The Effect of Rotational Vibration In Roll and Pitch Axes on the Discomfort of Seated Subjects

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Abstract
The effects were studied of vibration level, frequency and foot position on the discomfort of seated persons subjected to sinusoidal vibration in roll and pitch axes. Using the method of category production, 8 seated subjects adjusted roll and pitch vibrations to levels described as uncomfortable on a given semantic scale. The axes of rotation were located on the same horizontal plane as the ischial tuberosities of the subjects. In each axis subjects assessed the discomfort of 6 frequencies (1.6, 2.0, 4.0, 8.0, 16.0 31.5 Hz) for each of 4 different heights of a stationary foot-rest and a condition where no foot-rest was used. For all conditions where a foot-rest was present rotational vibration in roll produced greater discomfort than the same level of rotational vibration in pitch. Sensitivity to rotational acceleration decreased with increasing frequency in both roll and pitch axes for all foot positions. Subjects became less sensitive to rotational vibration in roll and especially pitch as foot height was raised. This was attributed to the decreased contact between the rotating seat and the thighs at higher foot positions.