Helmeted head and neck dynamics under whole-body vibration

he military aviator's helmet functions as both protective gear and as an equipment mounting platform for devices that enhance aviator performance. These devices include night vision goggles, head-up displays, sighting systems, and other gear such as multiple visors and chemical protective masks. This additional equipment alters the helmet mass and center of mass, which in turn, increases the load on the muscles of the neck. This study investigated sagittally symmetric changes in head supported mass (M) and center of mass (CM) for effects on head and neck posture, acceleration, and neck myoelectric responses under whole-body vibration.;Twelve volunteer male aviators were exposed to short duration axially swept sinusoidal vibration while wearing twelve different helmet configurations. These configurations consisted of three masses of 2, 3, and 4 Kg, and four center of masses of ;Results showed that postural static moments remained constant with no significant changes in head, neck, or trunk angle as a function of vibration frequency, M, or CM parameters. Acceleration measurements showed significant increases in head pitch acceleration at resonance, but no changes in resonant frequency, for changes in M and CM. Consistent resonant frequencies suggest the head and neck system is not a passive system but is actively controlled by the muscles of the neck. Myoelectric responses in the neck showed significant increases in peak RMS activity for posterior muscles and were highly correlated with head pitch acceleration (r...