Vibration discomfort of supine human body exposed to whole-body vibration: effect of vibration direction and magnitude.

Supine postures are increasingly adopted in medical transport, long-duration flights, and other healthcare environments. This study is aimed to identify the effect of vibration direction and magnitude on the objective and subjective responses of the human body in a supine posture. The transmissibilities to the head, chest, abdomen, and thighs of 12 male subjects were measured with single-axis random vibrations in longitudinal (z axis), lateral (y axis), and vertical (x axis) direction at 0.2, 0.4, 0.6, and 0.8 ms-2 r.m.s. Subjective discomfort was determined using the absolute magnitude estimation method. It was found factors of 1.0, 1.5 and 1.0 multiplying with the weighted r.m.s. of input accelerations in x, y, and z axes, respectively, can predict the discomfort. Alternatively, the unweighted acceleration measured at the body, such as at the chest, which was found to highly correlate with vibration discomfort, can be used to predict vibration discomfort of supine subjects.