Magnitude and frequency of head impact among university American football players

Abstract

The purpose of this study was to analyze head impact kinematics at different locations of Japanese university American football players using a 6DOF (degrees of freedom) device. The subjects of this study were 43 players who belonged to T University in the Kanto Collegiate American Football Association second division. We used a Vector Mouthguard (i1 Biometrics Inc.) equipped with a 6DOF to measure the head LA (linear acceleration), AA (angular acceleration) and AV (angular velocity), as well as the number of head impacts during collisions, and evaluated 4 impact locations (front, side, back, and top) in detail. The total number of head impacts was 2,070 during games and 10,007 during practice sessions for a total of 7 games and 41 practices during fall regular seasons over a 2-year period. The most common head impact location was the front (43.5%), followed by the side (41.9%), top (10.9%), and back (3.7%). When classifying the total number of head impacts at these locations according to player position, skill players showed the highest proportion of side impacts (p < 0.05), whereas linemen showed the highest proportion of frontal impacts (p < 0.05) compared to the other locations. These results support previous studies conducted for university American football players in the United States. That is, the frequency and location of head impacts is greatly influenced by player position. Regarding the magnitude of head impact locations, the LA and AA values for back of the head impacts were the highest both at games and practice sessions. In addition, the AA value for impacts to the top of the head was much higher than the AA value for impacts to the front and side (p < 0.05). Also, there were significant positive correlations between peak LA and peak AA at all head impact locations for games and practice sessions based on player position (p < 0.05). Skill players showed significant positive correlations between peak AA and peak AV at all head impact locations in games (p < 0.05). In comparison, linemen showed significant positive correlations between peak AA and peak AV for frontal and side impacts for games and frontal, side, and top of head impacts in practice sessions (p < 0.05). As a result, it was clear that Japanese university American football players could not stabilize the head during collisions. In conclusion, it was found that the frequency of head impact locations in Japanese university American football players was the same as that in the USA. In head impact kinematics during collisions, Japanese university American football players showed different characteristics from their American counterparts. In the future, we should take into account neck muscular strength and motion analysis to better understand the influence of head impacts on Japanese university American football players.

Head Rotational Kinematics, Tissue Deformations, and Their Relationships to the Acute Traumatic Axonal Injury

“…In order to quantify the possible relationships between the head angular kinematics and the axonal/brain tissue deformations beyond the experimental loadings studied herein, a series of 104 simulations per direction were performed for axial and sagittal rotations for a wide range of angular loading conditions with different values of peak angular velocity and peak angular acceleration varied from 25–400 rad/s and 25–250 krad/s 2 , respectively. This range was selected to cover the current and previous pig TBI experiments performed in our laboratory [ 14 – 16 , 19 ], sport- or fall-related human head impact kinematics measured on-field [ 6 , 7 , 9 ] or reconstructed in laboratory [ 8 , 10 – 13 ], and primate TBI experiments that were previously performed for severe diffuse axonal injury [ 1 ], all mass scaled to pig. For these parametric simulations, idealized full cycle sinusoidal angular acceleration signals were used as the loading traces.…”

“…These relationships should be explored over a wide range of loading conditions and at different rotational directions to provide a generalized understanding of how the characteristic of head kinematics affects the axonal fiber and brain tissue deformation and deformation-rate responses. Such an investigation is important because head kinematic parameters of different sports such as soccer, American football, hockey, boxing, rugby, Australian football, and accidental events such as fall have demonstrated different characteristics in terms of magnitude and duration of brain motions within the skull [ 1 , 6 – 13 ]. For examples, as shown in Fig.…”

“…For examples, as shown in Fig. 1 , some accidental events such as standing fall, falls to ice in hockey, and unhelmeted head-to-head impacts in boxing produce high kinematic values in short duration while helmeted head impacts in football or head to padded shoulder/elbow impacts in hockey produces lower peak magnitude and longer duration [ 6 – 13 ]. Also, some studies have shown brain vulnerabilities to be dependent on head rotational direction [ 14 – 16 ].…”

“… Examples of sport- or fall-related human head impact kinematics measured on-field [ 6 , 7 , 9 ] or reconstructed in laboratory [ 8 , 10 – 13 ] and primate TBI experiments that were previously performed for severe diffuse axonal injury [ 1 ] in ( a ) human scale and ( b ) all mass scaled to pig …”