Concussions in Boxers: Head Rotations and Neck Stiffness

Abstract

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.