Response of the skeletal system to helicopter-unique vibration.

An 18-month prospective skeletal system study was conducted on flying and nonflying personnel relative to chronic low-frequency vibration as experienced in helicopter flight. The aviators were initial entry students in rotary-wing training while the non-flying participants were beginning basic military training. Comparisons were made on the basis of anthropometric measurements, radiological studies, and bone mineral density changes as measured by photon absorption. The bone mineral densitometry showed no significant variation in the aviator group. A short-term 10% demineralization of the distal ulna in the non-flying group was noted immediately following the physical training. The final bone mineral density of basic training subjects returned to the initial level 18 months after the physical training. It was concluded that the helicopter aircrew members under study were exposed to levels of vibration below the threshold of vibration required to produce a measurable change in the skeletal system.