Head Impact Biomechanics in Youth Flag Football: A Prospective Cohort Study

Background: Youth flag football participation has rapidly grown and is a potentially safer alternative to tackle football. However, limited research has quantitatively assessed youth flag football head impact biomechanics. Purpose: To describe head impact biomechanics outcomes in youth flag football and explore factors associated with head impact magnitudes. Study Design: Cross-sectional study; Level of evidence, 3. Methods: We monitored 52 player-seasons among 48 male flag football players (mean ± SD; age, 9.4 ± 1.1 years; height, 138.6 ± 9.5 cm; mass, 34.7 ± 9.2 kg) across 3 seasons using head impact sensors during practices and games. Sensors recorded head impact frequencies, peak linear ( g) and rotational (rad/s2) acceleration, and estimated impact location. Impact rates (IRs) were calculated as 1 impact per 10 player-exposures; IR ratios (IRRs) were used to compare season, event type, and age group IRs; and 95% CIs were calculated for IRs and IRRs. Weekly and seasonal cumulative head impact frequencies and magnitudes were calculated. Mixed-model regression models examined the association between player characteristics, event type, and seasons and peak linear and rotational accelerations. Results: A total of 429 head impacts from 604 exposures occurred across the study period (IR, 7.10; 95% CI, 4.81-10.50). Weekly and seasonal cumulative median head impact frequencies were 1.00 (range, 0-2.63) and 7.50 (range, 0-21.00), respectively. The most frequent estimated head impact locations were the skull base (n = 96; 22.4%), top of the head (n = 74; 17.2%), and back of the head (n = 66; 15.4%). The combined event type IRs differed among the 3 seasons (IRR range, 1.45-2.68). Games produced greater IRs (IRR, 1.24; 95% CI, 1.01-1.53) and peak linear acceleration (mean difference, 5.69 g; P = .008) than did practices. Older players demonstrated greater combined event–type IRs (IRR, 1.46; 95% CI, 1.12-1.90) and increased head impact magnitudes than did younger players, with every 1-year age increase associated with a 3.78 g and 602.81-rad/s2 increase in peak linear and rotational acceleration magnitude, respectively ( P≤ .005). Conclusion: Head IRs and magnitudes varied across seasons, thus highlighting multiple season and cohort data are valuable when providing estimates. Head IRs were relatively low across seasons, while linear and rotational acceleration magnitudes were relatively high.

Analysis of Head Impact Biomechanics in Youth Female Soccer Players Following the Get aHEAD Safely in Soccer™ Heading Intervention

The effects of repetitive head impacts associated with soccer heading, especially in the youth population, are unknown. The purpose of this study was to examine balance, neurocognitive function, and head impact biomechanics after an acute bout of heading before and after the Get aHEAD Safely in Soccer™ program intervention. Twelve youth female soccer players wore a Triax SIM-G head impact sensor during two bouts of heading, using a lightweight soccer ball, one before and one after completion of the Get aHEAD Safely in Soccer™ program intervention. Participants completed balance (BESS and SWAY) and neurocognitive function (ImPACT) tests at baseline and after each bout of heading. There were no significant changes in head impact biomechanics, BESS, or ImPACT scores pre- to post-season. Deficits in three of the five SWAY positions were observed from baseline to post-season. Although we expected to see beneficial changes in head impact biomechanics following the intervention, the coaches and researchers observed an improvement in heading technique/form. Lightweight soccer balls would be a beneficial addition to header drills during training as they are safe and help build confidence in youth soccer players.

THE EFFECT OF A BODY CHECKING RULE CHANGE ON HEAD IMPACT BIOMECHANICS IN BANTAM ICE HOCKEY ATHLETES

Background: Body checking is the most common injury mechanism in ice hockey. Rule changes have sought to mitigate body checking exposure among youth players. In 2011, USA Hockey changed the legal body checking age from Pee Wee (11/12-year-olds) to Bantam (13/14-year-olds). Interestingly, Bantam players with checking experience during Pee Wee had a lower concussion risk relative to Bantam players without checking experience in a sample of Canadian youth hockey players. Understanding the head impact biomechanics underlying these findings could further elucidate the consequences of this rule change. Purpose: To determine the association between Pee Wee checking exposure and head impact biomechanics in a cohort of Bantam players. Methods: We prospectively collected data on Bantam ice hockey players during the 2006/07-2009/10 seasons and the 2012-2013 season. The 2006/07-2009/10 cohort (n= 61, age=13.9±0.5 years, height=168.2±8.7 cm, mass=59.9±10.4 kg) was allowed to body check (BC) as a Pee Wee player. The 2012-2013 cohort (n=15, age=13.3±0.4 years, height=167.5±7.4 cm, mass=57.5±8.6 kg) was not permitted to body check (NBC) as a Pee Wee player. Over the course of each season, head impacts were measured using in-helmet accelerometers. Only head impacts with linear acceleration ≥10 g were included in our analysis. Main outcome measures were mean linear acceleration (g) and rotational acceleration (rad/s2). Levene’s tests assessed equality of variance between groups. We employed mixed effects models to assess group differences in mean linear and rotational acceleration between BC and NBC groups. Results: The BC and NBC groups did not differ in height (t74=0.28, p=0.78) or mass (t74=0.84, p=0.40). When assessing group differences in head impact biomechanics, the NBC experienced significantly greater linear acceleration (F1,74=4.36, p=0.04) and greater rotational acceleration (F1,74=21.2, p<0.001) relative to the BC group. On average, the NBC group experienced 23.1 ± 0.87 g linear acceleration and 1993.5 ± 68.4 rad/s2 rotational acceleration compared to the BC group, which experienced 21.2 ± 0.30 g linear acceleration and 1615.9 ± 45.2 rad/s2 rotational acceleration. Conclusions: Bantam ice hockey players without body checking experience during their Pee Wee years experienced greater average linear and rotational acceleration relative to players with Pee Wee body checking experience. While removing body checking from Pee Wee ice hockey may reduce short-term injury risk, these athletes may demonstrate more high-risk head impact biomechanics when legally allowed to body check. Future research should continue to examine the influence of policy changes on head impact biomechanics and injury risk in youth ice hockey. [Figure: see text]

