Limiting Contact Practices In High School Football: Proceed With Caution, Study Concludes

Study details

To determine the effect policies to limit full-contact practices may have on the number and magnitude of head impacts at the high school level, Broglio and his colleagues evaluated impact data collected as part of an ongoing investigation of head impact biomechanics in high school football, selecting data from the 2009 season, as it was believed to represent the maximum season length for high school football: 7 days of preseason practice, including a scrimmage, 9 weeks of the regular season (2 noncontact practice sessions, 2 contact practice sessions, and 1 game), and 5 weeks of postseason play (1 noncontact practice, 3 contact practices, and 1 game) including the state championship game.

Analyzing the data collected using 1-year-old Riddell Revolution helmets equipped with the HITS system, an array of 6 single-axis accelerometers used to track and record linear and rotational acceleration, impact location and HITsp value (a unit-less measure of impact magnitude incorporating linear and rotational acceleration, impact location, impact duration using a weighted formula), Broglio and his colleagues at the University of Michigan found that:

• across all positions and including all session types, the typical high school football player sustained a mean of 774 ± 502 impacts during the season, or approximately 50 impacts per athlete per week;
• During the regular season, the typical athlete sustained:
  • 4 impacts above a 14.4 g linear acceleration threshold during 2 noncontact sessions (Monday and Thursday);
  • 22 impacts from 2 contact sessions (Tuesday and Wednesday), and
  • 24 impacts from a game (Friday).  
• In terms of impacts by position:
  • Lineman sustained the highest number of impacts per athlete (1076 ± 541), followed by
  • The tight end/running back/linebacker (TE/RB/LB) group (779 ± 286)
  • The wide receiver/cornerback/safety (WR/CB/S) group (417 ±  266) and
  • Quarterbacks (356  ± 431). 
• In terms of the number of head impacts during practice sessions, the numbers of impacts sustained by high school athletes was similar to those sustained by collegiate players, but high school athletes sustained nearly twice as many impacts, across all positions, during games as their collegiate counterparts, which the researchers said could be attributed to decreased player availability at the high school level, and fewer substitutions (i.e. more two-way players), leading to high school players spending a greater portion of each game on the field;
• The impact magnitudes sustained the high school players in the study sustained were nearly identical to the mean values reported in 3 previous studies of high school and college athletes, with game sessions resulting in significantly higher mean linear acceleration, rotational acceleration, and HITsp values;
• When evaluated by session type, game sessions resulted in significantly higher mean linear acceleration, rotational acceleration, and HITsp values compared with both contact and noncontact sessions, and mean rotational acceleration and HITsp values were significantly higher as well in contact practices as compared with noncontact practices;
• The HITsp value for the top 5% of all impacts of 30.5 was similar to that found at the collegiate level (32.0).
• Reducing the number of contact practices per week from 2 to 1 during the regular and postseason would decrease mean impact exposure by about 18% from 774 to approximately 736 impacts per season, with the impact reduction varying among players based on their position, and likely based on the team’s style of play;
• Eliminating all contact practices during the regular season and postseason, a drastic approach which could not occur without fundamental changes to the game, would result in a mean 39% decrease of head impacts (from 774 to 473, or approximately 31 impacts per week);  
• Unexpectedly, the magnitude among the top 1% and 0.5% of impacts during contact practices, while higher than those recorded for supposedly non-contact practices, was not statistically different.  While not without precedent (a previous study had reported linear accelerations during helmet-only practices slightly higher than during games), the researchers said the reason for why such supposedly “easier” sessions resulted in higher magnitude head impacts was “elusive,” although they speculated that it might be because head acceleration values have been shown to be lower when impact is anticipated, so that because “head impacts may not always be expected during non-contact practices, higher acceleration values may have resulted. Regardless of the explanation, exchanging contact practices for noncontact practices would be expected to reduce the total number of head impacts that athletes sustain; however, this may be at the expense of more impacts at higher magnitude.”  

