PASSIVE STIFFNESS OF THE HUMAN NECK IN FLEXION, EXTENSION, AND LATERAL BENDING

The passive bending stiffness, tolerable bending moment levels, and el astic energy storage capabilities of the cervical spine were evaluated in 40 male and 19 female volunteer subjects from a university student population, about the flexion, extension, and lateral bending axes. B ending moments were applied to the neck while subjects lay on a fricti onless jig and simultaneous angular displacements of the skull relativ e to the rib cage were recorded. Myoelectric signals from the sternocl eidomastoid and splenius capitis muscles were amplified over audio spe akers to train subjects to relax their musculature. Tolerable levels o f bending moments were quite low (less than 10 N m on average for all conditions) given the very large magnitude of bending moment applied t o the neck estimated from impact models. Subjects tolerated greater mo ment and elastic energy storage in the cervical passive tissues during flexion than in both extension and in lateral bending. In addition ma les were able to tolerate larger applied moments, were stiffer, and st ored more energy than females in all loading conditions. The data deri ved from this study of loading at very slow rates provide a lower limi t for bending moments and for cervical spine stiffness, and yield a fi rst approximation to dynamic bending stiffness values that may be incl uded in models of the cervical spine.