Contact Area Effects on Discomfort

Abstract

Most “ergonomic” products attempt to adopt a uniform force distribution strategy to improve comfort. The rationale being that force distribution over a large area reduces pressure and thereby enhances user comfort. However, sensory literature alludes to the concept of spatial summation, i.e. greater sensation by stimulating a larger surface area. Hence spatial summation would tend to suggest a greater discomfort when forces are applied over large surface areas. This study reports the effect of surface area on maximum discomfort causing pressure or maximum pressure tolerance (MPT). Two circular probes of different cross sectional area were used to stimulate the skin surface. The mean MPT with a probe of 5mm diameter was 3.3 times higher than the MPT with a probe of 13mm diameter. These findings suggest the following: • Perceived discomfort and contact area seem to have a “U-relationship” above a critical force value. Traditional thinking of distributing forces is successful only in the first half of the U-curve or with forces below the critical value. The section with the monotonically increasing relationship between discomfort and contact area (i.e., second half of U) may not be seen at very low forces or forces below the critical value. • “High” pressures in concentrated areas may cause less discomfort than “moderate” pressures over a larger area. • The critical or threshold pressure to induce discomfort is force and contact area dependent.