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In an effort to create computer models to promote rapid, cost-effective prototyping while easing design changes, more information about how people interact with seats is needed. Predicting the occupant location, their geometry, and motion within a vehicle leads to a better determination of safety restraint location, controls reach, and visibility - factors that affect the overall operation of the vehicle. Based on the Michigan State University JOHN model, which provides a biomechanical simulation of the torso posture, experiments were conducted to examine the change of postures due to seat and interior package factors. The results can be incorporated into the posture prediction model of the RAMSIS program to give a more detailed prognosis of the spine curvature and refine the model-seat interactions. This paper will address findings of the experimental study with relation to model development.

The design and evaluation of seating has been limited by the available technologies to measure the mechanical interaction between a seat and its user. For many years, representation of the seated torso has been by two standardized measurement manikins from the American National Standards Institute (ANSI)1 for office seating and the Society of Automotive Engineers (SAE)2 for vehicle seating. Most office and automotive seat backs recline about a single point; this motion can be measured with the available manikins. However, both the ANSI and the SAE manikins do not represent the natural anatomical movements of the upper torso (thorax) relative to the lower torso (pelvis) that occur with spinal articulation. Current tools that are useful for seat design and evaluation include the biomechanical models3,4 and experimental test methods5, 6,7 that have been developed at Michigan State University's (MSU) Biomechanical Design Research Laboratory (BDRL).

The ASPECT (Automotive Seat and Package Evaluation and Comparison Tools) Program has developed the next generation SAE 3-D H-Point testing manikin. During the development of the ASPECT manikin, new data were collected on how people loaded different regions of a seat and how these loads varied with different postures. These data, along with a computer model of the ASPECT manikin, were used to assist in the development of a human-like weight distribution for the new seating device, the ASPECT manikin.

A need to develop methodologies to obtain objective measurements of the effects of different seat contours on people is evident. In an effort to monitor muscle activity during static seated postures, electromyography (EMG) was employed. In an experimental setting, fatigue was induced in back extensor muscles for different seated postures. The resultant EMG signals were then sampled bilaterally for three different vertebral levels and the effects of the different seating systems on posture were evaluated. In preliminary tests involving 4 subjects of similar size and build, utilizing three differently contoured seats, findings support the use of EMG to quantify muscular fatigue as a viable means of objectively measuring the effects of different seat contours.