Kinematic response of the neck to voluntary and involuntary flexion

Methods: The dynamic head-neck responses of human subjects and cadavers undergoing involuntary impact loading conditions have been studied extensively in order to define the kinematics of the neck undergoing rapid movements, but little detailed information is available regarding slower, voluntary motions. In this study, the dynamic kinematics of head/neck complex during subject-controlled, or voluntary head motion have been investigated to compare with the kinematics to involuntary response. Five male human subjects experienced two-types of posterior/anterior neck flexion: flexion initiated under their own volition, and flexion in response to -15Gx acceleration of the torso. Tri-axial photo target mounts were placed on a custom-fit plate at the mouth, on the first thoracic vertebra, and on the sled. High speed movie cameras captured the photo target motion. Linear and angular displacement and velocity of the head and T1 and sled were computed using customized data- processing software. The neck kinematics were represented by a 2-pin linkage which connected the anatomical origins of the head and T1. Results: The results show that maximum neck flexion relative to the torso was not significantly different between the voluntary and involuntary head motions, but that the head motion was significantly greater during the involuntary sled maneuvers. Maximum flexion velocities of 450 and 1236°· s^-1 were sustained during the voluntary and involuntary maneuvers, respectively. Conclusion: These findings are important in understanding the kinematics of the human head/neck complex undergoing rapid and slow movements, and will be valuable in future studies determining a realistic physiological performance corridor for the human neck.