Concussions in Boxers: Head Rotations and Neck Stiffness

Background: The human head-and-neck has three degrees of rotational freedom – pitch, roll, and yaw. While the evolution of the head-and-neck mobility may have increased the overall fitness of homo sapiens, our head-and-neck mobility may have also introduced some differential vulnerability to injuries in impact-induced head rotations about the pitch, roll, and yaw axes. Methods and Findings: We examined impact-induced head rotations in boxing matches by analyzing videos. Our objective was to seek a quantitative relationship between impact-induced head kinematics and the knockout outcome. For each of the three rotational degrees of freedom, head angular velocities of impact-induced head rotations were significantly higher in knockout hits than in control hits without a knockout (p < 0.02). Knockout thresholds in pitch-roll-yaw measured as impact-induced head angular velocities were anisotropic with the lowest threshold in roll and became progressively higher in yaw and pitch, in that order. Regardless of the pitch-roll-yaw bearing, the velocities of the striking fists in knockout hits were not significantly higher than those in control hits. Conclusions: Accurate prediction of knockout via head kinematics was possible with pitch-roll-yaw information. Impact-induced head kinematics was strongly influenced by neck stiffness, making a case for the utility of reflexively increasing neck stiffness as an effective way to reduce impact-induced head rotations and concussion risk.