: Team-based differences in total preseason head impact burden were attributable to changes in daily practice schedule, with longer practice durations and more intense contact practice sessions contributing to increases in daily head impact exposure that, in turn, led to greater preseason head impact burden. Results of this study have highlighted the difficulty in decreasing contact sport head impact exposure through rule changes targeted at limiting on-field team activities. Future efforts aimed specifically at contact practice duration, daily head impact exposure, or limiting time in specific drills may be more effective at reducing total preseason head impact burden.


With an increased understanding of the high rate of concussion in amateur contact sports as well as the long-term consequences of repeated concussion,[1,2] efforts have begun to focus on rule changes by governing bodies that can reduce concussion risk for participating athletes. For example, after a report of elevated concussion risk during football kickoff returns,[3] the NCAA Ivy League moved the kickoff from the 35- to the 40-yard line to increase the number of touchback plays, wherein the kickoff play ends without significant contact between opposing teams. This rule change resulted in more than a twofold increase in the number of touchbacks and a decrease in the rate of concussion during kickoffs to less than 20% of what it was before the rule change.[4] A similar rule change in the NFL, wherein the kickoff restraining line was moved from the 30- to the 35-yard line to reduce the distance between kicking and receiving teams, had mixed results with a nonsignificant trend of decreasing incidence of head injuries during kickoff plays when the ball was returned.[5] These efforts by the Ivy League were consistent with its focus on reducing concussion risk as evidenced by additional rule changes to eliminate tackling in practices during the regular season and reducing the total number of preseason practices.[6] However, to our knowledge, the effect of those rule changes on the rate of concussion in the Ivy League has not yet been reported.

Although the above-discussed kickoff rule changes were associated with somewhat measurable decreases in concussion incidence, kickoffs account for only 6% of plays during a football game.[4] Therefore, significant additional rulemaking opportunities exist to decrease concussion risk because kickoffs account for such a small percentage of the plays during a football game and contact practices account for a the highest percentage of an athlete's season-long head impact exposure.[7,8] Approximately one half of all football-related concussions occur during practice,[9] and some evidence exists to indicate that concussion incidence may be biased toward the preseason.[10] Additionally, rule changes affecting practice schedule and characteristics represent an opportunity to decrease head impact burden and concussion risk in contact sports without fundamentally changing the rules of game play. Accordingly, the NCAA implemented a rule change to eliminate two-a-day practices during the 2017 fall football preseason.[11] That rule change maintained the number of allowable preseason on-field practice sessions at 29, with two-a-day practices counting as two on-field practice sessions in 2016. However, because the total number of on-field practice sessions remained consistent from 2016 to 2017, preseason head impact exposure and concussion incidence actually increased in a sample of five Division I programs during the 2017 season.[7] The NCAA acted again in 2018 to reduce the total number of allowable preseason on-field practices from 29 to 25.[12] The objective of this analysis was to compare preseason head impact exposure and the characteristics of contact practices between the 2017 and 2018 fall preseasons to delineate the overall effect of decreasing the allowable number of contact practices. Our hypothesis was that the NCAA ruling to reduce the number of preseason on-field practices would reduce the overall preseason head impact burden (i.e., total number of head impacts) for participating athletes.