An experimental investigation on the relationship between seat pan and seat back angles to eliminate the shear force on the seat pan.

This work aimed to establish the relationship between seat back and seat pan angles to eliminate the seat pan shear force for a large range of seat configurations. Thirty-nine volunteers participated in the experiment. A reconfigurable experimental seat was used. Seven seat back angles ranging from 0 (vertical) to 60° were tested. For each, starting from a preferred seat pan angle self-selected by participants, an experimenter manually adjusted it so that the shear on the seat pan surface fell within [-5N, 5N] while the pelvis was controlled to keep in contact with the seat back. Results suggested a parabolic relationship between seat back and seat pan angles with a peak of about 14.9° at 40 degrees of seat back angle. On average, the zero-shear seat pan angle was 4.2° higher than the preferred one and the use of a leg support increased zero-shear angle by 4.4°.