Abstract
Independent groups of male college student volunteers were exposed in a standard seated posture to one of 5 conditions of vertical (Z-axis) harmonic oscillation for two hours or until vomiting. A control condition, sinusoidal motion at 0.17 Hz with a root mean square acceleration of 0.13 g, served as the basis of comparison with the remaining four conditions, which were generated by the sum of two sinusoids, namely, the fundamental at 0.17 Hz plus the second (0.33 Hz) or third (0.50 Hz) harmonic. The experimental conditions differed either in the phase relationship or the relative acceleration level of the added harmonic. The predicted motion sickness incidence (MSI) was calculated for each sinusoid alone from a previously derived mathematical model and compared with the obtained MSIs. While the overall differences may have been due to chance, certain motion combinations provoked unexpectedly high MSI. No simple relationship between predicted MSI for single-frequency motion and the obtained complex-motion MSIs emerged from this study. Until further data are forthcoming, guidelines for motion sickness prevention based on the presumption of independence of action of component frequencies in a complex motion must be interpreted with caution.
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