Sensitivity for pressure difference on the ischial tuberosity

Although research on sitting and sitting postures has been done for decades, the field of the subjective feeling of comfort or discomfort during sitting is still an unexplored field. On the basis of those studies some manufacturers claim enhanced subjective comfort because of pressure-relieving qualities of the seat cushions. The question is: does a relatively small pressure reduction enhance comfort? Before that question can be answered, the sensitivity for pressure differences applied to the skin must first be determined. The aim of this study was therefore, to determine the sensitivity of the ischial tuberosity for pressure difference in a healthy population. For this study five males and five females aged between 19 and 30 years with no exercise-induced muscle ache were selected. The (Deltaa) was determined for which stimulus (a + Deltaa) was judged as exceeding stimulus (a) in 50% of the trials. This value was called (Deltaa0.5) and was determined with an adapted simple up - down method with forced choice. Two different values for (a) were used: (a) = 13.3 kPa and (a) = 26.5 kPa and the pressure was applied with two different contact surface with diameters of 10 mm and 20 mm. For (a) = 26.5 kPa and d = 10 mm a Deltaa0.5 = 2.7 kPa was found. For (a) = 26.5 kPa and d = 20 mm a Deltaa0.5 = 3.5 kPa was found. For (a) = 13.3 kPa and d = 20 mm a Deltaa0.5 = 1.9 kPa was found.