This report reviews research, conducted prior to 2004, in four areas of neck biomechanics that pertain to head-supported mass (HSM). First, computer models of the head and neck are reviewed for their biofidelity and versatility. Second, neck injury criteria are reviewed for their applicability to studying HSM-related neck injuries. Third, existing studies of HSM effects on head-neck response to impact are reviewed. Fourth, a review of muscle activation and its effects on neck impact response is presented. This study found that HSM poses an undermined risk to the safety of the Soldier. Computational simulations exist to accurately simulate human response to a variety of loading conditions, including simulations of live occupant response with passive or active muscles. Neck injury criteria can be used to determine the susceptibility of the simulated occupant to potential neck injury. Further studies utilizing these tools will ensure that military personal are not subjected to unnecessary safety risks as a consequence of additional head-supported mass.