title: Transmissibility of helicopter vibration in the spines of pilots in flight.
abstract: BACKGROUND
  The high incidence of back pain in helicopter pilots (HP) has been attributed to vibration and the in-flight pilot's posture. Helicopter vibration has a peak power at frequencies around 5 Hz, which is within the range that the human upper body presents resonance frequency. This study investigates the transmissibility (TR) of helicopter vibration from the seat to the spine of HP, and the seat resultant vibration (RSV).
  
  
  METHODS
  We monitored 12 male HP during flights lasting 2 h on average. Uniaxial accelerometers measured the vibration at the L3 and T1 spinae processes of the pilots, and the helicopter backrest. The vibration at the pilot's seat, measured by triaxial accelerometers, was taken as the reference for the estimation of transmissibility values (TR) to L3, T1, and backrest using the cross-spectral method. TR was considered only for the frequency presenting the maximum power along the seat Z acceleration, and RSV was calculated according to ISO 2631-1.
  
  
  RESULTS
  The TR values found for T1 suggest the presence of resonance in the pilot's spine during flight. Most of the HP presented TR within the range reported in the literature, but two of them had higher values at T1. Five flights showed RSV within the "caution zone" for 4-8 h of daily exposure.
  
  
  CONCLUSIONS
  Our findings indicate that cyclic compressive force due to helicopter vibration can potentially increase the load imposed on the spines of pilots during flight. This might explain the incidence of back pain and other injuries to the spines of these professionals.
authors.affiliation: Physical Activity Science Institute of Aeronautics, Rio de Janeiro, Brazil.
authors.forename: Carlos Gomes
authors.initials: CG
authors.lastname: De Oliveira
authors.forename: Jurandir
authors.initials: J
authors.lastname: Nadal
mesh_terms: D000054:Acceleration / Q000009:adverse effects; D000328:Adult; D000337:Aerospace Medicine; D000401:Aircraft; D001416:Back Pain / Q000209:etiology*; D001696:Biomechanical Phenomena; D055592:Biophysical Phenomena; D001703:Biophysics; D006801:Humans; D008297:Male; D013124:Spinal Injuries / Q000209:etiology* / Q000503:physiopathology; D014732:Vibration / Q000009:adverse effects*; D016474:Weight-Bearing / Q000502:physiology