Effect of body supination angle on subjective response to whole-body vibration.

Three experiments were conducted to evaluate the subjective symptomatology associated with various combinations of supination angle and vibration spectral composition. Sinusoidal, sum-of-sine, and random vibration were used in the first, second and third experiments, respectively. All exposure periods were 40 s and the supination angle was varied from 13-65 degrees. Subjective response was evaluated by means of a physical symptom survey incorporating a discomfort rating scale. For all three experiments, the results indicated a primary effect of supination angle was to shift the vibration-induced sensations across body regions. Small angles (nearly seated upright) were most often associated with stomach, abdomen, and head discomfort; large angles were most often associated with upper back, neck, and sacral discomfort. With respect to the calculated total-body response, results indicated a preference for the 30 degree supination angle for both complex vibration spectrums used and for all three sinusoidal frequencies. This findings suggests the existence of an optimal supination angle for comfort under vibration.