Characterization of the frequency and muscle responses of the lumbar and thoracic spines of seated volunteers during sinusoidal whole body vibration

INTRODUCTION Vibration exposure has been linked to chronic neck and lower back pain The aim of this study was to characterize the frequency response of seated human volunteers during WBV exposures along the vertical axis in order to define the resonant frequency at the lumbar and thoracic spines and to compare the outcomes derived directly from accelerometers to those derived from an indirect image-based approach. Electromyography also was used to measure muscle activity at both spinal regions in order to compare the corresponding muscle and resonance responses for varied input WBV frequencies. METHODS Under USAMRMC IRB-approved procedures and with informed consent, male volunteers (n=5; 24.8±2.2 years; 73.9±7.3kg; standing height 1.8±0.1m) underwent seated WBV in the vertical direction Each subject was exposed to a vertical sine sweep vibration ranging from 2-19Hz with a 0.4g amplitude, for a total exposure of 70 seconds. Each signal was segmented into 35 2-second epochs in order to determine the frequency, transmissibility, and muscle response. Frequency was calculated using spectral analysis in MATLAB