Less contact during practice could mean a lot less exposure to head injuries among young football players and the kind of repetitive subconcussive blows [1] that some researchers suggest can lead to long-term brain injury, but does not result in exposure to higher impact hits during games, says a new study. [1]
Researchers at Wake Forest Baptist Medical Center and Virginia Tech measured the number, force, location, and effect of blows to the head in 50 youth-league players ages 9 to 12. Their study followed a 2012 study [2] [2] of small group of youth players, ages 7 to 8, in which they found that most high impact hits occurred during practice, not games. That study prompted Pop Warner to swiftly move to impose limits [3][3] on the time spent in full-contact practice.
The new study involved one team that, while not affiliated with Pop Warner, chose to follow its new practice rules, and two others that did not. Significantly, the data showed that reducing the number of head hits in practice did not, as a later study [4] by researchers at the University of Pittsburgh Medical Center [4] predicted, lead to higher force impacts during games.
This is precisely as the researchers in their earlier study had hoped. Their finding suggests that the heavy criticism of the Pop Warner practice limits by the UPMC researchers [5] that the new rules would "not only have little effect on reducing on reducing concussions but may also actually increase the incidence of concussions in games via reduced time learning proper tackling in practice" may have been wide of the mark.
"The concern is if we don't teach kids how to hit in practice, they're going to get blown away in the games," said Stefan Duma of the School of Biomedical Engineering and Sciences and one of the co-authors of the study, in an interview with The New York Times. "This shows you can dramatically cut the amount of exposure in practice and have no more exposure during the games."
Numerous concussion and biomechanical studies have been conducted involving high school and college football players, but only few studies have focused on players under the age of 14, who represent more than 70 percent of those playing the sport. As a result, there has been, up to now, no clear, scientifically-based understanding of the number, force, and effect of blows to the head in young players, said Steven Rowson, Ph.D., assistant professor at the Virginia Tech-Wake Forest University School of Biomedical Engineering and Sciences and lead author of the study, published online in the journal Annals of Biomedical Engineering.
To quantify youth football players' exposure to head impacts in practices and games over the course of a single season, the researchers outfitted helmets of 50 players on three teams in two different leagues with the HIT (Head Impact Telemetry) system, an array of helmet-mounted accelerometers (i.e. hit sensors) installed on an elastic base inside the helmet. Data from the sensors were transmitted wirelessly to a computer on the sideline and processed to measure both the linear and rotational head acceleration resulting from each impact. All the data were then analyzed for each individual player basis and averaged to represent the exposure level of a typical 9- to12-year-old football player.
The data yielded the following results:
Previous studies over the last decade have investigated the frequency and magnitude of head impacts in other tackle football populations, including youth (7-8 years),[2] high school (14-18 years),[5-8] and college (18-23 years). Data from these studies show a trend of increasing acceleration magnitude and impact frequency with increasing level of play.
Not surprisingly, the 9-12 year old players in the current study were found to experience linear acceleration magnitudes between those found in 7-8 year old players[2] and high school players, although, for rotational acceleration, the 95th percentile magnitude found in this study was less than that found previously in younger players.
Rotational acceleration tends to correlate well with linear acceleration, though impact location can heavily influence the relationship. Players in this study experienced more impacts to the front of their helmets and fewer to the side than the 7- to 8-year-old players who were the subject of a 2012 study [2] [2] by the same researchers.
In that study, impacts to the front of player's helmets were associated with lower rotational acceleration magnitudes, while those to the side were associated with higher magnitudes. As with magnitude, the impact frequency reported in the current study fell between those of 6- to 9-year-olds and high school athletes, with the average player experiencing 240 impacts over the course of a season compared to 107 impacts per season for 6- to 9-year-old players, and 565 for high school players.
This trend can be partially explained by the fact that the number of sessions (practices and games) increased as the level of play increased, with the younger players in the 2012 study involved in 9.4 practices and 4.7 games for a total of 14.1 sessions, while players in the current study participated in an average of 14.4 contact practices and 7.4 games, for a total of 21.8 sessions, but fewer practices and games, and fewer impacts per session, than high school players, who experienced on average 15.9 impacts per session compared to the 10.6 impacts per session experienced by the 9-12 year old players in the current study. The age-related differences reported among these three age groups are most likely due to increased size, athleticism, and aggression in older players, said Rowson.
