Plantar shear stress distribution in athletic individuals with frictional foot blisters

Background: Foot blisters are common and painful nuisances in competitive sports and in military service. The pathogenesis of the problem is related to excessive frictional forces experienced on or under the foot. The incidence of foot blisters in marathon runners can reach 39%. Similarly, up to 42% of cadets in Reserve Officers' Training Corps camps might be prone to foot blisters. Although the problem usually disappears within 5 days, a single blister might be a major problem in competitive sports or in a wilderness setting. Military training and combat effectiveness might also be compromised by foot blisters. This study sought to reveal the distribution of plantar shear forces in athletic individuals and its relevance to foot blisters. Methods: Three groups of 11 participants each were studied: blister, adult control, and pediatric control. A custom-built shear and pressure platform was used to collect plantar pressure and shear data while the participants walked over the device. Data were analyzed with repeated-measures analysis of variance. Results: The blister group had significantly increased pressure and shear stress magnitudes compared with the other groups, although no significant group-site interaction was found. The shear-time integral values were increased approximately 50% at specific sites of the athletic feet, suggesting that contact time may play a role in blister formation. Conclusions: The biomechanical interaction on the plantar surface of a blister-prone person is different from that of individuals who are less prone to the problem.