Basic physical characteristics of the neck have been defined which have application to the design of biomechanical models, anthropometric dummies, and occupant crash protection devices. The study was performed using a group of 180 volunteers chosen on the basis of sex, age (18-74 years), and stature. Measurements from each subject included anthropometry, cervical range-of-motion (observed with both x-rays and photographs), the dynamic response of the cervical flexor and extensor muscles to a controlled jerk, and the maximum voluntary strength of the cervical muscles. Data are presented in tabular and graphic form for total range-of-motion, cervical muscle reflex time, decelerations of the head, muscle activation time, and cervical muscle strength.
The range-of-motion of females was found to average 1-12 deg greater than that of males, depending upon age, and a definite degradation in range-of-motion was observed with increasing age. Average neck muscle reflex times range from 56-92 ms for flexors and 54-87 ms for extensors, with males being generally slower-reacting. This finding means that the cervical muscles generally cannot be activated in sufficient time to mitigate the hyperextension effects of a surprise rearend collision. Reflex time becomes significantly longer after middle age. On the average, the stretch reflex was elicited with head accelerations at the c.g. of approximately 0.25 g. The time required to stop the head after initial detection of the muscle reflex was slightly longer for neck extensors. Strength tests revealed that males are on the average stronger than females in both flexor and extensor strengths; that males and females exhibit different aging characteristics, and that a slight stature effect was present in the younger and shorter portions of the population.
Age and sex were found to be important factors in cervical flexibility and response characteristics, and they should be included whenever accurate representation of neck parameters is desired.