Spectral analysis of cerebral oxygenation responses to seated whole-body vibration in healthy men

The objective of this study was to assess the effects of WBV on cerebral oxygenation oscillations of the pre-frontal cortex region in healthy men based on the wavelet transform of near-infrared spectroscopy (NIRS) signals. On three separate days, twelve participants were exposed to WBV (3, 4.5 and 6 Hz) in a randomized order. Cerebral oxygenation signal was monitored from the left frontal lobe using NIRS before, during and recovery from WBV. With spectral analysis based on wavelet transform, five frequency intervals were identified (I, 0.005-0.02 Hz; II, 0.02-0.06 Hz; III, 0.06-0.15 Hz; IV, 0.15-0.40 Hz; and V, 0.40-2.0 Hz). It was found that at WBV 4.5 and 6 Hz, the amplitudes of the Δ[Hb], Δ[HbO2] and Δ[tHb] oscillations during WBV in the frequency intervals I, II, III and V were higher as compared to that of at 3 Hz. However, no significant differences in the amplitude of cerebral oxygenation oscillations were found between WBV frequencies 4.5 and 6 Hz. This study demonstrates that WBV at 4.5 Hz induce highest cerebral oscillation responses. The enhancement of the cerebral spontaneous oscillation activity indicates an activation of the pre-frontal cortex region and an increased demand for oxygen. At prolonged regional neuronal activity due to vibration exposure, energy demand might exceed energy supply, and an imbalance might occur in brain regions activated. This might contribute to the development of fatigue in occupations exposed to WBV. Relevance to industry: Occupations exposed to WBV while driving are at increased risk of accidents. This study examined cerebral oxygenation oscillations in response to WBV at 3, 4.5 and 6 Hz to assess if the activation of the pre-frontal cortex region was a potential contributor to the development of central fatigue.