Head impacts during high school football: a biomechanical assessment

Abstract

Context: Little is known about the impact biomechanics sustained by players during interscholastic football.

Objective: To characterize the location and magnitude of impacts sustained by players during an interscholastic football season.

Design: Observational design.

Setting: On the field.

Patients or other participants: High school varsity football team (n = 35; age = 16.85 +/- 0.75 years, height = 183.49 +/- 5.31 cm, mass = 89.42 +/- 12.88 kg).

Main outcome measure(s): Biomechanical variables (linear acceleration, rotational acceleration, jerk, force, impulse, and impact duration) related to head impacts were categorized by session type, player position, and helmet impact location.

Results: Differences in grouping variables were found for each impact descriptor. Impacts occurred more frequently and with greater intensity during games. Linear acceleration was greatest in defensive linemen and offensive skill players and when the impact occurred at the top of the helmet. The largest rotational acceleration occurred in defensive linemen and with impacts to the front of the helmet. Impacts with the highest-magnitude jerk, force, and impulse and shortest duration occurred in the offensive skill, defensive line, offensive line, and defensive skill players, respectively. Top-of-the-helmet impacts yielded the greatest magnitude for the same variables.

Conclusions: We are the first to provide a biomechanical characterization of head impacts in an interscholastic football team across a season of play. The intensity of game play manifested with more frequent and intense impacts. The highest-magnitude variables were distributed across all player groups, but impacts to the top of the helmet yielded the highest values. These high school football athletes appeared to sustain greater accelerations after impact than their older counterparts did. How this finding relates to concussion occurrence has yet to be elucidated.

Keywords: Head Impact Telemetry System; acceleration; concussions; mild traumatic brain injuries.

Figures

Figure 1. The Head Impact Telemetry System encoder placed within the padding of a football helmet around the crown of the head. (Photograph courtesy of Simbex LLC, Lebanon, NH.)

Figure 2. Distribution of impact locations across the helmet. Impacts to the right and left sides were grouped together.

Figure 3. Representative impact curve. A number of variables were calculated from the impact data and participant demographics. Jerk  =  (Ba−Aa)/ΔB−A time. Force  =  Ba * head mass. Impulse  =  [Area under curve from Aa to Ca] * time. Impact duration  =  time from At to Ct. a indicates acceleration values; t, time values.

Figure 4. Mean number of impacts sustained during practices and games by player positions.

Figure 5. Resultant linear acceleration by player position and impact location.

Figure 6. Resultant rotational acceleration by player position and impact location.