Statement of purpose Estimate rates of sport-related concussion (SRC) in high school football and evaluate a rule change over 5 seasons.
Methods/Approach The Michigan High School Athletic Association (MHSAA) surveillance system records total numbers of participating athletes and circumstances of each SRC occurring in athletic- sanctioned events. Across five seasons, MHSAA progressively limited time for collision practices. We estimated player-days exposed as the total number of players multiplied by the total number of possible practices (11 weeks, 4 days each) or competitions (9 weeks, 1 day each) each regular season. Rate ratios (RR) and 95% confidence intervals (CI) compared practice and competition SRC, and compared each season relative to the most recent season (2019/20). Annual SRC rates modeled by year (2015/16–2018/19, 2019/20) and event (practice, competition) using Poisson regression estimated rate difference-in-differences and 95% CI.
Results The overall football SRC rate was 0.82/1,000 player-days. The greatest proportion of practice SRC occurred during the first two weeks of the season (preseason;40.6%) and competition SRC occurred between weeks 5–9 (63.5%). The competition SRC rate (3.10/1,000 player-days) was higher than practice (0.35/1,000 player-days; RR:8.87, 95%CI:8.47,9.29). For practice SRCs, risk of SRC was lower in 2019/20 than 2015/16 (RR:0.85, 95%CI:0.75,0.97) and 2016/17(RR:0.84, 95%CI:0.74,0.95). The competition rate was lower in 2019–20 than 2015–16 (RR:0.90, 95%CI:0.82,0.98). However, the difference-in-differences analysis for practice vs. competition in the 2019/20 season vs. the 2015/16- 2018/19 seasons was null (-0.015, p=.958).
Conclusions SRC rates in football were higher in competition than practice. The reduction noted in practice SRC in 2019/20 compared to prior seasons was not greater than the reduction observed during competition.
Significance Highlighting when SRC occur throughout an athletic season may focus preventative efforts. The strategy of progressively limiting collision practices did not alone reduce SRC in Michigan high school football.
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