Occupants of automobiles experience discomfort after long drives, irrespective of how well designed a seat might be. Previous studies of discomfort during driving have focused either on the seat shape and materials (“static” properties), long-term discomfort (“fatigue” properties), or dynamics (“vibration” properties). These factors have previously not been considered together. This paper reports three studies with objectives to define and test a model for describing long-term discomfort from vibration. Study 1 was an independent measures laboratory trial using an automobile seat, which lasted 80 minutes; Study 2 was a repeated measures laboratory trial using a rail passenger seat, which lasted 60 minutes; Study 3 was a repeated measures field trial in a people carrier automobile, which involved 70 minutes of travelling. The findings showed that discomfort accrues with time but that more discomfort is experienced when subjects are also exposed to whole-body vibration. Exposure to whole-body vibration accelerates development of discomfort. The relationship between the reported discomfort, the vibration magnitude, and the exposure time can be described using a multifactorial linear model. It is concluded that ignoring parts of the multi-factorial model (i.e., static, dynamic, or temporal factors) will compromise understanding of discomfort in context. 1. Introduction Long-term exposure to vibration whilst driving or travelling as a passenger in an automobile has been associated with discomfort, increased prevalence of low back pain, and other musculoskeletal disorders (e.g. [1–7]). Subjective reports of discomfort are often considered as precursors of injury, and much experimental work on physical effects of whole-body vibration has used subjective ratings of discomfort as the experimental method. Factors affecting the discomfort could include the physical shape of the seat, the fit of the seat to the occupant, the materials which the seat is made from (which will dictate its stiffness), the thermal environment to which the occupant is exposed, exposure to whole-body vibration and/or mechanical shocks, opportunity for changing postures (thus changing the muscle groups which are supporting the body weight), and the length of time the occupant has been sitting in the seat (e.g. [8, 9]). Ebe and Griffin [3, 4] proposed a qualitative and quantitative model of overall seat discomfort. The approach of their model was to separate discomfort into “static” seat factors and “dynamic” seat factors. Static factors focused on seat stiffness, but these could also
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