Factors Affecting Head Impact Exposure in College Football Practices: A Multi-Institutional Study.

Biomechanical data collected from head impacts in football have been used to characterize exposure and predict injury risk. This study sought to specifically quantify the factors that contribute towards player head impact exposure in college football practices. All players included in this study were outfitted with football helmets instrumented with accelerometer arrays (Head Impact Telemetry System). Head impact exposure was defined by the number of head impacts each player experienced in practice, the number of practice head impacts normalized by the number of practice sessions (practice head impact rate), and the 95th percentile linear and rotational resultant head impact accelerations. Practice head impact rate was observed to vary significantly with player position (p < 0.0001; η2 = 0.46), team (p = 0.0016; η2 = 0.03), and the number of game impacts (p < 0.0001; η2 = 0.03), which served as a correlate for player ability. Even after controlling for practice participation, player position, team, and ability, differences between individuals accounted for 48% of the variance in head impact exposure in practice. This work demonstrates the importance of considering head impact exposure on a subject-specific basis rather than estimating head impact exposure from aggregate data.