Contoured cushioning: effects of surface compressibility and curvature on heel pressure distribution

• Published in: Footwear science Vol. 3; no. 1; pp. 23 - 32
• Main Authors: Mientjes, Martine I.V., Shorten, Martyn
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Group 01.01.2011; Taylor & Francis Ltd
• Subjects: compressibility; contact theory; curvature; footwear; heel cushioning; Hertz; Pressure distribution; Studies
• ISSN: 1942-4280; 1942-4299
• DOI: 10.1080/19424280.2010.536587

This study investigated the combined effects of cushioning system material properties and geometry on pressure distribution under the heel in eight healthy male subjects. Pressure distribution and normal force under the heel were measured while subjects stood on moulded foam surfaces presenting sixteen, systematically varying combinations of material compressibility and surface curvature. Subjects used visual force feedback to maintain a constant, approximately even heel-forefoot weight distribution during the 1-s data collections. A two-way analysis of variance with repeated measures, using surface modulus and surface radius as factors, was used to test the significance of differences among condition means. Compressibility and curvature were found to have similar effects on pressure distribution. More compressible and more conforming surfaces both reduced peak pressure under the calcaneus and redistributed load to peripheral regions. Effect magnitudes became smaller as peak pressure approached the minimum possible value. Curvature had greater influence on peak pressure when presented in combination with less compressible surface materials and vice versa. Qualitative pressure distribution outcomes were well described by Hertz contact theory and a least-squares contact model accounted for 94% of the observed variance in peak pressure. The quantitative correspondence between theory and experimental results is not expected to hold under higher loads and more dynamic loading conditions. The results of this study validate the practice of using contoured footbeds and conforming shoe sole surfaces as a means of reducing peak pressure, especially when space or other functional requirements limit the use of compressible cushioning materials.