KINEMATIC RESPONSE OF THE NECK TO VOLUNTARY AND INVOLUNTARY FLEXION

Methods: The dynamic head-neck responses of human subjects and cadaver s undergoing involuntary impact loading conditions have been studied e xtensively in order to define the kinematics of the neck undergoing ra pid movements, but little detailed information is available regarding slower, voluntary motions. In this study, the dynamic kinematics of he ad/neck complex during subject-controlled, or voluntary head motion ha ve been investigated to compare with the kinematics to involuntary res ponse. Five male human subjects experienced two-types of posterior/ an terior neck flexion: flexion initiated under their own volition, and f lexion 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 cap tured the photo target motion. Linear and angular displacement and vel ocity of the head and T1 and sled were computed using customized data- processing software. The neck kinematics were represented by a 2-pin l inkage which connected the anatomical origins of the head and T1. Resu lts: 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 durin g the involuntary sled maneuvers. Maximum flexion velocities of 450 an d 1236 degrees.s(-1) were sustained during the voluntary and involunta ry maneuvers, respectively. Conclusion: These findings are important i n understanding the kinematics of the human head/neck complex undergoi ng rapid and slow movements, and will be valuable in future studies de termining a realistic physiological performance corridor for the human neck.