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This paper describes the efforts of one group to improve the biomechanical fidelity of ATD headforms used in automotive crash testing. On the basis of recent cadaver head impact studies and on the literature dealing with facial bone tolerances, several refinements have been made to the Hybrid III head-form. These include a slight modification of effective skull stiffness, the addition of a frangible faceform sub-assembly and the introduction of a compliant mandible. The purpose of these modifications is to improve both the response characteristics to impact as well as to provide a direct means to monitor for facial bone injury.

Recently, several cases of mild traumatic brain injury to American professional football players have been reconstructed using instrumented Hybrid III anthropomorphic test dummies ATDs. The translational and rotational acceleration responses of injured and uninjured players'' heads have been documented. The acceleration data have been processed according to all current head injury assessment functions including the GSI, HIC and GAMBIT among others. A new hypothesis is propounded that the threshold for head injury will be exceeded if the rate of change of kinetic energy of the head exceeds some limiting value. A functional relation is proposed, which includes all six degrees of motion and directional sensitivity characteristics, relating the rate of change of kinetic energy to the probability of head injury. The maximum value that the function achieves during impact is the maximum power input to the head and serves as an index by which the probability of head injury can be assessed.