Human Neck Response during Vertical Impact with Variable Weighted Helmets

Helmet-mounted systems, such as night vision goggles and helmet-mounted displays, are designed to enhance pilot performance; however, they may also affect pilot safety during ejection due to the change in helmet inertial properties. The weight of a helmet, along with a pilot's bracing ability, can affect the human response and potential for neck injury during impact. A useful tool for investigating the mechanics of bracing and the relationships to helmet weight and impact acceleration is electromyography (EMG). Twenty-four male and female volunteer subjects participated in this study on the Vertical Deceleration Tower (VDT), located at WPAFB. The VDT produced a vertical acceleration with a half sine wave pulse of 150ms duration; peak accelerations ranged from 6 to 10 G. Helmet weights were 3.0, 4.0 and 5.0 lbs. Surface EMG was collected on the left and right sternocleidomastoid (SCM) and trapezius using DelSys surface EMG sensors. Neck loads were calculated using measured head accelerations and inertial property data. Neck load significantly increased with an increase in helmet weight. Neck muscle activity was reported in %MVC (maximum voluntary contraction). A method of collecting neck muscle activity data from the trapezius and SCM during short-duration impact experiments was successfully developed. A better understanding of the relationship between bracing and injury potential can be used to develop detailed instructions for pilots during their training to reduce their injury potential through proper positioning and bracing in the event of an ejection. Prepared in collaboration with ORISE, Oak Ridge, TN. The original document contains color images.