This paper analyzes data on the dynamic response of the living human head and neck to -Gx impact acceleration. The Calspan “3D Computer Simulator of a Motor Vehicle Crash Victim,” Ultrasystems “Crash Victim Simulator - Light Aircraft” and Boeing Computer Services “Prometheus” were used to provide estimates of the responses monitored. Inputs to the programs were made as comparable as program restrictions would allow. Outputs were compared to each other as well as to the corresponding human test run. Program outputs proved to be consistent but failed to adequately replicate human results. Inclusion of head to neck articulation did not by itself improve results. Relocation of the head pivot away from the occipital condyles or introduction of muscular activity was indicated.