Repetitive subconcussive impacts: effects still unknown

The Michigan study points to recent research suggesting that the number of head impacts sustained may play a more important role in putting an athlete at risk of developing CTE than clinically evident concussions.  Among them are studies of athletes in football (2-5) and ice hockey (4) found to have subtle changes in cerebral function in the absence of concussion symptoms or clinically measurable cognitive impairment which researchers linked to the volume of head impacts, and a much publicized case-study autopsy of a collegiate football player, Owen Thomas, with no reported history of concussions, which revealed early signs of CTE. (11)

“If verified,” Broglio writes, these reports “would support the use of head impact numbers to limit the head trauma volume experienced by an athlete each season.”

But, while recognizing that “contact sport athletes appear to be at a greater risk for developing CTE,”  he was careful to note the absence of studies “indicating the relationship between head impacts, concussions, and other factors (eg. genetic profile) that may trigger the disease pathway.”  Until the risk factors for developing CTE are better defined, Broglio says, the effect of reducing impacts by 18% to 40% in the risk for CTE is “unknown” and strategies designed to reduce those risks will necessarily remain “an educated guess, at best.”

“Ultimately, a comprehensive approach that includes, but is not necessarily limited to, modifications of head impact exposure, equipment modifications, rule changes and enforcement, and changes in game culture may all be needed to reduce injury risk,” Broglio concludes.  

1. Broglio SP, Martini D, Kasper L, Eckner JT, Kutcher JS.  Estimation of Head Impact Exposure in High School Football: Implications for Regulating Contact Practices.  Am J Sports Med 2013;20(10). DOI:10.1177/036354651302458 (epub September 3, 2013).
2. Breedlove EL, Robinson M, Talavage TM, et al. Biomechanical correlates of symptomatic and asymptomatic neurophysiological impairment in high school football. J Biomech. 2012;45(7):1265-1272.
3. Talavage TM, Nauman E, Breedlove EL, et al. Functionally-detected cognitive impairment in high school football players without clinically diagnosed concussion. J Neurotrauma. 2013;doi:10.1089/neu.2010.1512 (e-publ April 11, 2013)
4. Bazarian JJ, Zhu T, Blyth B, Borrino A, Zhong J.  Subject-specific changes in brain white matter in diffusion tensor imaging after sports-related concussion.  Magnetic Resources Imaging. 2012; 30(2): 171-180.
5. March N, Bazarian JJ, Puvenna V, Janigro M, Ghosh C, et. al. Consequences of Repeated Blood-Brain Barrier Disruption in Football Players. PLoS ONE 2013;8(3): e56805. doi: 10.1371/journal.pone.0056805.
6. Lipton M, Kim N, Zimmerman M, Kim M, Stewart W, Branch C, Lipton R. Soccer Heading Is Associated with White Matter Microstructural and Cognitive Abnormalities.  Radiology 2013;DOI:10.1148/radiol.13130545.
7. Benson B, McIntosh A, Maddocks D, et. al. What are the most effective risk-reduction strategies in sport concussion? Br J Sports Med 2013;47:321-326.
8. Alan Schwarz, “Teaching Young Players A Safer Way To Tackle.” New York Times, December 25, 2010 (http://www.nytimes.com/2010/12/26/sports/football/26tackling.html?pagewanted=all&_r=0)
9. Kontos P, Fazio V, Burkart S, Swindell H, Marron J, Collins M. Incidence of Sport-Related Concussion among Youth Football Players Aged 8-12 Years. J Pediatrics 2013. DOI 10.1016/j.jpeds.2013.04.011
10. Cobb BR, Urban JE, Davenport EM, Rowson S, Duma SM, Maldjian JA, Whitlow CT, Powers AK, Stizel JD. Head Impact Exposure in Youth Football: Elementary School Ages 9-12 Years and the Effect of Practice Structure. Ann Biomed Eng ( 2013): DOI: 10.1007/s10439-013-0867-6 (online ahead of print)
11. McKee AC, Stein TD, Nowinski CJ, et al. The spectrum of disease in chronic traumatic encephalopathy. Brain. 2013;136(Pt 1):43-

Posted September 6, 2013; revised September 9, 2013 to include Coach Bobby Hosea’s comments.