Physical properties of the human head: mass, center of gravity and moment of inertia.

This paper presents a synthesis of biomedical investigations of the human head with specific reference to certain aspects of physical properties and development of anthropometry data, leading to the advancement of dummies used in crashworthiness research. As a significant majority of the studies have been summarized as reports, an effort has been made to chronologically review the literature with the above objectives. The first part is devoted to early studies wherein the mass, center of gravity (CG), and moment of inertia (MOI) properties are obtained from human cadaver experiments. Unembalmed and preserved whole-body and isolated head and head-neck experiments are discussed. Acknowledging that the current version of the Hybrid III dummy is the most widely used anthropomorphic test device in motor vehicle crashworthiness research for frontal impact applications for over 30 years, bases for the mass and MOI-related data used in the dummy are discussed. Since the development and federalization of the dummy in the United States, description of methods used to arrive at these properties form a part of the manuscript. Studies subsequent to the development of this dummy including those from the US Military are also discussed. As the head and neck are coupled in any impact, and increasing improvements in technology such as advanced airbags, and pre-tensioners and load limiters in manual seatbelts affect the kinetics of the head-neck complex, the manuscript underscores the need to pursue studies to precisely determine all the physical properties of the head. Because the most critical parameters (locations of CG and occipital condyles (OC), mass, and MOI) have not been determined on a specimen-by-specimen basis in any single study, it is important to gather these data in future experiments. These critical data will be of value for improving occupant safety, designing advanced restraint systems, developing second generation dummies, and assessing the injury mitigating characteristics of modern vehicle components in all impact modalities.