Equivalent comfort contours for whole-body vertical vibration: effect of backrest inclination

Abstract

The inclination of a backrest may be expected to alter the vibration transmitted to the body and the associated vibration discomfort. This study examined the influence of backrest inclination on the discomfort arising from whole-body vertical vibration when sitting in a rigid seat with a backrest inclined at 0? (upright), 30?, 60? and 90? (recumbent). Equivalent comfort contours were determined over the frequency range from 1 to 20 Hz and over the magnitude range from 0.2 to 2.0 ms 2 r.m.s. relative to the discomfort caused by 8-Hz vertical vibration at 0.4 ms-2 r.m.s. When sitting with the backrest inclined to 60? or 90?, there was less discomfort around 5 and 6.3 Hz than when sitting with the upright backrest. Around 16 and 20 Hz there was greater discomfort when sitting with the backrest inclined to 30?, 60?, and 90? than when sitting with the upright backrest. The reductions in discomfort at the lower frequencies may be associated with increased postural support and changes in the biodynamic responses of the body when reclined. Increased transmission of vibration to the head may explain the greater discomfort at high frequencies when sitting reclined. It is concluded that different methods of vibration evaluation are appropriate when evaluating vibration with upright and inclined backrests.

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ORCID for M.J. Griffin: orcid.org/0000-0003-0743-9502

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