Abstract
Repetitive head impact exposure sustained by athletes of contact sports has been hypothesized to be a mechanism for concussion and a possible explanation for the high degree of variability in sport-related concussion biomechanics. In an attempt to limit repetitive head impact exposure during the football preseason, the NCAA eliminated two-a-day practices in 2017, while maintaining the total number of team practice sessions. The objective of this study was to quantify head impact exposure during the preseason and regular season in Division I college football athletes to determine whether the 2017 NCAA ruling decreased head impact exposure. 342 unique athletes from five NCAA Division I Football Bowl Subdivision (FBS) programs were consented and enrolled. Head impacts were recorded using the Head Impact Telemetry (HIT) System during the entire fall preseasons and regular seasons in 2016 and 2017. Despite the elimination of two-a-day practices, the number of preseason contact days increased in 2017, with an increase in average hourly impact exposure (i.e., contact intensity), resulting in a significant increase in total head impact burden (+ 26%) for the 2017 preseason. This finding would indicate that the 2017 NCAA ruling was not effective at reducing the head impact burden during the football preseason. Additionally, athletes sustained a significantly higher number of recorded head impacts per week (+ 40%) during the preseason than the regular season, implicating the preseason as a time of elevated repetitive head impact burden. With increased recognition of a possible association between repetitive head impact exposure and concussion, increased preseason exposure may predispose certain athletes to a higher risk of concussion during the preseason and regular season. Accordingly, efforts at reducing concussion incidence in contact sports should include a reduction in overall head impact exposure.
Highlights
Understanding the deleterious effects of repetitive subconcussive head impact exposure through routine participation in contact sports has come to the forefront of sport-related concussive injury prevention efforts
All five National Collegiate Athletic Association (NCAA) Division I Football Bowl Subdivision (FBS) programs participated in the study during the 2016 and 2017 seasons and had the same head coaches during both seasons
Two hundred twenty-five (225) athletes from five NCAA Division I football programs participated in contact activities over four preseason and thirteen regular season weeks during 2016, for a total of 10,861 athletedays
Summary
Understanding the deleterious effects of repetitive subconcussive head impact exposure through routine participation in contact sports has come to the forefront of sport-related concussive injury prevention efforts. In a study of National Collegiate Athletic Association (NCAA) Division I athletes that did not sustain concussion, McAllister et al identified significant correlations between head impact exposure metrics and post-season measures of white matter diffusivity in several brain regions.[26] These findings imply the presence of accumulating structural and physiological changes in the brain that are correlated to repetitive head impact exposure and occur without the diagnosis of concussion. Other studies identified post-season cognitive changes in non-concussed athletes with higher levels of head impact exposure throughout the season.[24,36] This points to a possible correlation between increasing levels of repetitive head impact exposure and the development of cognitive changes during a football season
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