Head impact exposure in collegiate football players

Abstract

In American football, impacts to the helmet and the resulting head accelerations are the primary cause of concussion injury and potentially chronic brain injury. The purpose of this study was to quantify exposures to impacts to the head (frequency, location and magnitude) for individual collegiate football players and to investigate differences in head impact exposure by player position. A total of 314 players were enrolled at three institutions and 286,636 head impacts were recorded over three seasons. The 95th percentile peak linear and rotational acceleration and HITsp (a composite severity measure) were 62.7g, 4378rad/s(2) and 32.6, respectively. These exposure measures as well as the frequency of impacts varied significantly by player position and by helmet impact location. Running backs (RB) and quarter backs (QB) received the greatest magnitude head impacts, while defensive line (DL), offensive line (OL) and line backers (LB) received the most frequent head impacts (more than twice as many than any other position). Impacts to the top of the helmet had the lowest peak rotational acceleration (2387rad/s(2)), but the greatest peak linear acceleration (72.4g), and were the least frequent of all locations (13.7%) among all positions. OL and QB had the highest (49.2%) and the lowest (23.7%) frequency, respectively, of front impacts. QB received the greatest magnitude (70.8g and 5428rad/s(2)) and the most frequent (44% and 38.9%) impacts to the back of the helmet. This study quantified head impact exposure in collegiate football, providing data that is critical to advancing the understanding of the biomechanics of concussive injuries and sub-concussive head impacts.

Figure 1

Study wide peak linear acceleration (g), peak rotational acceleration (rad/s²) and HITsp distributions of head impacts. Data are a percentage of all impacts for individual players with median [25–75%] values plotted at each bin in the distribution.

Figure 2

After categorizing by player position, the median [25% – 75%] frequency of head impacts per practice and head impacts per game were linearly correlated with the median [25% – 75%] frequency of head impacts per season (slope = 0.02, R² = 0.934 and slope = 0.04, R² = 0.929, respectively). The vertical dotted lines identify the positions associate with each median value.

Figure 3

The median [25%– 75%] of the 95^th percentile of peak linear acceleration (g) as a function of the median [25%– 75%] number of head impacts per season and categorized by player position. Analogous values for peak rotational acceleration (rad/s²) and HITsp are provided in Table 1.

Figure 4

The median [25%– 75%] of the 95^th percentile of peak linear acceleration (g) as a function of the median [25%– 75%] frequency of impacts at each helmet location and categorized by player position. Analogous values for peak rotational acceleration (rad/s²) are provided in Table 2.