Comparison of head impact exposure across various level of play[2,5-7]
Linear acceleration | (g) | Rotational acceleration | (rad/s2) | ||
Level of Play |
Number of impacts per season |
Median (50%) |
95% |
Median (50%) |
95% |
Youth (7-8 years) | 107 | 15 | 40 | 672 | 2347 |
Youth (9-12 years) | 240 | 18 | 43 | 856 | 2034 |
High school (14-18 years) | 565 | 21 | 56 | 903 | 2527 |
College (19-23 years) | 1000 | 18 | 63 | 981 | 2975 |
Players experienced slightly greater impact frequencies and acceleration magnitudes in games than in practice, similar to findings of high school and college football studies. For example, a group of high school players, experienced a mean linear acceleration magnitude of 23 g in practices and 25 g in games while the players in this study had a mean linear acceleration magnitude of 22 g in practices and 23 g in games.
With regard to impact frequency, players in this study experienced a similar number of impacts per practice as per game. The rate of impact in practice was similar to the 9.2 impacts per practice that were reported for high school football players. However, the high school players sustained 24.5 impacts per game. These data suggest that high school players experience fewer impacts in practice than in games, while the 9-12 year old players in this study had roughly equal numbers of impacts per session for the two session types.
The players on team A who adopted the new Pop Warner rule[3] changes - which now permit no more than a third of practice time, and no more than 40 minutes per session to contact drills and require coaches to give each player a certain minimum amount of playing time - absorbed an average of 37 percent to 46 percent fewer hits than players on teams B and C during practices and games over the course of season.
In addition to the Pop Warner rules, the authors attributed the reduction in impacts to several other factors:
"The data collected in this study may have applications towards improving the safety of youth football through rule changes, coach training, and equipment design. Prior to the 2012 season, many youth football organizations, including the league in which team A competed, modified rules, and provided coaches with practice guidelines to reduce head impacts in practice," Rowson noted.
"The data collected in this study suggest that total head impact exposure over the course of a season can be reduced significantly by limiting contact in practices to levels below those experienced in games. In addition to guiding future rules for youth football, this study can be used to aid designers in developing youth-specific football helmets that may be able to better reduce head accelerations due to head impacts for young football players. Impact location, frequency, and head acceleration magnitudes can be used to optimize helmet padding to maximize protection while keeping factors such as helmet size and mass to age appropriate levels."
The vast majority of head impacts recorded in both games and practices were below acceleration magnitudes generally associated with concussions; though, some high magnitude impacts, similar to those seen among older players, did occur.
"It is striking that you can cut head impacts for a player in half just by modifying practice, and it does not seem to change the game," said Alexander Powers, M.D., assistant professor of neurosurgery at Wake Forest Baptist and co-author of the study. "This may be very important in kids where brains are developing."
"We hope that the findings will help improve the safety of youth football through rule changes to limit contact in practices, coach training and equipment design, especially in developing youth-specific helmets to better reduce accelerations from head impacts," Rowson said.Source: WakeHealth
1. 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)
2. Daniel R, Rowson S, Duma S. Head Impact Exposure in Youth Football. Ann. Biomed Eng 2012;40(4):976-981.
3. http://www.popwarner.com/About_Us/Pop_Warner_News/Rule_Changes_Regarding... [3] (accessed May 17, 2012)
4. 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
5. Broglio, S. P., T. Surma, and J. A. Ashton-Miller. High school and collegiate football athlete concussions: a biomechanical
review. Ann. Biomed. Eng. 2012;40(1):37-46.
6. Rowson, S., and S. M. Duma. Development of the star evaluation system for football helmets: integrating player
head impact exposure and risk of concussion. Ann. Biomed. Eng. 2011;39(8):2130-2140.
7. Rowson, S., S. M. Duma, J. G. Beckwith, J. J. Chu, R. M. Greenwald, J. J. Crisco, P. G. Brolinson, A. C. Duhaime,
T. W. McAllister, and A. C. Maerlender. Rotational head kinematics in football impacts: an injury risk function for
concussion. Ann. Biomed. Eng. 2012;40(1):1-13.
Posted August 15, 2013
Links:
[1] https://www.momsteam.com/node/4492
[2] https://www.momsteam.com/node/4671
[3] http://www.popwarner.com/About_Us/Pop_Warner_News/Rule_Changes_Regarding_Practice___Concussion_Prevention_s1_p3977.htm
[4] https://www.momsteam.com/node/6182
[5] https://www.momsteam.com/health-safety/youth-football-concussion-study-generates-controversy-over-suggestion-that-limiting-contact-practices-mistake
[6] https://www.momsteam.com/head-impact-exposure-in-youth-football-surprisingly-high-limits-in-contact-practices-urged
[7] https://www.momsteam.com/health-safety/seven-ways-to-reduce-risk-of-brain-trauma-in-contact-and-collision-sports