Investigating the influence of head kinematics on head injury metrics and factors to consider for football helmet design

There is a need to understand the relationship between head kinematics, impact severity metrics, and overall helmet performance as sports-related concussions continue to be prevalent. This study evaluates these relationships, emphasizing newly developed severity metrics that consider both translational and rotational contributions. Impact tests were performed following the NFL testing protocol on four prominent football helmets. The resulting data was used to determine Head Acceleration Response Metric (HARM), Diffuse Axonal Multi-Axis General Evaluation (DAMAGE), and Head Injury Criterion (HIC). HARM scores, a combination of HIC and DAMAGE, were ultimately used to solve for a Helmet Performance Score. When analyzing all impacts, DAMAGE showed a stronger correlation to HARM than HIC ( R2 = 0.76 vs R2 = 0.57); however, the strongest correlation existed between peak resultant angular velocity (PRAV) and HARM ( R2 = 0.87). When examining impacts at only the side, side upper (SU), and oblique front (OF) locations grouped together, HIC demonstrated the strongest correlation to HARM in the study ( R2 = 0.96). PRAV was the best predictor for HARM over peak resultant linear acceleration (PRLA) and peak resultant angular acceleration for four of the six impact locations (C, D, FMCO, and FMS) when analyzing the sites individually. The remaining locations (SU and OF) best predicted HARM using PRLA. These results are presented and discussed to aid in the research, design, and development of football helmets.