Spine Load in the Context of Automotive Seating 2007-01-2485

In modern society the automobile is an essential companion in everyday life. Be it commuting to and from work or during our leisure time - every week most of us spend many hours sitting in their car. In this context the seat is the main interface between the human being and the automobile itself. Functioning well, this close relationship can foster the well-being of the passenger and raise his spirit; being flawed it can otherwise cause severe pain in the back after a longer journey. Thus, for car manufacturers, the aspects of seat comfort are becoming more and more prominent in distinguishing themselves from their competitors. Despite its importance the development of comfort parameters in automotive seating is still being consigned to the subjective judgements of a poor number of seating experts or randomly selected test subjects. Easily influenceable by parameters like affection, physical conditions or environmental factors and a lack of standardization these subjective evaluations have a big intra individual and inter individual range.

A first approach to improve the objective judgement of an automotive seat was made by the concept of “optimal” load distribution (Mergl, 2006; Zenk, 2006), based on the identification of a close interconnection between the pressure on the seat and the discomfort felt by the person sitting on it. In the next step further objectification of seat comfort will be achieved by an in vivo measuring of the pressure in the spinal disc, which is a reliable indicator for the load in the spine.

For this experiment a pressure sensor is implanted with a canula in the middle of an intervertebral disc of a voluntary subject. In this way the local pressure on the disc is measured in an automobile, concentrating on the very seat settings which cause pain in the upper back. The significant lowest pressure values (0.5 bar) are achieved in an ideal seat position with an “optimal” load distribution. By contrast the pressure on the disc increases by load distributions differing from an optimal one.

From these results we will be able to improve our knowledge on how to avoid uncomfortable seating in automobiles and start making well-founded recommendations for seat design.