Neck muscle resistance to head impact.

The role of neck muscles in the body's response to the "whiplash" type of motion which occurs during frontal impact has been studied. This type of motion was simulated by a sudden backward pull of a subject's head. Head and neck response to low-level acceleration has been researched by recording the externally applied force, the head accelerations in the median sagittal plane, and the electrical activity in the sternomastoid muscle (EMG) as functions of time. The resultant acceleration-time curve and recorded EMG have been analyzed, with numerical values of applied resistance to the external force recorded. An analog computer model was built incorporating resistance developed by two main variable: 1) the elasticity coefficient; 2) the active damping factor. Together these two variables, combined with a resistance function, enable us to measure the resistance of the head/neck response. Using this model, variations in magnitude of these two components were studied under six varying conditions of impact: 1) length of warning time; 2) type of instruction given to the subject; 3) amount of previous experience on the part of the subject in similar situations; 4) anticipation of impact by the subject; 5) magnitude and kind of impact; 6) presence or absence of a preload.