COMPARISON OF HEAD IMPACT BIOMECHANICS BETWEEN TACKLE AND FLAG YOUTH FOOTBALL

Background: There is growing fear among healthcare professionals and parents regarding youth tackle football, likely due to highly publicized concerns about potential long-term physical and cognitive health of professional football players. Parents and advocacy groups are pushing for state legislation to ban youth tackle football in favor of flag football to avoid repetitive head impacts that are potentially associated with late-life cognitive deficits. Although the head impact burden experienced during flag football is likely lower than tackle, no research has compared head impact exposure between youth tackle and flag football. Therefore, our purpose was to examine head impact exposure and magnitudes between youth tackle and flag football players. Methods: Twenty-seven tackle (age=11.0±1.5y, height=145.8±11.9 cm, mass=45.0±14.9 kg) and 29 flag football players (age=8.6±1.1y, height=133.9±8.4 cm, mass=33.9±9.5 kg) were enrolled in this prospective cohort study. Participants were fitted with head impact sensors (Triax Sim-G) worn throughout the entire 2017 season that recorded impact frequency and magnitude (linear [g] and rotational acceleration [rad/s2]). Athlete exposure was defined as one player participating in one session. Impact rates (IR) were calculated as impacts per one athlete exposure. Game, practice, and combined IR were compared between groups using impact rate ratios (IRR). IRR with 95% confidence intervals (CI) not containing 1.0 were considered statistically significant. Acceleration values were binned into low- and high-magnitude categories (linear split at 40 g, rotational split at 4,600rad/s2). Magnitude category frequencies were compared between groups using Chi-square test of association (p<0.05), and 90th percentile acceleration values are presented. Results: One-thousand nine-hundred and eight tackle (735 game, 1173 practice; 70.66 impacts/player) and 169 flag (101 game, 68 practice; 5.83 impacts/player) football head impacts were recorded. Tackle players experienced a higher impact rate during games versus practices (IRR=1.41; 95%CI:1.29 -1.55) while flag players experienced a lower impact rate (IRR=0.60; 95%CI:0.44-0.81). Practice and game head impacts combined resulted in tackle players (IR=3.06) accruing 4.61 times the impact rate (95%CI:3.94-5.40) of flag players (IR=0.66). Tackle players sustained a significantly greater head impact rate than flag players during games (tackle IR=3.83, flag IR=0.55; IRR=6.90; 95%CI:5.60-8.49) and practices (tackle IR=2.72, flag IR=0.93; IRR=2.91; 95%CI:2.28-3.72). Tackle 90th percentile linear acceleration was 53.32 g (median=32.50 g) and flag was 53.32 g (median=32.65 g). Tackle 90th percentile rotational acceleration was 7,000 rad/s2 (median=3,200rad/s2) while flag was 8,300 rad/s2 (median=4,100rad/s2). Tackle experienced a significantly higher frequency of low-magnitude rotational acceleration impacts (71.6% vs. 57.4%) and lower frequency of high-magnitude impacts than flag (28.4% vs 42.6%;?2=15.15, p<0.001). There were no significant associations for linear acceleration (p=0.75). Conclusions/Significance: Our results indicate youth flag football head impact rates are 82%-88% lower compared to tackle. Contrary to general belief, youth flag football players experienced numerous head impacts with a greater tendency for high-magnitude rotational acceleration head impacts. Although fewer head impacts occur during youth flag football, parents and coaches should be aware that head impacts do occur during practices and games. Whether high-magnitude or high-frequency head impacts influence long-term health remains unknown. Our findings provide novel evidence into the head impact exposure occurring during youth tackle and flag football. Longitudinal studies examining head impact biomechanics and advanced neuroimaging in youth tackle and flag football players nationwide is warranted to ensure long term cognitive health.