Concussions are one of the most common injuries in sport and can result in detrimental long-term health effects. To reduce the severity of concussion and head injury, protective headgear has been implemented and is continually evaluated to minimize head kinematics after impact. For investigation of head dynamic behavior in impact and to conduct helmet certification testing, surrogate anthropomorphic test device head and neck models are used. Although there is evidence of head-neck-body coupling in impacts, most testing methods use isolated surrogate head-neck assemblies that ignore or provide no justification for the simulated torso mass on resultant head behavior in impacts. The objective of this thesis was to quantify the head kinematic and upper neck kinetic differences in head impacts using an isolated head-neck system fixed to a translating linear rail and a head-neck assembly fixed to a dummy torso. A secondary objective was to overview the repeatability of a novel surrogate neck model when fixed to a translating linear rail.

One Hybrid III neck and three copies of a novel surrogate neck (Phase III neck) were fixed to a Hybrid III headform fit with a NOCSAE certified football helmet and subjected to two sets of impacts;​ 1) fixed to a translating platform on a linear rail and, 2) fixed to a Hybrid III dummy torso. Direct head impacts were conducted with a pendulum impactor at 4.0 m/s to frontal, lateral, and front boss locations. The impact metrics investigated were head center of gravity linear acceleration, angular acceleration, angular velocity, and upper neck impact and peak force, and upper neck impact and peak moment.

The Phase III neck showed acceptable within-neck and between-neck repeatability based on the coefficient of variation of repeatability, coefficient of variation of reproducibility, and normalized absolute difference values. Normalized absolute difference values of >​20% between the surrogate necks and the Hybrid III neck and significantly different ANOVA results indicate the surrogate neck and the Hybrid III neck produce differing head kinematics during impact.

Significant differences were found in almost all impact metrics between the system with the head-neck assembly fixed to a translating linear rail (head-neck-rail system) and a head-neck assembly fixed to a Hybrid III dummy torso (head-neck-torso system). An independent samples, two-tailed t-test, a Welch t-test, or a Mann-Whitney U Test were used to analyze the seven impact metrics from impacts with four surrogate necks. Out of a combination of 28 impact metric comparisons, 75% (21 of 28), 71.4% (20 of 28), and 50% (14 of 28) of impact metrics were higher for the head-neck-torso system compared to the head-neck-rail system in frontal, lateral, and front boss impact locations, respectively. Linear acceleration was the only impact metric that was higher for the head-neck-torso system for all four surrogate necks in all three impact locations.

The results from this investigation suggest that torso mass influences the head center of gravity kinematics and the upper neck kinetics. However, it remains unknown which approach is the better approximation of human head dynamics from a head impact in sport, and further investigation is needed to determine which method is more appropriate for use in helmet testing to ensure the most accurate methods are used to increase player safety. Additionally, significant differences between the head kinematics and upper neck kinetics from the Hybrid III neck and the Phase III neck emphasizes the demand for the continued development and biofidelity assessment of surrogate neck models such as the Phase III neck to compare against the Hybrid III neck, to ultimately assist researchers in improving injury assessment effectiveness.