Inconsistent results have been reported for helmeted impact responses between the two most commonly used headforms: The National Operating Committee on Standards for Athletic Equipment (NOCSAE) and the Hybrid III (HIII). There is a need to understand the reasons for the different responses of the headforms so that helmet protection may be discerned independent of the headform. In this study, the kinematic response and brain injury measures of the NOCSAE and HIII headforms at three impact orientations with three helmet models on an inclined anvil were compared. The results showed that the peak linear acceleration from the two headforms were within 6.3% on average for all impacts. However, despite the higher moment of inertia of the HIII headform, it did not have a consistently lower rotational acceleration compared to the NOCSAE headform. The differing headform rotational responses were primarily due to differences in the headforms’ center of gravity location. This led to differences in couples and accelerations, which tended to be most severe in frontal impact orientations. The variation in rotational responses of the headforms seems to be also dependent on the helmet type, with helmet A having greater variation compared to helmets B and C. Differences in the rotational kinematics of the two headforms led to a 47% average difference in their brain injury measures.

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